Commit | Line | Data |
---|---|---|
1da177e4 LT |
1 | <?xml version="1.0" encoding="UTF-8"?> |
2 | <!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN" | |
3 | "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []> | |
4 | ||
5 | <book id="libataDevGuide"> | |
6 | <bookinfo> | |
7 | <title>libATA Developer's Guide</title> | |
8 | ||
9 | <authorgroup> | |
10 | <author> | |
11 | <firstname>Jeff</firstname> | |
12 | <surname>Garzik</surname> | |
13 | </author> | |
14 | </authorgroup> | |
15 | ||
16 | <copyright> | |
4f931374 | 17 | <year>2003-2006</year> |
1da177e4 LT |
18 | <holder>Jeff Garzik</holder> |
19 | </copyright> | |
20 | ||
21 | <legalnotice> | |
22 | <para> | |
23 | The contents of this file are subject to the Open | |
24 | Software License version 1.1 that can be found at | |
25 | <ulink url="http://www.opensource.org/licenses/osl-1.1.txt">http://www.opensource.org/licenses/osl-1.1.txt</ulink> and is included herein | |
26 | by reference. | |
27 | </para> | |
28 | ||
29 | <para> | |
30 | Alternatively, the contents of this file may be used under the terms | |
31 | of the GNU General Public License version 2 (the "GPL") as distributed | |
32 | in the kernel source COPYING file, in which case the provisions of | |
33 | the GPL are applicable instead of the above. If you wish to allow | |
34 | the use of your version of this file only under the terms of the | |
35 | GPL and not to allow others to use your version of this file under | |
36 | the OSL, indicate your decision by deleting the provisions above and | |
37 | replace them with the notice and other provisions required by the GPL. | |
38 | If you do not delete the provisions above, a recipient may use your | |
39 | version of this file under either the OSL or the GPL. | |
40 | </para> | |
41 | ||
42 | </legalnotice> | |
43 | </bookinfo> | |
44 | ||
45 | <toc></toc> | |
46 | ||
07dd39b9 JG |
47 | <chapter id="libataIntroduction"> |
48 | <title>Introduction</title> | |
49 | <para> | |
50 | libATA is a library used inside the Linux kernel to support ATA host | |
51 | controllers and devices. libATA provides an ATA driver API, class | |
52 | transports for ATA and ATAPI devices, and SCSI<->ATA translation | |
53 | for ATA devices according to the T10 SAT specification. | |
54 | </para> | |
55 | <para> | |
56 | This Guide documents the libATA driver API, library functions, library | |
57 | internals, and a couple sample ATA low-level drivers. | |
58 | </para> | |
59 | </chapter> | |
60 | ||
1da177e4 LT |
61 | <chapter id="libataDriverApi"> |
62 | <title>libata Driver API</title> | |
92bab26b JG |
63 | <para> |
64 | struct ata_port_operations is defined for every low-level libata | |
65 | hardware driver, and it controls how the low-level driver | |
66 | interfaces with the ATA and SCSI layers. | |
67 | </para> | |
68 | <para> | |
69 | FIS-based drivers will hook into the system with ->qc_prep() and | |
70 | ->qc_issue() high-level hooks. Hardware which behaves in a manner | |
71 | similar to PCI IDE hardware may utilize several generic helpers, | |
72 | defining at a bare minimum the bus I/O addresses of the ATA shadow | |
73 | register blocks. | |
74 | </para> | |
1da177e4 LT |
75 | <sect1> |
76 | <title>struct ata_port_operations</title> | |
77 | ||
92bab26b | 78 | <sect2><title>Disable ATA port</title> |
1da177e4 LT |
79 | <programlisting> |
80 | void (*port_disable) (struct ata_port *); | |
81 | </programlisting> | |
82 | ||
83 | <para> | |
84 | Called from ata_bus_probe() and ata_bus_reset() error paths, | |
85 | as well as when unregistering from the SCSI module (rmmod, hot | |
86 | unplug). | |
8b2af8f0 EF |
87 | This function should do whatever needs to be done to take the |
88 | port out of use. In most cases, ata_port_disable() can be used | |
89 | as this hook. | |
90 | </para> | |
91 | <para> | |
92 | Called from ata_bus_probe() on a failed probe. | |
93 | Called from ata_bus_reset() on a failed bus reset. | |
94 | Called from ata_scsi_release(). | |
1da177e4 LT |
95 | </para> |
96 | ||
92bab26b JG |
97 | </sect2> |
98 | ||
99 | <sect2><title>Post-IDENTIFY device configuration</title> | |
1da177e4 LT |
100 | <programlisting> |
101 | void (*dev_config) (struct ata_port *, struct ata_device *); | |
102 | </programlisting> | |
103 | ||
104 | <para> | |
105 | Called after IDENTIFY [PACKET] DEVICE is issued to each device | |
106 | found. Typically used to apply device-specific fixups prior to | |
107 | issue of SET FEATURES - XFER MODE, and prior to operation. | |
108 | </para> | |
8b2af8f0 EF |
109 | <para> |
110 | Called by ata_device_add() after ata_dev_identify() determines | |
111 | a device is present. | |
112 | </para> | |
113 | <para> | |
114 | This entry may be specified as NULL in ata_port_operations. | |
115 | </para> | |
1da177e4 | 116 | |
92bab26b JG |
117 | </sect2> |
118 | ||
119 | <sect2><title>Set PIO/DMA mode</title> | |
1da177e4 LT |
120 | <programlisting> |
121 | void (*set_piomode) (struct ata_port *, struct ata_device *); | |
122 | void (*set_dmamode) (struct ata_port *, struct ata_device *); | |
5444a6f4 AC |
123 | void (*post_set_mode) (struct ata_port *); |
124 | unsigned int (*mode_filter) (struct ata_port *, struct ata_device *, unsigned int); | |
1da177e4 LT |
125 | </programlisting> |
126 | ||
127 | <para> | |
128 | Hooks called prior to the issue of SET FEATURES - XFER MODE | |
5444a6f4 AC |
129 | command. The optional ->mode_filter() hook is called when libata |
130 | has built a mask of the possible modes. This is passed to the | |
131 | ->mode_filter() function which should return a mask of valid modes | |
132 | after filtering those unsuitable due to hardware limits. It is not | |
133 | valid to use this interface to add modes. | |
134 | </para> | |
135 | <para> | |
136 | dev->pio_mode and dev->dma_mode are guaranteed to be valid when | |
137 | ->set_piomode() and when ->set_dmamode() is called. The timings for | |
138 | any other drive sharing the cable will also be valid at this point. | |
139 | That is the library records the decisions for the modes of each | |
140 | drive on a channel before it attempts to set any of them. | |
141 | </para> | |
142 | <para> | |
143 | ->post_set_mode() is | |
1da177e4 LT |
144 | called unconditionally, after the SET FEATURES - XFER MODE |
145 | command completes successfully. | |
146 | </para> | |
147 | ||
148 | <para> | |
149 | ->set_piomode() is always called (if present), but | |
150 | ->set_dma_mode() is only called if DMA is possible. | |
151 | </para> | |
152 | ||
92bab26b JG |
153 | </sect2> |
154 | ||
155 | <sect2><title>Taskfile read/write</title> | |
1da177e4 LT |
156 | <programlisting> |
157 | void (*tf_load) (struct ata_port *ap, struct ata_taskfile *tf); | |
158 | void (*tf_read) (struct ata_port *ap, struct ata_taskfile *tf); | |
159 | </programlisting> | |
160 | ||
161 | <para> | |
162 | ->tf_load() is called to load the given taskfile into hardware | |
163 | registers / DMA buffers. ->tf_read() is called to read the | |
164 | hardware registers / DMA buffers, to obtain the current set of | |
165 | taskfile register values. | |
8b2af8f0 EF |
166 | Most drivers for taskfile-based hardware (PIO or MMIO) use |
167 | ata_tf_load() and ata_tf_read() for these hooks. | |
1da177e4 LT |
168 | </para> |
169 | ||
92bab26b JG |
170 | </sect2> |
171 | ||
bf717b11 JG |
172 | <sect2><title>PIO data read/write</title> |
173 | <programlisting> | |
174 | void (*data_xfer) (struct ata_device *, unsigned char *, unsigned int, int); | |
175 | </programlisting> | |
176 | ||
177 | <para> | |
178 | All bmdma-style drivers must implement this hook. This is the low-level | |
179 | operation that actually copies the data bytes during a PIO data | |
180 | transfer. | |
181 | Typically the driver | |
182 | will choose one of ata_pio_data_xfer_noirq(), ata_pio_data_xfer(), or | |
183 | ata_mmio_data_xfer(). | |
184 | </para> | |
185 | ||
186 | </sect2> | |
187 | ||
92bab26b | 188 | <sect2><title>ATA command execute</title> |
1da177e4 LT |
189 | <programlisting> |
190 | void (*exec_command)(struct ata_port *ap, struct ata_taskfile *tf); | |
191 | </programlisting> | |
192 | ||
193 | <para> | |
194 | causes an ATA command, previously loaded with | |
195 | ->tf_load(), to be initiated in hardware. | |
8b2af8f0 EF |
196 | Most drivers for taskfile-based hardware use ata_exec_command() |
197 | for this hook. | |
1da177e4 LT |
198 | </para> |
199 | ||
92bab26b JG |
200 | </sect2> |
201 | ||
202 | <sect2><title>Per-cmd ATAPI DMA capabilities filter</title> | |
780a87f7 JG |
203 | <programlisting> |
204 | int (*check_atapi_dma) (struct ata_queued_cmd *qc); | |
205 | </programlisting> | |
206 | ||
207 | <para> | |
208 | Allow low-level driver to filter ATA PACKET commands, returning a status | |
209 | indicating whether or not it is OK to use DMA for the supplied PACKET | |
210 | command. | |
211 | </para> | |
8b2af8f0 EF |
212 | <para> |
213 | This hook may be specified as NULL, in which case libata will | |
214 | assume that atapi dma can be supported. | |
215 | </para> | |
780a87f7 | 216 | |
92bab26b JG |
217 | </sect2> |
218 | ||
219 | <sect2><title>Read specific ATA shadow registers</title> | |
1da177e4 LT |
220 | <programlisting> |
221 | u8 (*check_status)(struct ata_port *ap); | |
780a87f7 | 222 | u8 (*check_altstatus)(struct ata_port *ap); |
1da177e4 LT |
223 | </programlisting> |
224 | ||
225 | <para> | |
bf717b11 | 226 | Reads the Status/AltStatus ATA shadow register from |
780a87f7 JG |
227 | hardware. On some hardware, reading the Status register has |
228 | the side effect of clearing the interrupt condition. | |
8b2af8f0 EF |
229 | Most drivers for taskfile-based hardware use |
230 | ata_check_status() for this hook. | |
231 | </para> | |
232 | <para> | |
233 | Note that because this is called from ata_device_add(), at | |
234 | least a dummy function that clears device interrupts must be | |
235 | provided for all drivers, even if the controller doesn't | |
236 | actually have a taskfile status register. | |
1da177e4 LT |
237 | </para> |
238 | ||
92bab26b JG |
239 | </sect2> |
240 | ||
241 | <sect2><title>Select ATA device on bus</title> | |
1da177e4 LT |
242 | <programlisting> |
243 | void (*dev_select)(struct ata_port *ap, unsigned int device); | |
244 | </programlisting> | |
245 | ||
246 | <para> | |
247 | Issues the low-level hardware command(s) that causes one of N | |
248 | hardware devices to be considered 'selected' (active and | |
780a87f7 | 249 | available for use) on the ATA bus. This generally has no |
8b2af8f0 EF |
250 | meaning on FIS-based devices. |
251 | </para> | |
252 | <para> | |
253 | Most drivers for taskfile-based hardware use | |
254 | ata_std_dev_select() for this hook. Controllers which do not | |
255 | support second drives on a port (such as SATA contollers) will | |
256 | use ata_noop_dev_select(). | |
1da177e4 LT |
257 | </para> |
258 | ||
92bab26b JG |
259 | </sect2> |
260 | ||
5444a6f4 AC |
261 | <sect2><title>Private tuning method</title> |
262 | <programlisting> | |
263 | void (*set_mode) (struct ata_port *ap); | |
264 | </programlisting> | |
265 | ||
266 | <para> | |
267 | By default libata performs drive and controller tuning in | |
268 | accordance with the ATA timing rules and also applies blacklists | |
269 | and cable limits. Some controllers need special handling and have | |
270 | custom tuning rules, typically raid controllers that use ATA | |
271 | commands but do not actually do drive timing. | |
272 | </para> | |
273 | ||
274 | <warning> | |
275 | <para> | |
276 | This hook should not be used to replace the standard controller | |
277 | tuning logic when a controller has quirks. Replacing the default | |
278 | tuning logic in that case would bypass handling for drive and | |
279 | bridge quirks that may be important to data reliability. If a | |
280 | controller needs to filter the mode selection it should use the | |
281 | mode_filter hook instead. | |
282 | </para> | |
283 | </warning> | |
284 | ||
285 | </sect2> | |
286 | ||
92bab26b | 287 | <sect2><title>Control PCI IDE BMDMA engine</title> |
1da177e4 LT |
288 | <programlisting> |
289 | void (*bmdma_setup) (struct ata_queued_cmd *qc); | |
290 | void (*bmdma_start) (struct ata_queued_cmd *qc); | |
780a87f7 JG |
291 | void (*bmdma_stop) (struct ata_port *ap); |
292 | u8 (*bmdma_status) (struct ata_port *ap); | |
1da177e4 LT |
293 | </programlisting> |
294 | ||
295 | <para> | |
780a87f7 JG |
296 | When setting up an IDE BMDMA transaction, these hooks arm |
297 | (->bmdma_setup), fire (->bmdma_start), and halt (->bmdma_stop) | |
298 | the hardware's DMA engine. ->bmdma_status is used to read the standard | |
299 | PCI IDE DMA Status register. | |
300 | </para> | |
301 | ||
302 | <para> | |
303 | These hooks are typically either no-ops, or simply not implemented, in | |
304 | FIS-based drivers. | |
1da177e4 | 305 | </para> |
8b2af8f0 EF |
306 | <para> |
307 | Most legacy IDE drivers use ata_bmdma_setup() for the bmdma_setup() | |
308 | hook. ata_bmdma_setup() will write the pointer to the PRD table to | |
309 | the IDE PRD Table Address register, enable DMA in the DMA Command | |
310 | register, and call exec_command() to begin the transfer. | |
311 | </para> | |
312 | <para> | |
313 | Most legacy IDE drivers use ata_bmdma_start() for the bmdma_start() | |
314 | hook. ata_bmdma_start() will write the ATA_DMA_START flag to the DMA | |
315 | Command register. | |
316 | </para> | |
317 | <para> | |
318 | Many legacy IDE drivers use ata_bmdma_stop() for the bmdma_stop() | |
319 | hook. ata_bmdma_stop() clears the ATA_DMA_START flag in the DMA | |
320 | command register. | |
321 | </para> | |
322 | <para> | |
323 | Many legacy IDE drivers use ata_bmdma_status() as the bmdma_status() hook. | |
324 | </para> | |
1da177e4 | 325 | |
92bab26b JG |
326 | </sect2> |
327 | ||
328 | <sect2><title>High-level taskfile hooks</title> | |
1da177e4 LT |
329 | <programlisting> |
330 | void (*qc_prep) (struct ata_queued_cmd *qc); | |
331 | int (*qc_issue) (struct ata_queued_cmd *qc); | |
332 | </programlisting> | |
333 | ||
334 | <para> | |
335 | Higher-level hooks, these two hooks can potentially supercede | |
336 | several of the above taskfile/DMA engine hooks. ->qc_prep is | |
337 | called after the buffers have been DMA-mapped, and is typically | |
338 | used to populate the hardware's DMA scatter-gather table. | |
339 | Most drivers use the standard ata_qc_prep() helper function, but | |
340 | more advanced drivers roll their own. | |
341 | </para> | |
342 | <para> | |
343 | ->qc_issue is used to make a command active, once the hardware | |
344 | and S/G tables have been prepared. IDE BMDMA drivers use the | |
345 | helper function ata_qc_issue_prot() for taskfile protocol-based | |
780a87f7 | 346 | dispatch. More advanced drivers implement their own ->qc_issue. |
1da177e4 | 347 | </para> |
8b2af8f0 EF |
348 | <para> |
349 | ata_qc_issue_prot() calls ->tf_load(), ->bmdma_setup(), and | |
350 | ->bmdma_start() as necessary to initiate a transfer. | |
351 | </para> | |
1da177e4 | 352 | |
92bab26b JG |
353 | </sect2> |
354 | ||
bf717b11 | 355 | <sect2><title>Exception and probe handling (EH)</title> |
1da177e4 LT |
356 | <programlisting> |
357 | void (*eng_timeout) (struct ata_port *ap); | |
bf717b11 JG |
358 | void (*phy_reset) (struct ata_port *ap); |
359 | </programlisting> | |
360 | ||
361 | <para> | |
362 | Deprecated. Use ->error_handler() instead. | |
363 | </para> | |
364 | ||
365 | <programlisting> | |
366 | void (*freeze) (struct ata_port *ap); | |
367 | void (*thaw) (struct ata_port *ap); | |
368 | </programlisting> | |
369 | ||
370 | <para> | |
371 | ata_port_freeze() is called when HSM violations or some other | |
372 | condition disrupts normal operation of the port. A frozen port | |
373 | is not allowed to perform any operation until the port is | |
374 | thawed, which usually follows a successful reset. | |
375 | </para> | |
376 | ||
377 | <para> | |
378 | The optional ->freeze() callback can be used for freezing the port | |
379 | hardware-wise (e.g. mask interrupt and stop DMA engine). If a | |
380 | port cannot be frozen hardware-wise, the interrupt handler | |
381 | must ack and clear interrupts unconditionally while the port | |
382 | is frozen. | |
383 | </para> | |
384 | <para> | |
385 | The optional ->thaw() callback is called to perform the opposite of ->freeze(): | |
386 | prepare the port for normal operation once again. Unmask interrupts, | |
387 | start DMA engine, etc. | |
388 | </para> | |
389 | ||
390 | <programlisting> | |
391 | void (*error_handler) (struct ata_port *ap); | |
392 | </programlisting> | |
393 | ||
394 | <para> | |
395 | ->error_handler() is a driver's hook into probe, hotplug, and recovery | |
396 | and other exceptional conditions. The primary responsibility of an | |
397 | implementation is to call ata_do_eh() or ata_bmdma_drive_eh() with a set | |
398 | of EH hooks as arguments: | |
399 | </para> | |
400 | ||
401 | <para> | |
402 | 'prereset' hook (may be NULL) is called during an EH reset, before any other actions | |
403 | are taken. | |
404 | </para> | |
405 | ||
406 | <para> | |
407 | 'postreset' hook (may be NULL) is called after the EH reset is performed. Based on | |
408 | existing conditions, severity of the problem, and hardware capabilities, | |
409 | </para> | |
410 | ||
411 | <para> | |
412 | Either 'softreset' (may be NULL) or 'hardreset' (may be NULL) will be | |
413 | called to perform the low-level EH reset. | |
414 | </para> | |
415 | ||
416 | <programlisting> | |
417 | void (*post_internal_cmd) (struct ata_queued_cmd *qc); | |
1da177e4 LT |
418 | </programlisting> |
419 | ||
420 | <para> | |
bf717b11 JG |
421 | Perform any hardware-specific actions necessary to finish processing |
422 | after executing a probe-time or EH-time command via ata_exec_internal(). | |
1da177e4 LT |
423 | </para> |
424 | ||
92bab26b JG |
425 | </sect2> |
426 | ||
427 | <sect2><title>Hardware interrupt handling</title> | |
1da177e4 LT |
428 | <programlisting> |
429 | irqreturn_t (*irq_handler)(int, void *, struct pt_regs *); | |
430 | void (*irq_clear) (struct ata_port *); | |
431 | </programlisting> | |
432 | ||
433 | <para> | |
434 | ->irq_handler is the interrupt handling routine registered with | |
435 | the system, by libata. ->irq_clear is called during probe just | |
436 | before the interrupt handler is registered, to be sure hardware | |
437 | is quiet. | |
438 | </para> | |
8b2af8f0 EF |
439 | <para> |
440 | The second argument, dev_instance, should be cast to a pointer | |
441 | to struct ata_host_set. | |
442 | </para> | |
443 | <para> | |
444 | Most legacy IDE drivers use ata_interrupt() for the | |
445 | irq_handler hook, which scans all ports in the host_set, | |
446 | determines which queued command was active (if any), and calls | |
447 | ata_host_intr(ap,qc). | |
448 | </para> | |
449 | <para> | |
450 | Most legacy IDE drivers use ata_bmdma_irq_clear() for the | |
451 | irq_clear() hook, which simply clears the interrupt and error | |
452 | flags in the DMA status register. | |
453 | </para> | |
1da177e4 | 454 | |
92bab26b JG |
455 | </sect2> |
456 | ||
457 | <sect2><title>SATA phy read/write</title> | |
1da177e4 | 458 | <programlisting> |
110dd8f1 JB |
459 | int (*scr_read) (struct ata_port *ap, unsigned int sc_reg, |
460 | u32 *val); | |
461 | int (*scr_write) (struct ata_port *ap, unsigned int sc_reg, | |
1da177e4 LT |
462 | u32 val); |
463 | </programlisting> | |
464 | ||
465 | <para> | |
466 | Read and write standard SATA phy registers. Currently only used | |
467 | if ->phy_reset hook called the sata_phy_reset() helper function. | |
8b2af8f0 | 468 | sc_reg is one of SCR_STATUS, SCR_CONTROL, SCR_ERROR, or SCR_ACTIVE. |
1da177e4 LT |
469 | </para> |
470 | ||
92bab26b JG |
471 | </sect2> |
472 | ||
473 | <sect2><title>Init and shutdown</title> | |
1da177e4 LT |
474 | <programlisting> |
475 | int (*port_start) (struct ata_port *ap); | |
476 | void (*port_stop) (struct ata_port *ap); | |
477 | void (*host_stop) (struct ata_host_set *host_set); | |
478 | </programlisting> | |
479 | ||
480 | <para> | |
481 | ->port_start() is called just after the data structures for each | |
482 | port are initialized. Typically this is used to alloc per-port | |
483 | DMA buffers / tables / rings, enable DMA engines, and similar | |
8b2af8f0 EF |
484 | tasks. Some drivers also use this entry point as a chance to |
485 | allocate driver-private memory for ap->private_data. | |
486 | </para> | |
487 | <para> | |
488 | Many drivers use ata_port_start() as this hook or call | |
489 | it from their own port_start() hooks. ata_port_start() | |
490 | allocates space for a legacy IDE PRD table and returns. | |
1da177e4 LT |
491 | </para> |
492 | <para> | |
1da177e4 LT |
493 | ->port_stop() is called after ->host_stop(). It's sole function |
494 | is to release DMA/memory resources, now that they are no longer | |
8b2af8f0 EF |
495 | actively being used. Many drivers also free driver-private |
496 | data from port at this time. | |
497 | </para> | |
498 | <para> | |
499 | Many drivers use ata_port_stop() as this hook, which frees the | |
500 | PRD table. | |
1da177e4 | 501 | </para> |
780a87f7 JG |
502 | <para> |
503 | ->host_stop() is called after all ->port_stop() calls | |
504 | have completed. The hook must finalize hardware shutdown, release DMA | |
505 | and other resources, etc. | |
8b2af8f0 | 506 | This hook may be specified as NULL, in which case it is not called. |
780a87f7 | 507 | </para> |
1da177e4 | 508 | |
92bab26b JG |
509 | </sect2> |
510 | ||
1da177e4 | 511 | </sect1> |
a1213499 JG |
512 | </chapter> |
513 | ||
514 | <chapter id="libataEH"> | |
bfd00722 TH |
515 | <title>Error handling</title> |
516 | ||
517 | <para> | |
518 | This chapter describes how errors are handled under libata. | |
519 | Readers are advised to read SCSI EH | |
520 | (Documentation/scsi/scsi_eh.txt) and ATA exceptions doc first. | |
521 | </para> | |
522 | ||
a1213499 | 523 | <sect1><title>Origins of commands</title> |
bfd00722 TH |
524 | <para> |
525 | In libata, a command is represented with struct ata_queued_cmd | |
526 | or qc. qc's are preallocated during port initialization and | |
527 | repetitively used for command executions. Currently only one | |
528 | qc is allocated per port but yet-to-be-merged NCQ branch | |
529 | allocates one for each tag and maps each qc to NCQ tag 1-to-1. | |
530 | </para> | |
531 | <para> | |
532 | libata commands can originate from two sources - libata itself | |
533 | and SCSI midlayer. libata internal commands are used for | |
534 | initialization and error handling. All normal blk requests | |
535 | and commands for SCSI emulation are passed as SCSI commands | |
536 | through queuecommand callback of SCSI host template. | |
537 | </para> | |
a1213499 | 538 | </sect1> |
bfd00722 | 539 | |
a1213499 | 540 | <sect1><title>How commands are issued</title> |
bfd00722 TH |
541 | |
542 | <variablelist> | |
543 | ||
544 | <varlistentry><term>Internal commands</term> | |
545 | <listitem> | |
546 | <para> | |
547 | First, qc is allocated and initialized using | |
548 | ata_qc_new_init(). Although ata_qc_new_init() doesn't | |
549 | implement any wait or retry mechanism when qc is not | |
550 | available, internal commands are currently issued only during | |
551 | initialization and error recovery, so no other command is | |
552 | active and allocation is guaranteed to succeed. | |
553 | </para> | |
554 | <para> | |
555 | Once allocated qc's taskfile is initialized for the command to | |
556 | be executed. qc currently has two mechanisms to notify | |
557 | completion. One is via qc->complete_fn() callback and the | |
558 | other is completion qc->waiting. qc->complete_fn() callback | |
559 | is the asynchronous path used by normal SCSI translated | |
560 | commands and qc->waiting is the synchronous (issuer sleeps in | |
561 | process context) path used by internal commands. | |
562 | </para> | |
563 | <para> | |
564 | Once initialization is complete, host_set lock is acquired | |
565 | and the qc is issued. | |
566 | </para> | |
567 | </listitem> | |
568 | </varlistentry> | |
569 | ||
570 | <varlistentry><term>SCSI commands</term> | |
571 | <listitem> | |
572 | <para> | |
573 | All libata drivers use ata_scsi_queuecmd() as | |
574 | hostt->queuecommand callback. scmds can either be simulated | |
575 | or translated. No qc is involved in processing a simulated | |
576 | scmd. The result is computed right away and the scmd is | |
577 | completed. | |
578 | </para> | |
579 | <para> | |
580 | For a translated scmd, ata_qc_new_init() is invoked to | |
581 | allocate a qc and the scmd is translated into the qc. SCSI | |
582 | midlayer's completion notification function pointer is stored | |
583 | into qc->scsidone. | |
584 | </para> | |
585 | <para> | |
586 | qc->complete_fn() callback is used for completion | |
587 | notification. ATA commands use ata_scsi_qc_complete() while | |
588 | ATAPI commands use atapi_qc_complete(). Both functions end up | |
589 | calling qc->scsidone to notify upper layer when the qc is | |
590 | finished. After translation is completed, the qc is issued | |
591 | with ata_qc_issue(). | |
592 | </para> | |
593 | <para> | |
594 | Note that SCSI midlayer invokes hostt->queuecommand while | |
595 | holding host_set lock, so all above occur while holding | |
596 | host_set lock. | |
597 | </para> | |
598 | </listitem> | |
599 | </varlistentry> | |
600 | ||
601 | </variablelist> | |
a1213499 | 602 | </sect1> |
bfd00722 | 603 | |
a1213499 | 604 | <sect1><title>How commands are processed</title> |
bfd00722 TH |
605 | <para> |
606 | Depending on which protocol and which controller are used, | |
607 | commands are processed differently. For the purpose of | |
608 | discussion, a controller which uses taskfile interface and all | |
609 | standard callbacks is assumed. | |
610 | </para> | |
611 | <para> | |
612 | Currently 6 ATA command protocols are used. They can be | |
613 | sorted into the following four categories according to how | |
614 | they are processed. | |
615 | </para> | |
616 | ||
617 | <variablelist> | |
618 | <varlistentry><term>ATA NO DATA or DMA</term> | |
619 | <listitem> | |
620 | <para> | |
621 | ATA_PROT_NODATA and ATA_PROT_DMA fall into this category. | |
622 | These types of commands don't require any software | |
623 | intervention once issued. Device will raise interrupt on | |
624 | completion. | |
625 | </para> | |
626 | </listitem> | |
627 | </varlistentry> | |
628 | ||
629 | <varlistentry><term>ATA PIO</term> | |
630 | <listitem> | |
631 | <para> | |
632 | ATA_PROT_PIO is in this category. libata currently | |
633 | implements PIO with polling. ATA_NIEN bit is set to turn | |
634 | off interrupt and pio_task on ata_wq performs polling and | |
635 | IO. | |
636 | </para> | |
637 | </listitem> | |
638 | </varlistentry> | |
639 | ||
640 | <varlistentry><term>ATAPI NODATA or DMA</term> | |
641 | <listitem> | |
642 | <para> | |
643 | ATA_PROT_ATAPI_NODATA and ATA_PROT_ATAPI_DMA are in this | |
644 | category. packet_task is used to poll BSY bit after | |
645 | issuing PACKET command. Once BSY is turned off by the | |
646 | device, packet_task transfers CDB and hands off processing | |
647 | to interrupt handler. | |
648 | </para> | |
649 | </listitem> | |
650 | </varlistentry> | |
651 | ||
652 | <varlistentry><term>ATAPI PIO</term> | |
653 | <listitem> | |
654 | <para> | |
655 | ATA_PROT_ATAPI is in this category. ATA_NIEN bit is set | |
656 | and, as in ATAPI NODATA or DMA, packet_task submits cdb. | |
657 | However, after submitting cdb, further processing (data | |
658 | transfer) is handed off to pio_task. | |
659 | </para> | |
660 | </listitem> | |
661 | </varlistentry> | |
662 | </variablelist> | |
a1213499 | 663 | </sect1> |
bfd00722 | 664 | |
a1213499 | 665 | <sect1><title>How commands are completed</title> |
bfd00722 TH |
666 | <para> |
667 | Once issued, all qc's are either completed with | |
668 | ata_qc_complete() or time out. For commands which are handled | |
669 | by interrupts, ata_host_intr() invokes ata_qc_complete(), and, | |
670 | for PIO tasks, pio_task invokes ata_qc_complete(). In error | |
671 | cases, packet_task may also complete commands. | |
672 | </para> | |
673 | <para> | |
674 | ata_qc_complete() does the following. | |
675 | </para> | |
676 | ||
677 | <orderedlist> | |
678 | ||
679 | <listitem> | |
680 | <para> | |
681 | DMA memory is unmapped. | |
682 | </para> | |
683 | </listitem> | |
684 | ||
685 | <listitem> | |
686 | <para> | |
687 | ATA_QCFLAG_ACTIVE is clared from qc->flags. | |
688 | </para> | |
689 | </listitem> | |
690 | ||
691 | <listitem> | |
692 | <para> | |
693 | qc->complete_fn() callback is invoked. If the return value of | |
694 | the callback is not zero. Completion is short circuited and | |
695 | ata_qc_complete() returns. | |
696 | </para> | |
697 | </listitem> | |
698 | ||
699 | <listitem> | |
700 | <para> | |
701 | __ata_qc_complete() is called, which does | |
702 | <orderedlist> | |
703 | ||
704 | <listitem> | |
705 | <para> | |
706 | qc->flags is cleared to zero. | |
707 | </para> | |
708 | </listitem> | |
709 | ||
710 | <listitem> | |
711 | <para> | |
712 | ap->active_tag and qc->tag are poisoned. | |
713 | </para> | |
714 | </listitem> | |
715 | ||
716 | <listitem> | |
717 | <para> | |
718 | qc->waiting is claread & completed (in that order). | |
719 | </para> | |
720 | </listitem> | |
721 | ||
722 | <listitem> | |
723 | <para> | |
724 | qc is deallocated by clearing appropriate bit in ap->qactive. | |
725 | </para> | |
726 | </listitem> | |
727 | ||
728 | </orderedlist> | |
729 | </para> | |
730 | </listitem> | |
731 | ||
732 | </orderedlist> | |
733 | ||
734 | <para> | |
735 | So, it basically notifies upper layer and deallocates qc. One | |
736 | exception is short-circuit path in #3 which is used by | |
737 | atapi_qc_complete(). | |
738 | </para> | |
739 | <para> | |
740 | For all non-ATAPI commands, whether it fails or not, almost | |
741 | the same code path is taken and very little error handling | |
742 | takes place. A qc is completed with success status if it | |
743 | succeeded, with failed status otherwise. | |
744 | </para> | |
745 | <para> | |
746 | However, failed ATAPI commands require more handling as | |
747 | REQUEST SENSE is needed to acquire sense data. If an ATAPI | |
748 | command fails, ata_qc_complete() is invoked with error status, | |
749 | which in turn invokes atapi_qc_complete() via | |
750 | qc->complete_fn() callback. | |
751 | </para> | |
752 | <para> | |
753 | This makes atapi_qc_complete() set scmd->result to | |
754 | SAM_STAT_CHECK_CONDITION, complete the scmd and return 1. As | |
755 | the sense data is empty but scmd->result is CHECK CONDITION, | |
756 | SCSI midlayer will invoke EH for the scmd, and returning 1 | |
757 | makes ata_qc_complete() to return without deallocating the qc. | |
758 | This leads us to ata_scsi_error() with partially completed qc. | |
759 | </para> | |
760 | ||
a1213499 | 761 | </sect1> |
bfd00722 | 762 | |
a1213499 | 763 | <sect1><title>ata_scsi_error()</title> |
bfd00722 | 764 | <para> |
9227c33d | 765 | ata_scsi_error() is the current transportt->eh_strategy_handler() |
bfd00722 TH |
766 | for libata. As discussed above, this will be entered in two |
767 | cases - timeout and ATAPI error completion. This function | |
768 | calls low level libata driver's eng_timeout() callback, the | |
769 | standard callback for which is ata_eng_timeout(). It checks | |
770 | if a qc is active and calls ata_qc_timeout() on the qc if so. | |
771 | Actual error handling occurs in ata_qc_timeout(). | |
772 | </para> | |
773 | <para> | |
774 | If EH is invoked for timeout, ata_qc_timeout() stops BMDMA and | |
775 | completes the qc. Note that as we're currently in EH, we | |
776 | cannot call scsi_done. As described in SCSI EH doc, a | |
777 | recovered scmd should be either retried with | |
778 | scsi_queue_insert() or finished with scsi_finish_command(). | |
779 | Here, we override qc->scsidone with scsi_finish_command() and | |
780 | calls ata_qc_complete(). | |
781 | </para> | |
782 | <para> | |
783 | If EH is invoked due to a failed ATAPI qc, the qc here is | |
784 | completed but not deallocated. The purpose of this | |
785 | half-completion is to use the qc as place holder to make EH | |
786 | code reach this place. This is a bit hackish, but it works. | |
787 | </para> | |
788 | <para> | |
789 | Once control reaches here, the qc is deallocated by invoking | |
790 | __ata_qc_complete() explicitly. Then, internal qc for REQUEST | |
791 | SENSE is issued. Once sense data is acquired, scmd is | |
792 | finished by directly invoking scsi_finish_command() on the | |
793 | scmd. Note that as we already have completed and deallocated | |
794 | the qc which was associated with the scmd, we don't need | |
795 | to/cannot call ata_qc_complete() again. | |
796 | </para> | |
797 | ||
a1213499 | 798 | </sect1> |
bfd00722 | 799 | |
a1213499 | 800 | <sect1><title>Problems with the current EH</title> |
bfd00722 TH |
801 | |
802 | <itemizedlist> | |
803 | ||
804 | <listitem> | |
805 | <para> | |
806 | Error representation is too crude. Currently any and all | |
807 | error conditions are represented with ATA STATUS and ERROR | |
808 | registers. Errors which aren't ATA device errors are treated | |
809 | as ATA device errors by setting ATA_ERR bit. Better error | |
810 | descriptor which can properly represent ATA and other | |
811 | errors/exceptions is needed. | |
812 | </para> | |
813 | </listitem> | |
814 | ||
815 | <listitem> | |
816 | <para> | |
817 | When handling timeouts, no action is taken to make device | |
818 | forget about the timed out command and ready for new commands. | |
819 | </para> | |
820 | </listitem> | |
821 | ||
822 | <listitem> | |
823 | <para> | |
824 | EH handling via ata_scsi_error() is not properly protected | |
825 | from usual command processing. On EH entrance, the device is | |
826 | not in quiescent state. Timed out commands may succeed or | |
827 | fail any time. pio_task and atapi_task may still be running. | |
828 | </para> | |
829 | </listitem> | |
830 | ||
831 | <listitem> | |
832 | <para> | |
833 | Too weak error recovery. Devices / controllers causing HSM | |
834 | mismatch errors and other errors quite often require reset to | |
835 | return to known state. Also, advanced error handling is | |
836 | necessary to support features like NCQ and hotplug. | |
837 | </para> | |
838 | </listitem> | |
839 | ||
840 | <listitem> | |
841 | <para> | |
842 | ATA errors are directly handled in the interrupt handler and | |
843 | PIO errors in pio_task. This is problematic for advanced | |
844 | error handling for the following reasons. | |
845 | </para> | |
846 | <para> | |
847 | First, advanced error handling often requires context and | |
848 | internal qc execution. | |
849 | </para> | |
850 | <para> | |
851 | Second, even a simple failure (say, CRC error) needs | |
852 | information gathering and could trigger complex error handling | |
853 | (say, resetting & reconfiguring). Having multiple code | |
854 | paths to gather information, enter EH and trigger actions | |
855 | makes life painful. | |
856 | </para> | |
857 | <para> | |
858 | Third, scattered EH code makes implementing low level drivers | |
859 | difficult. Low level drivers override libata callbacks. If | |
860 | EH is scattered over several places, each affected callbacks | |
861 | should perform its part of error handling. This can be error | |
862 | prone and painful. | |
863 | </para> | |
864 | </listitem> | |
865 | ||
866 | </itemizedlist> | |
a1213499 | 867 | </sect1> |
1da177e4 LT |
868 | </chapter> |
869 | ||
870 | <chapter id="libataExt"> | |
871 | <title>libata Library</title> | |
58707cce | 872 | !Edrivers/ata/libata-core.c |
1da177e4 LT |
873 | </chapter> |
874 | ||
875 | <chapter id="libataInt"> | |
876 | <title>libata Core Internals</title> | |
58707cce | 877 | !Idrivers/ata/libata-core.c |
1da177e4 LT |
878 | </chapter> |
879 | ||
880 | <chapter id="libataScsiInt"> | |
881 | <title>libata SCSI translation/emulation</title> | |
58707cce HK |
882 | !Edrivers/ata/libata-scsi.c |
883 | !Idrivers/ata/libata-scsi.c | |
1da177e4 LT |
884 | </chapter> |
885 | ||
fe998aa7 | 886 | <chapter id="ataExceptions"> |
7db51fbe | 887 | <title>ATA errors and exceptions</title> |
fe998aa7 TH |
888 | |
889 | <para> | |
890 | This chapter tries to identify what error/exception conditions exist | |
891 | for ATA/ATAPI devices and describe how they should be handled in | |
892 | implementation-neutral way. | |
893 | </para> | |
894 | ||
895 | <para> | |
896 | The term 'error' is used to describe conditions where either an | |
897 | explicit error condition is reported from device or a command has | |
898 | timed out. | |
899 | </para> | |
900 | ||
901 | <para> | |
902 | The term 'exception' is either used to describe exceptional | |
903 | conditions which are not errors (say, power or hotplug events), or | |
904 | to describe both errors and non-error exceptional conditions. Where | |
905 | explicit distinction between error and exception is necessary, the | |
906 | term 'non-error exception' is used. | |
907 | </para> | |
908 | ||
909 | <sect1 id="excat"> | |
910 | <title>Exception categories</title> | |
911 | <para> | |
912 | Exceptions are described primarily with respect to legacy | |
913 | taskfile + bus master IDE interface. If a controller provides | |
914 | other better mechanism for error reporting, mapping those into | |
915 | categories described below shouldn't be difficult. | |
916 | </para> | |
917 | ||
918 | <para> | |
919 | In the following sections, two recovery actions - reset and | |
920 | reconfiguring transport - are mentioned. These are described | |
921 | further in <xref linkend="exrec"/>. | |
922 | </para> | |
923 | ||
924 | <sect2 id="excatHSMviolation"> | |
925 | <title>HSM violation</title> | |
926 | <para> | |
927 | This error is indicated when STATUS value doesn't match HSM | |
928 | requirement during issuing or excution any ATA/ATAPI command. | |
929 | </para> | |
930 | ||
931 | <itemizedlist> | |
932 | <title>Examples</title> | |
933 | ||
934 | <listitem> | |
935 | <para> | |
936 | ATA_STATUS doesn't contain !BSY && DRDY && !DRQ while trying | |
937 | to issue a command. | |
938 | </para> | |
939 | </listitem> | |
940 | ||
941 | <listitem> | |
942 | <para> | |
943 | !BSY && !DRQ during PIO data transfer. | |
944 | </para> | |
945 | </listitem> | |
946 | ||
947 | <listitem> | |
948 | <para> | |
949 | DRQ on command completion. | |
950 | </para> | |
951 | </listitem> | |
952 | ||
953 | <listitem> | |
954 | <para> | |
955 | !BSY && ERR after CDB tranfer starts but before the | |
956 | last byte of CDB is transferred. ATA/ATAPI standard states | |
957 | that "The device shall not terminate the PACKET command | |
958 | with an error before the last byte of the command packet has | |
959 | been written" in the error outputs description of PACKET | |
960 | command and the state diagram doesn't include such | |
961 | transitions. | |
962 | </para> | |
963 | </listitem> | |
964 | ||
965 | </itemizedlist> | |
966 | ||
967 | <para> | |
968 | In these cases, HSM is violated and not much information | |
969 | regarding the error can be acquired from STATUS or ERROR | |
970 | register. IOW, this error can be anything - driver bug, | |
971 | faulty device, controller and/or cable. | |
972 | </para> | |
973 | ||
974 | <para> | |
975 | As HSM is violated, reset is necessary to restore known state. | |
976 | Reconfiguring transport for lower speed might be helpful too | |
977 | as transmission errors sometimes cause this kind of errors. | |
978 | </para> | |
979 | </sect2> | |
980 | ||
981 | <sect2 id="excatDevErr"> | |
982 | <title>ATA/ATAPI device error (non-NCQ / non-CHECK CONDITION)</title> | |
983 | ||
984 | <para> | |
985 | These are errors detected and reported by ATA/ATAPI devices | |
986 | indicating device problems. For this type of errors, STATUS | |
987 | and ERROR register values are valid and describe error | |
988 | condition. Note that some of ATA bus errors are detected by | |
989 | ATA/ATAPI devices and reported using the same mechanism as | |
990 | device errors. Those cases are described later in this | |
991 | section. | |
992 | </para> | |
993 | ||
994 | <para> | |
995 | For ATA commands, this type of errors are indicated by !BSY | |
996 | && ERR during command execution and on completion. | |
997 | </para> | |
998 | ||
999 | <para>For ATAPI commands,</para> | |
1000 | ||
1001 | <itemizedlist> | |
1002 | ||
1003 | <listitem> | |
1004 | <para> | |
1005 | !BSY && ERR && ABRT right after issuing PACKET | |
1006 | indicates that PACKET command is not supported and falls in | |
1007 | this category. | |
1008 | </para> | |
1009 | </listitem> | |
1010 | ||
1011 | <listitem> | |
1012 | <para> | |
1013 | !BSY && ERR(==CHK) && !ABRT after the last | |
1014 | byte of CDB is transferred indicates CHECK CONDITION and | |
1015 | doesn't fall in this category. | |
1016 | </para> | |
1017 | </listitem> | |
1018 | ||
1019 | <listitem> | |
1020 | <para> | |
1021 | !BSY && ERR(==CHK) && ABRT after the last byte | |
1022 | of CDB is transferred *probably* indicates CHECK CONDITION and | |
1023 | doesn't fall in this category. | |
1024 | </para> | |
1025 | </listitem> | |
1026 | ||
1027 | </itemizedlist> | |
1028 | ||
1029 | <para> | |
1030 | Of errors detected as above, the followings are not ATA/ATAPI | |
1031 | device errors but ATA bus errors and should be handled | |
1032 | according to <xref linkend="excatATAbusErr"/>. | |
1033 | </para> | |
1034 | ||
1035 | <variablelist> | |
1036 | ||
1037 | <varlistentry> | |
1038 | <term>CRC error during data transfer</term> | |
1039 | <listitem> | |
1040 | <para> | |
1041 | This is indicated by ICRC bit in the ERROR register and | |
1042 | means that corruption occurred during data transfer. Upto | |
1043 | ATA/ATAPI-7, the standard specifies that this bit is only | |
1044 | applicable to UDMA transfers but ATA/ATAPI-8 draft revision | |
1045 | 1f says that the bit may be applicable to multiword DMA and | |
1046 | PIO. | |
1047 | </para> | |
1048 | </listitem> | |
1049 | </varlistentry> | |
1050 | ||
1051 | <varlistentry> | |
1052 | <term>ABRT error during data transfer or on completion</term> | |
1053 | <listitem> | |
1054 | <para> | |
1055 | Upto ATA/ATAPI-7, the standard specifies that ABRT could be | |
1056 | set on ICRC errors and on cases where a device is not able | |
1057 | to complete a command. Combined with the fact that MWDMA | |
1058 | and PIO transfer errors aren't allowed to use ICRC bit upto | |
1059 | ATA/ATAPI-7, it seems to imply that ABRT bit alone could | |
1060 | indicate tranfer errors. | |
1061 | </para> | |
1062 | <para> | |
1063 | However, ATA/ATAPI-8 draft revision 1f removes the part | |
1064 | that ICRC errors can turn on ABRT. So, this is kind of | |
1065 | gray area. Some heuristics are needed here. | |
1066 | </para> | |
1067 | </listitem> | |
1068 | </varlistentry> | |
1069 | ||
1070 | </variablelist> | |
1071 | ||
1072 | <para> | |
1073 | ATA/ATAPI device errors can be further categorized as follows. | |
1074 | </para> | |
1075 | ||
1076 | <variablelist> | |
1077 | ||
1078 | <varlistentry> | |
1079 | <term>Media errors</term> | |
1080 | <listitem> | |
1081 | <para> | |
1082 | This is indicated by UNC bit in the ERROR register. ATA | |
1083 | devices reports UNC error only after certain number of | |
1084 | retries cannot recover the data, so there's nothing much | |
1085 | else to do other than notifying upper layer. | |
1086 | </para> | |
1087 | <para> | |
1088 | READ and WRITE commands report CHS or LBA of the first | |
1089 | failed sector but ATA/ATAPI standard specifies that the | |
1090 | amount of transferred data on error completion is | |
1091 | indeterminate, so we cannot assume that sectors preceding | |
1092 | the failed sector have been transferred and thus cannot | |
1093 | complete those sectors successfully as SCSI does. | |
1094 | </para> | |
1095 | </listitem> | |
1096 | </varlistentry> | |
1097 | ||
1098 | <varlistentry> | |
1099 | <term>Media changed / media change requested error</term> | |
1100 | <listitem> | |
1101 | <para> | |
1102 | <<TODO: fill here>> | |
1103 | </para> | |
1104 | </listitem> | |
1105 | </varlistentry> | |
1106 | ||
1107 | <varlistentry><term>Address error</term> | |
1108 | <listitem> | |
1109 | <para> | |
1110 | This is indicated by IDNF bit in the ERROR register. | |
1111 | Report to upper layer. | |
1112 | </para> | |
1113 | </listitem> | |
1114 | </varlistentry> | |
1115 | ||
1116 | <varlistentry><term>Other errors</term> | |
1117 | <listitem> | |
1118 | <para> | |
1119 | This can be invalid command or parameter indicated by ABRT | |
1120 | ERROR bit or some other error condition. Note that ABRT | |
1121 | bit can indicate a lot of things including ICRC and Address | |
1122 | errors. Heuristics needed. | |
1123 | </para> | |
1124 | </listitem> | |
1125 | </varlistentry> | |
1126 | ||
1127 | </variablelist> | |
1128 | ||
1129 | <para> | |
1130 | Depending on commands, not all STATUS/ERROR bits are | |
1131 | applicable. These non-applicable bits are marked with | |
1132 | "na" in the output descriptions but upto ATA/ATAPI-7 | |
1133 | no definition of "na" can be found. However, | |
1134 | ATA/ATAPI-8 draft revision 1f describes "N/A" as | |
1135 | follows. | |
1136 | </para> | |
1137 | ||
1138 | <blockquote> | |
1139 | <variablelist> | |
1140 | <varlistentry><term>3.2.3.3a N/A</term> | |
1141 | <listitem> | |
1142 | <para> | |
1143 | A keyword the indicates a field has no defined value in | |
1144 | this standard and should not be checked by the host or | |
1145 | device. N/A fields should be cleared to zero. | |
1146 | </para> | |
1147 | </listitem> | |
1148 | </varlistentry> | |
1149 | </variablelist> | |
1150 | </blockquote> | |
1151 | ||
1152 | <para> | |
1153 | So, it seems reasonable to assume that "na" bits are | |
1154 | cleared to zero by devices and thus need no explicit masking. | |
1155 | </para> | |
1156 | ||
1157 | </sect2> | |
1158 | ||
1159 | <sect2 id="excatATAPIcc"> | |
1160 | <title>ATAPI device CHECK CONDITION</title> | |
1161 | ||
1162 | <para> | |
1163 | ATAPI device CHECK CONDITION error is indicated by set CHK bit | |
1164 | (ERR bit) in the STATUS register after the last byte of CDB is | |
1165 | transferred for a PACKET command. For this kind of errors, | |
1166 | sense data should be acquired to gather information regarding | |
1167 | the errors. REQUEST SENSE packet command should be used to | |
1168 | acquire sense data. | |
1169 | </para> | |
1170 | ||
1171 | <para> | |
1172 | Once sense data is acquired, this type of errors can be | |
1173 | handled similary to other SCSI errors. Note that sense data | |
1174 | may indicate ATA bus error (e.g. Sense Key 04h HARDWARE ERROR | |
1175 | && ASC/ASCQ 47h/00h SCSI PARITY ERROR). In such | |
1176 | cases, the error should be considered as an ATA bus error and | |
1177 | handled according to <xref linkend="excatATAbusErr"/>. | |
1178 | </para> | |
1179 | ||
1180 | </sect2> | |
1181 | ||
1182 | <sect2 id="excatNCQerr"> | |
1183 | <title>ATA device error (NCQ)</title> | |
1184 | ||
1185 | <para> | |
1186 | NCQ command error is indicated by cleared BSY and set ERR bit | |
1187 | during NCQ command phase (one or more NCQ commands | |
1188 | outstanding). Although STATUS and ERROR registers will | |
1189 | contain valid values describing the error, READ LOG EXT is | |
1190 | required to clear the error condition, determine which command | |
1191 | has failed and acquire more information. | |
1192 | </para> | |
1193 | ||
1194 | <para> | |
1195 | READ LOG EXT Log Page 10h reports which tag has failed and | |
1196 | taskfile register values describing the error. With this | |
1197 | information the failed command can be handled as a normal ATA | |
1198 | command error as in <xref linkend="excatDevErr"/> and all | |
1199 | other in-flight commands must be retried. Note that this | |
1200 | retry should not be counted - it's likely that commands | |
1201 | retried this way would have completed normally if it were not | |
1202 | for the failed command. | |
1203 | </para> | |
1204 | ||
1205 | <para> | |
1206 | Note that ATA bus errors can be reported as ATA device NCQ | |
1207 | errors. This should be handled as described in <xref | |
1208 | linkend="excatATAbusErr"/>. | |
1209 | </para> | |
1210 | ||
1211 | <para> | |
1212 | If READ LOG EXT Log Page 10h fails or reports NQ, we're | |
1213 | thoroughly screwed. This condition should be treated | |
1214 | according to <xref linkend="excatHSMviolation"/>. | |
1215 | </para> | |
1216 | ||
1217 | </sect2> | |
1218 | ||
1219 | <sect2 id="excatATAbusErr"> | |
1220 | <title>ATA bus error</title> | |
1221 | ||
1222 | <para> | |
1223 | ATA bus error means that data corruption occurred during | |
1224 | transmission over ATA bus (SATA or PATA). This type of errors | |
1225 | can be indicated by | |
1226 | </para> | |
1227 | ||
1228 | <itemizedlist> | |
1229 | ||
1230 | <listitem> | |
1231 | <para> | |
1232 | ICRC or ABRT error as described in <xref linkend="excatDevErr"/>. | |
1233 | </para> | |
1234 | </listitem> | |
1235 | ||
1236 | <listitem> | |
1237 | <para> | |
1238 | Controller-specific error completion with error information | |
1239 | indicating transmission error. | |
1240 | </para> | |
1241 | </listitem> | |
1242 | ||
1243 | <listitem> | |
1244 | <para> | |
1245 | On some controllers, command timeout. In this case, there may | |
1246 | be a mechanism to determine that the timeout is due to | |
1247 | transmission error. | |
1248 | </para> | |
1249 | </listitem> | |
1250 | ||
1251 | <listitem> | |
1252 | <para> | |
1253 | Unknown/random errors, timeouts and all sorts of weirdities. | |
1254 | </para> | |
1255 | </listitem> | |
1256 | ||
1257 | </itemizedlist> | |
1258 | ||
1259 | <para> | |
1260 | As described above, transmission errors can cause wide variety | |
1261 | of symptoms ranging from device ICRC error to random device | |
1262 | lockup, and, for many cases, there is no way to tell if an | |
1263 | error condition is due to transmission error or not; | |
1264 | therefore, it's necessary to employ some kind of heuristic | |
1265 | when dealing with errors and timeouts. For example, | |
1266 | encountering repetitive ABRT errors for known supported | |
1267 | command is likely to indicate ATA bus error. | |
1268 | </para> | |
1269 | ||
1270 | <para> | |
1271 | Once it's determined that ATA bus errors have possibly | |
1272 | occurred, lowering ATA bus transmission speed is one of | |
1273 | actions which may alleviate the problem. See <xref | |
1274 | linkend="exrecReconf"/> for more information. | |
1275 | </para> | |
1276 | ||
1277 | </sect2> | |
1278 | ||
1279 | <sect2 id="excatPCIbusErr"> | |
1280 | <title>PCI bus error</title> | |
1281 | ||
1282 | <para> | |
1283 | Data corruption or other failures during transmission over PCI | |
1284 | (or other system bus). For standard BMDMA, this is indicated | |
1285 | by Error bit in the BMDMA Status register. This type of | |
1286 | errors must be logged as it indicates something is very wrong | |
1287 | with the system. Resetting host controller is recommended. | |
1288 | </para> | |
1289 | ||
1290 | </sect2> | |
1291 | ||
1292 | <sect2 id="excatLateCompletion"> | |
1293 | <title>Late completion</title> | |
1294 | ||
1295 | <para> | |
1296 | This occurs when timeout occurs and the timeout handler finds | |
1297 | out that the timed out command has completed successfully or | |
1298 | with error. This is usually caused by lost interrupts. This | |
1299 | type of errors must be logged. Resetting host controller is | |
1300 | recommended. | |
1301 | </para> | |
1302 | ||
1303 | </sect2> | |
1304 | ||
1305 | <sect2 id="excatUnknown"> | |
1306 | <title>Unknown error (timeout)</title> | |
1307 | ||
1308 | <para> | |
1309 | This is when timeout occurs and the command is still | |
1310 | processing or the host and device are in unknown state. When | |
1311 | this occurs, HSM could be in any valid or invalid state. To | |
1312 | bring the device to known state and make it forget about the | |
1313 | timed out command, resetting is necessary. The timed out | |
1314 | command may be retried. | |
1315 | </para> | |
1316 | ||
1317 | <para> | |
1318 | Timeouts can also be caused by transmission errors. Refer to | |
1319 | <xref linkend="excatATAbusErr"/> for more details. | |
1320 | </para> | |
1321 | ||
1322 | </sect2> | |
1323 | ||
1324 | <sect2 id="excatHoplugPM"> | |
1325 | <title>Hotplug and power management exceptions</title> | |
1326 | ||
1327 | <para> | |
1328 | <<TODO: fill here>> | |
1329 | </para> | |
1330 | ||
1331 | </sect2> | |
1332 | ||
1333 | </sect1> | |
1334 | ||
1335 | <sect1 id="exrec"> | |
1336 | <title>EH recovery actions</title> | |
1337 | ||
1338 | <para> | |
1339 | This section discusses several important recovery actions. | |
1340 | </para> | |
1341 | ||
1342 | <sect2 id="exrecClr"> | |
1343 | <title>Clearing error condition</title> | |
1344 | ||
1345 | <para> | |
1346 | Many controllers require its error registers to be cleared by | |
1347 | error handler. Different controllers may have different | |
1348 | requirements. | |
1349 | </para> | |
1350 | ||
1351 | <para> | |
1352 | For SATA, it's strongly recommended to clear at least SError | |
1353 | register during error handling. | |
1354 | </para> | |
1355 | </sect2> | |
1356 | ||
1357 | <sect2 id="exrecRst"> | |
1358 | <title>Reset</title> | |
1359 | ||
1360 | <para> | |
1361 | During EH, resetting is necessary in the following cases. | |
1362 | </para> | |
1363 | ||
1364 | <itemizedlist> | |
1365 | ||
1366 | <listitem> | |
1367 | <para> | |
1368 | HSM is in unknown or invalid state | |
1369 | </para> | |
1370 | </listitem> | |
1371 | ||
1372 | <listitem> | |
1373 | <para> | |
1374 | HBA is in unknown or invalid state | |
1375 | </para> | |
1376 | </listitem> | |
1377 | ||
1378 | <listitem> | |
1379 | <para> | |
1380 | EH needs to make HBA/device forget about in-flight commands | |
1381 | </para> | |
1382 | </listitem> | |
1383 | ||
1384 | <listitem> | |
1385 | <para> | |
1386 | HBA/device behaves weirdly | |
1387 | </para> | |
1388 | </listitem> | |
1389 | ||
1390 | </itemizedlist> | |
1391 | ||
1392 | <para> | |
1393 | Resetting during EH might be a good idea regardless of error | |
1394 | condition to improve EH robustness. Whether to reset both or | |
1395 | either one of HBA and device depends on situation but the | |
1396 | following scheme is recommended. | |
1397 | </para> | |
1398 | ||
1399 | <itemizedlist> | |
1400 | ||
1401 | <listitem> | |
1402 | <para> | |
1403 | When it's known that HBA is in ready state but ATA/ATAPI | |
670e9f34 | 1404 | device is in unknown state, reset only device. |
fe998aa7 TH |
1405 | </para> |
1406 | </listitem> | |
1407 | ||
1408 | <listitem> | |
1409 | <para> | |
1410 | If HBA is in unknown state, reset both HBA and device. | |
1411 | </para> | |
1412 | </listitem> | |
1413 | ||
1414 | </itemizedlist> | |
1415 | ||
1416 | <para> | |
1417 | HBA resetting is implementation specific. For a controller | |
1418 | complying to taskfile/BMDMA PCI IDE, stopping active DMA | |
1419 | transaction may be sufficient iff BMDMA state is the only HBA | |
1420 | context. But even mostly taskfile/BMDMA PCI IDE complying | |
1421 | controllers may have implementation specific requirements and | |
1422 | mechanism to reset themselves. This must be addressed by | |
1423 | specific drivers. | |
1424 | </para> | |
1425 | ||
1426 | <para> | |
1427 | OTOH, ATA/ATAPI standard describes in detail ways to reset | |
1428 | ATA/ATAPI devices. | |
1429 | </para> | |
1430 | ||
1431 | <variablelist> | |
1432 | ||
1433 | <varlistentry><term>PATA hardware reset</term> | |
1434 | <listitem> | |
1435 | <para> | |
1436 | This is hardware initiated device reset signalled with | |
1437 | asserted PATA RESET- signal. There is no standard way to | |
1438 | initiate hardware reset from software although some | |
1439 | hardware provides registers that allow driver to directly | |
1440 | tweak the RESET- signal. | |
1441 | </para> | |
1442 | </listitem> | |
1443 | </varlistentry> | |
1444 | ||
1445 | <varlistentry><term>Software reset</term> | |
1446 | <listitem> | |
1447 | <para> | |
1448 | This is achieved by turning CONTROL SRST bit on for at | |
1449 | least 5us. Both PATA and SATA support it but, in case of | |
1450 | SATA, this may require controller-specific support as the | |
1451 | second Register FIS to clear SRST should be transmitted | |
1452 | while BSY bit is still set. Note that on PATA, this resets | |
1453 | both master and slave devices on a channel. | |
1454 | </para> | |
1455 | </listitem> | |
1456 | </varlistentry> | |
1457 | ||
1458 | <varlistentry><term>EXECUTE DEVICE DIAGNOSTIC command</term> | |
1459 | <listitem> | |
1460 | <para> | |
1461 | Although ATA/ATAPI standard doesn't describe exactly, EDD | |
1462 | implies some level of resetting, possibly similar level | |
1463 | with software reset. Host-side EDD protocol can be handled | |
1464 | with normal command processing and most SATA controllers | |
1465 | should be able to handle EDD's just like other commands. | |
1466 | As in software reset, EDD affects both devices on a PATA | |
1467 | bus. | |
1468 | </para> | |
1469 | <para> | |
1470 | Although EDD does reset devices, this doesn't suit error | |
1471 | handling as EDD cannot be issued while BSY is set and it's | |
1472 | unclear how it will act when device is in unknown/weird | |
1473 | state. | |
1474 | </para> | |
1475 | </listitem> | |
1476 | </varlistentry> | |
1477 | ||
1478 | <varlistentry><term>ATAPI DEVICE RESET command</term> | |
1479 | <listitem> | |
1480 | <para> | |
1481 | This is very similar to software reset except that reset | |
1482 | can be restricted to the selected device without affecting | |
1483 | the other device sharing the cable. | |
1484 | </para> | |
1485 | </listitem> | |
1486 | </varlistentry> | |
1487 | ||
1488 | <varlistentry><term>SATA phy reset</term> | |
1489 | <listitem> | |
1490 | <para> | |
1491 | This is the preferred way of resetting a SATA device. In | |
1492 | effect, it's identical to PATA hardware reset. Note that | |
1493 | this can be done with the standard SCR Control register. | |
1494 | As such, it's usually easier to implement than software | |
1495 | reset. | |
1496 | </para> | |
1497 | </listitem> | |
1498 | </varlistentry> | |
1499 | ||
1500 | </variablelist> | |
1501 | ||
1502 | <para> | |
1503 | One more thing to consider when resetting devices is that | |
1504 | resetting clears certain configuration parameters and they | |
1505 | need to be set to their previous or newly adjusted values | |
1506 | after reset. | |
1507 | </para> | |
1508 | ||
1509 | <para> | |
1510 | Parameters affected are. | |
1511 | </para> | |
1512 | ||
1513 | <itemizedlist> | |
1514 | ||
1515 | <listitem> | |
1516 | <para> | |
1517 | CHS set up with INITIALIZE DEVICE PARAMETERS (seldomly used) | |
1518 | </para> | |
1519 | </listitem> | |
1520 | ||
1521 | <listitem> | |
1522 | <para> | |
1523 | Parameters set with SET FEATURES including transfer mode setting | |
1524 | </para> | |
1525 | </listitem> | |
1526 | ||
1527 | <listitem> | |
1528 | <para> | |
1529 | Block count set with SET MULTIPLE MODE | |
1530 | </para> | |
1531 | </listitem> | |
1532 | ||
1533 | <listitem> | |
1534 | <para> | |
1535 | Other parameters (SET MAX, MEDIA LOCK...) | |
1536 | </para> | |
1537 | </listitem> | |
1538 | ||
1539 | </itemizedlist> | |
1540 | ||
1541 | <para> | |
1542 | ATA/ATAPI standard specifies that some parameters must be | |
1543 | maintained across hardware or software reset, but doesn't | |
1544 | strictly specify all of them. Always reconfiguring needed | |
1545 | parameters after reset is required for robustness. Note that | |
1546 | this also applies when resuming from deep sleep (power-off). | |
1547 | </para> | |
1548 | ||
1549 | <para> | |
1550 | Also, ATA/ATAPI standard requires that IDENTIFY DEVICE / | |
1551 | IDENTIFY PACKET DEVICE is issued after any configuration | |
1552 | parameter is updated or a hardware reset and the result used | |
1553 | for further operation. OS driver is required to implement | |
1554 | revalidation mechanism to support this. | |
1555 | </para> | |
1556 | ||
1557 | </sect2> | |
1558 | ||
1559 | <sect2 id="exrecReconf"> | |
1560 | <title>Reconfigure transport</title> | |
1561 | ||
1562 | <para> | |
1563 | For both PATA and SATA, a lot of corners are cut for cheap | |
1564 | connectors, cables or controllers and it's quite common to see | |
1565 | high transmission error rate. This can be mitigated by | |
1566 | lowering transmission speed. | |
1567 | </para> | |
1568 | ||
1569 | <para> | |
1570 | The following is a possible scheme Jeff Garzik suggested. | |
1571 | </para> | |
1572 | ||
1573 | <blockquote> | |
1574 | <para> | |
1575 | If more than $N (3?) transmission errors happen in 15 minutes, | |
1576 | </para> | |
1577 | <itemizedlist> | |
1578 | <listitem> | |
1579 | <para> | |
1580 | if SATA, decrease SATA PHY speed. if speed cannot be decreased, | |
1581 | </para> | |
1582 | </listitem> | |
1583 | <listitem> | |
1584 | <para> | |
1585 | decrease UDMA xfer speed. if at UDMA0, switch to PIO4, | |
1586 | </para> | |
1587 | </listitem> | |
1588 | <listitem> | |
1589 | <para> | |
1590 | decrease PIO xfer speed. if at PIO3, complain, but continue | |
1591 | </para> | |
1592 | </listitem> | |
1593 | </itemizedlist> | |
1594 | </blockquote> | |
1595 | ||
1596 | </sect2> | |
1597 | ||
1598 | </sect1> | |
1599 | ||
1600 | </chapter> | |
1601 | ||
1da177e4 LT |
1602 | <chapter id="PiixInt"> |
1603 | <title>ata_piix Internals</title> | |
58707cce | 1604 | !Idrivers/ata/ata_piix.c |
1da177e4 LT |
1605 | </chapter> |
1606 | ||
1607 | <chapter id="SILInt"> | |
1608 | <title>sata_sil Internals</title> | |
58707cce | 1609 | !Idrivers/ata/sata_sil.c |
1da177e4 LT |
1610 | </chapter> |
1611 | ||
0cba632b JG |
1612 | <chapter id="libataThanks"> |
1613 | <title>Thanks</title> | |
1614 | <para> | |
1615 | The bulk of the ATA knowledge comes thanks to long conversations with | |
1616 | Andre Hedrick (www.linux-ide.org), and long hours pondering the ATA | |
1617 | and SCSI specifications. | |
1618 | </para> | |
1619 | <para> | |
1620 | Thanks to Alan Cox for pointing out similarities | |
1621 | between SATA and SCSI, and in general for motivation to hack on | |
1622 | libata. | |
1623 | </para> | |
1624 | <para> | |
1625 | libata's device detection | |
1626 | method, ata_pio_devchk, and in general all the early probing was | |
1627 | based on extensive study of Hale Landis's probe/reset code in his | |
1628 | ATADRVR driver (www.ata-atapi.com). | |
1629 | </para> | |
1630 | </chapter> | |
1631 | ||
1da177e4 | 1632 | </book> |