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ae63b13b GR |
1 | /* |
2 | * I2C multiplexer driver for PCA9541 bus master selector | |
3 | * | |
4 | * Copyright (c) 2010 Ericsson AB. | |
5 | * | |
b104153e | 6 | * Author: Guenter Roeck <linux@roeck-us.net> |
ae63b13b GR |
7 | * |
8 | * Derived from: | |
9 | * pca954x.c | |
10 | * | |
11 | * Copyright (c) 2008-2009 Rodolfo Giometti <giometti@linux.it> | |
12 | * Copyright (c) 2008-2009 Eurotech S.p.A. <info@eurotech.it> | |
13 | * | |
14 | * This file is licensed under the terms of the GNU General Public | |
15 | * License version 2. This program is licensed "as is" without any | |
16 | * warranty of any kind, whether express or implied. | |
17 | */ | |
18 | ||
19 | #include <linux/module.h> | |
ae63b13b GR |
20 | #include <linux/jiffies.h> |
21 | #include <linux/delay.h> | |
22 | #include <linux/slab.h> | |
23 | #include <linux/device.h> | |
24 | #include <linux/i2c.h> | |
25 | #include <linux/i2c-mux.h> | |
26 | ||
27 | #include <linux/i2c/pca954x.h> | |
28 | ||
29 | /* | |
30 | * The PCA9541 is a bus master selector. It supports two I2C masters connected | |
31 | * to a single slave bus. | |
32 | * | |
33 | * Before each bus transaction, a master has to acquire bus ownership. After the | |
34 | * transaction is complete, bus ownership has to be released. This fits well | |
35 | * into the I2C multiplexer framework, which provides select and release | |
36 | * functions for this purpose. For this reason, this driver is modeled as | |
37 | * single-channel I2C bus multiplexer. | |
38 | * | |
39 | * This driver assumes that the two bus masters are controlled by two different | |
40 | * hosts. If a single host controls both masters, platform code has to ensure | |
41 | * that only one of the masters is instantiated at any given time. | |
42 | */ | |
43 | ||
44 | #define PCA9541_CONTROL 0x01 | |
45 | #define PCA9541_ISTAT 0x02 | |
46 | ||
47 | #define PCA9541_CTL_MYBUS (1 << 0) | |
48 | #define PCA9541_CTL_NMYBUS (1 << 1) | |
49 | #define PCA9541_CTL_BUSON (1 << 2) | |
50 | #define PCA9541_CTL_NBUSON (1 << 3) | |
51 | #define PCA9541_CTL_BUSINIT (1 << 4) | |
52 | #define PCA9541_CTL_TESTON (1 << 6) | |
53 | #define PCA9541_CTL_NTESTON (1 << 7) | |
54 | ||
55 | #define PCA9541_ISTAT_INTIN (1 << 0) | |
56 | #define PCA9541_ISTAT_BUSINIT (1 << 1) | |
57 | #define PCA9541_ISTAT_BUSOK (1 << 2) | |
58 | #define PCA9541_ISTAT_BUSLOST (1 << 3) | |
59 | #define PCA9541_ISTAT_MYTEST (1 << 6) | |
60 | #define PCA9541_ISTAT_NMYTEST (1 << 7) | |
61 | ||
62 | #define BUSON (PCA9541_CTL_BUSON | PCA9541_CTL_NBUSON) | |
63 | #define MYBUS (PCA9541_CTL_MYBUS | PCA9541_CTL_NMYBUS) | |
64 | #define mybus(x) (!((x) & MYBUS) || ((x) & MYBUS) == MYBUS) | |
65 | #define busoff(x) (!((x) & BUSON) || ((x) & BUSON) == BUSON) | |
66 | ||
67 | /* arbitration timeouts, in jiffies */ | |
68 | #define ARB_TIMEOUT (HZ / 8) /* 125 ms until forcing bus ownership */ | |
69 | #define ARB2_TIMEOUT (HZ / 4) /* 250 ms until acquisition failure */ | |
70 | ||
71 | /* arbitration retry delays, in us */ | |
72 | #define SELECT_DELAY_SHORT 50 | |
73 | #define SELECT_DELAY_LONG 1000 | |
74 | ||
75 | struct pca9541 { | |
76 | struct i2c_adapter *mux_adap; | |
77 | unsigned long select_timeout; | |
78 | unsigned long arb_timeout; | |
79 | }; | |
80 | ||
81 | static const struct i2c_device_id pca9541_id[] = { | |
82 | {"pca9541", 0}, | |
83 | {} | |
84 | }; | |
85 | ||
86 | MODULE_DEVICE_TABLE(i2c, pca9541_id); | |
87 | ||
88 | /* | |
89 | * Write to chip register. Don't use i2c_transfer()/i2c_smbus_xfer() | |
90 | * as they will try to lock the adapter a second time. | |
91 | */ | |
92 | static int pca9541_reg_write(struct i2c_client *client, u8 command, u8 val) | |
93 | { | |
94 | struct i2c_adapter *adap = client->adapter; | |
95 | int ret; | |
96 | ||
97 | if (adap->algo->master_xfer) { | |
98 | struct i2c_msg msg; | |
99 | char buf[2]; | |
100 | ||
101 | msg.addr = client->addr; | |
102 | msg.flags = 0; | |
103 | msg.len = 2; | |
104 | buf[0] = command; | |
105 | buf[1] = val; | |
106 | msg.buf = buf; | |
0a8237ae | 107 | ret = __i2c_transfer(adap, &msg, 1); |
ae63b13b GR |
108 | } else { |
109 | union i2c_smbus_data data; | |
110 | ||
111 | data.byte = val; | |
112 | ret = adap->algo->smbus_xfer(adap, client->addr, | |
113 | client->flags, | |
114 | I2C_SMBUS_WRITE, | |
115 | command, | |
116 | I2C_SMBUS_BYTE_DATA, &data); | |
117 | } | |
118 | ||
119 | return ret; | |
120 | } | |
121 | ||
122 | /* | |
123 | * Read from chip register. Don't use i2c_transfer()/i2c_smbus_xfer() | |
124 | * as they will try to lock adapter a second time. | |
125 | */ | |
126 | static int pca9541_reg_read(struct i2c_client *client, u8 command) | |
127 | { | |
128 | struct i2c_adapter *adap = client->adapter; | |
129 | int ret; | |
130 | u8 val; | |
131 | ||
132 | if (adap->algo->master_xfer) { | |
133 | struct i2c_msg msg[2] = { | |
134 | { | |
135 | .addr = client->addr, | |
136 | .flags = 0, | |
137 | .len = 1, | |
138 | .buf = &command | |
139 | }, | |
140 | { | |
141 | .addr = client->addr, | |
142 | .flags = I2C_M_RD, | |
143 | .len = 1, | |
144 | .buf = &val | |
145 | } | |
146 | }; | |
0a8237ae | 147 | ret = __i2c_transfer(adap, msg, 2); |
ae63b13b GR |
148 | if (ret == 2) |
149 | ret = val; | |
150 | else if (ret >= 0) | |
151 | ret = -EIO; | |
152 | } else { | |
153 | union i2c_smbus_data data; | |
154 | ||
155 | ret = adap->algo->smbus_xfer(adap, client->addr, | |
156 | client->flags, | |
157 | I2C_SMBUS_READ, | |
158 | command, | |
159 | I2C_SMBUS_BYTE_DATA, &data); | |
160 | if (!ret) | |
161 | ret = data.byte; | |
162 | } | |
163 | return ret; | |
164 | } | |
165 | ||
166 | /* | |
167 | * Arbitration management functions | |
168 | */ | |
169 | ||
170 | /* Release bus. Also reset NTESTON and BUSINIT if it was set. */ | |
171 | static void pca9541_release_bus(struct i2c_client *client) | |
172 | { | |
173 | int reg; | |
174 | ||
175 | reg = pca9541_reg_read(client, PCA9541_CONTROL); | |
176 | if (reg >= 0 && !busoff(reg) && mybus(reg)) | |
177 | pca9541_reg_write(client, PCA9541_CONTROL, | |
178 | (reg & PCA9541_CTL_NBUSON) >> 1); | |
179 | } | |
180 | ||
181 | /* | |
182 | * Arbitration is defined as a two-step process. A bus master can only activate | |
183 | * the slave bus if it owns it; otherwise it has to request ownership first. | |
184 | * This multi-step process ensures that access contention is resolved | |
185 | * gracefully. | |
186 | * | |
187 | * Bus Ownership Other master Action | |
188 | * state requested access | |
189 | * ---------------------------------------------------- | |
190 | * off - yes wait for arbitration timeout or | |
191 | * for other master to drop request | |
192 | * off no no take ownership | |
193 | * off yes no turn on bus | |
194 | * on yes - done | |
195 | * on no - wait for arbitration timeout or | |
196 | * for other master to release bus | |
197 | * | |
198 | * The main contention point occurs if the slave bus is off and both masters | |
199 | * request ownership at the same time. In this case, one master will turn on | |
200 | * the slave bus, believing that it owns it. The other master will request | |
201 | * bus ownership. Result is that the bus is turned on, and master which did | |
202 | * _not_ own the slave bus before ends up owning it. | |
203 | */ | |
204 | ||
205 | /* Control commands per PCA9541 datasheet */ | |
206 | static const u8 pca9541_control[16] = { | |
207 | 4, 0, 1, 5, 4, 4, 5, 5, 0, 0, 1, 1, 0, 4, 5, 1 | |
208 | }; | |
209 | ||
210 | /* | |
211 | * Channel arbitration | |
212 | * | |
213 | * Return values: | |
214 | * <0: error | |
215 | * 0 : bus not acquired | |
216 | * 1 : bus acquired | |
217 | */ | |
218 | static int pca9541_arbitrate(struct i2c_client *client) | |
219 | { | |
220 | struct pca9541 *data = i2c_get_clientdata(client); | |
221 | int reg; | |
222 | ||
223 | reg = pca9541_reg_read(client, PCA9541_CONTROL); | |
224 | if (reg < 0) | |
225 | return reg; | |
226 | ||
227 | if (busoff(reg)) { | |
228 | int istat; | |
229 | /* | |
230 | * Bus is off. Request ownership or turn it on unless | |
231 | * other master requested ownership. | |
232 | */ | |
233 | istat = pca9541_reg_read(client, PCA9541_ISTAT); | |
234 | if (!(istat & PCA9541_ISTAT_NMYTEST) | |
235 | || time_is_before_eq_jiffies(data->arb_timeout)) { | |
236 | /* | |
237 | * Other master did not request ownership, | |
238 | * or arbitration timeout expired. Take the bus. | |
239 | */ | |
240 | pca9541_reg_write(client, | |
241 | PCA9541_CONTROL, | |
242 | pca9541_control[reg & 0x0f] | |
243 | | PCA9541_CTL_NTESTON); | |
244 | data->select_timeout = SELECT_DELAY_SHORT; | |
245 | } else { | |
246 | /* | |
247 | * Other master requested ownership. | |
248 | * Set extra long timeout to give it time to acquire it. | |
249 | */ | |
250 | data->select_timeout = SELECT_DELAY_LONG * 2; | |
251 | } | |
252 | } else if (mybus(reg)) { | |
253 | /* | |
254 | * Bus is on, and we own it. We are done with acquisition. | |
255 | * Reset NTESTON and BUSINIT, then return success. | |
256 | */ | |
257 | if (reg & (PCA9541_CTL_NTESTON | PCA9541_CTL_BUSINIT)) | |
258 | pca9541_reg_write(client, | |
259 | PCA9541_CONTROL, | |
260 | reg & ~(PCA9541_CTL_NTESTON | |
261 | | PCA9541_CTL_BUSINIT)); | |
262 | return 1; | |
263 | } else { | |
264 | /* | |
265 | * Other master owns the bus. | |
266 | * If arbitration timeout has expired, force ownership. | |
267 | * Otherwise request it. | |
268 | */ | |
269 | data->select_timeout = SELECT_DELAY_LONG; | |
270 | if (time_is_before_eq_jiffies(data->arb_timeout)) { | |
271 | /* Time is up, take the bus and reset it. */ | |
272 | pca9541_reg_write(client, | |
273 | PCA9541_CONTROL, | |
274 | pca9541_control[reg & 0x0f] | |
275 | | PCA9541_CTL_BUSINIT | |
276 | | PCA9541_CTL_NTESTON); | |
277 | } else { | |
278 | /* Request bus ownership if needed */ | |
279 | if (!(reg & PCA9541_CTL_NTESTON)) | |
280 | pca9541_reg_write(client, | |
281 | PCA9541_CONTROL, | |
282 | reg | PCA9541_CTL_NTESTON); | |
283 | } | |
284 | } | |
285 | return 0; | |
286 | } | |
287 | ||
288 | static int pca9541_select_chan(struct i2c_adapter *adap, void *client, u32 chan) | |
289 | { | |
290 | struct pca9541 *data = i2c_get_clientdata(client); | |
291 | int ret; | |
292 | unsigned long timeout = jiffies + ARB2_TIMEOUT; | |
293 | /* give up after this time */ | |
294 | ||
295 | data->arb_timeout = jiffies + ARB_TIMEOUT; | |
296 | /* force bus ownership after this time */ | |
297 | ||
298 | do { | |
299 | ret = pca9541_arbitrate(client); | |
300 | if (ret) | |
301 | return ret < 0 ? ret : 0; | |
302 | ||
303 | if (data->select_timeout == SELECT_DELAY_SHORT) | |
304 | udelay(data->select_timeout); | |
305 | else | |
306 | msleep(data->select_timeout / 1000); | |
307 | } while (time_is_after_eq_jiffies(timeout)); | |
308 | ||
309 | return -ETIMEDOUT; | |
310 | } | |
311 | ||
312 | static int pca9541_release_chan(struct i2c_adapter *adap, | |
313 | void *client, u32 chan) | |
314 | { | |
315 | pca9541_release_bus(client); | |
316 | return 0; | |
317 | } | |
318 | ||
319 | /* | |
320 | * I2C init/probing/exit functions | |
321 | */ | |
322 | static int pca9541_probe(struct i2c_client *client, | |
323 | const struct i2c_device_id *id) | |
324 | { | |
325 | struct i2c_adapter *adap = client->adapter; | |
6d4028c6 | 326 | struct pca954x_platform_data *pdata = dev_get_platdata(&client->dev); |
ae63b13b GR |
327 | struct pca9541 *data; |
328 | int force; | |
329 | int ret = -ENODEV; | |
330 | ||
331 | if (!i2c_check_functionality(adap, I2C_FUNC_SMBUS_BYTE_DATA)) | |
332 | goto err; | |
333 | ||
334 | data = kzalloc(sizeof(struct pca9541), GFP_KERNEL); | |
335 | if (!data) { | |
336 | ret = -ENOMEM; | |
337 | goto err; | |
338 | } | |
339 | ||
340 | i2c_set_clientdata(client, data); | |
341 | ||
342 | /* | |
343 | * I2C accesses are unprotected here. | |
344 | * We have to lock the adapter before releasing the bus. | |
345 | */ | |
346 | i2c_lock_adapter(adap); | |
347 | pca9541_release_bus(client); | |
348 | i2c_unlock_adapter(adap); | |
349 | ||
350 | /* Create mux adapter */ | |
351 | ||
352 | force = 0; | |
353 | if (pdata) | |
354 | force = pdata->modes[0].adap_id; | |
5a3ecd5f | 355 | data->mux_adap = i2c_add_mux_adapter(adap, &client->dev, client, |
eee543e8 | 356 | force, 0, 0, |
ae63b13b GR |
357 | pca9541_select_chan, |
358 | pca9541_release_chan); | |
359 | ||
360 | if (data->mux_adap == NULL) { | |
361 | dev_err(&client->dev, "failed to register master selector\n"); | |
362 | goto exit_free; | |
363 | } | |
364 | ||
365 | dev_info(&client->dev, "registered master selector for I2C %s\n", | |
366 | client->name); | |
367 | ||
368 | return 0; | |
369 | ||
370 | exit_free: | |
371 | kfree(data); | |
372 | err: | |
373 | return ret; | |
374 | } | |
375 | ||
376 | static int pca9541_remove(struct i2c_client *client) | |
377 | { | |
378 | struct pca9541 *data = i2c_get_clientdata(client); | |
379 | ||
380 | i2c_del_mux_adapter(data->mux_adap); | |
381 | ||
382 | kfree(data); | |
383 | return 0; | |
384 | } | |
385 | ||
386 | static struct i2c_driver pca9541_driver = { | |
387 | .driver = { | |
388 | .name = "pca9541", | |
389 | .owner = THIS_MODULE, | |
390 | }, | |
391 | .probe = pca9541_probe, | |
392 | .remove = pca9541_remove, | |
393 | .id_table = pca9541_id, | |
394 | }; | |
395 | ||
de05497a | 396 | module_i2c_driver(pca9541_driver); |
ae63b13b | 397 | |
83a638df | 398 | MODULE_AUTHOR("Guenter Roeck <linux@roeck-us.net>"); |
ae63b13b GR |
399 | MODULE_DESCRIPTION("PCA9541 I2C master selector driver"); |
400 | MODULE_LICENSE("GPL v2"); |