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1 | Operating Performance Points (OPP) Library |
2 | ========================================== | |
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3 | |
4 | (C) 2009-2010 Nishanth Menon <nm@ti.com>, Texas Instruments Incorporated | |
5 | ||
6 | Contents | |
7 | -------- | |
8 | 1. Introduction | |
9 | 2. Initial OPP List Registration | |
10 | 3. OPP Search Functions | |
11 | 4. OPP Availability Control Functions | |
12 | 5. OPP Data Retrieval Functions | |
a0dd7b79 | 13 | 6. Data Structures |
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14 | |
15 | 1. Introduction | |
16 | =============== | |
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17 | 1.1 What is an Operating Performance Point (OPP)? |
18 | ||
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19 | Complex SoCs of today consists of a multiple sub-modules working in conjunction. |
20 | In an operational system executing varied use cases, not all modules in the SoC | |
21 | need to function at their highest performing frequency all the time. To | |
22 | facilitate this, sub-modules in a SoC are grouped into domains, allowing some | |
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23 | domains to run at lower voltage and frequency while other domains run at |
24 | voltage/frequency pairs that are higher. | |
25 | ||
26 | The set of discrete tuples consisting of frequency and voltage pairs that | |
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27 | the device will support per domain are called Operating Performance Points or |
28 | OPPs. | |
29 | ||
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30 | As an example: |
31 | Let us consider an MPU device which supports the following: | |
32 | {300MHz at minimum voltage of 1V}, {800MHz at minimum voltage of 1.2V}, | |
33 | {1GHz at minimum voltage of 1.3V} | |
34 | ||
35 | We can represent these as three OPPs as the following {Hz, uV} tuples: | |
36 | {300000000, 1000000} | |
37 | {800000000, 1200000} | |
38 | {1000000000, 1300000} | |
39 | ||
40 | 1.2 Operating Performance Points Library | |
41 | ||
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42 | OPP library provides a set of helper functions to organize and query the OPP |
43 | information. The library is located in drivers/base/power/opp.c and the header | |
e4db1c74 | 44 | is located in include/linux/pm_opp.h. OPP library can be enabled by enabling |
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45 | CONFIG_PM_OPP from power management menuconfig menu. OPP library depends on |
46 | CONFIG_PM as certain SoCs such as Texas Instrument's OMAP framework allows to | |
47 | optionally boot at a certain OPP without needing cpufreq. | |
48 | ||
49 | Typical usage of the OPP library is as follows: | |
50 | (users) -> registers a set of default OPPs -> (library) | |
51 | SoC framework -> modifies on required cases certain OPPs -> OPP layer | |
52 | -> queries to search/retrieve information -> | |
53 | ||
54 | OPP layer expects each domain to be represented by a unique device pointer. SoC | |
55 | framework registers a set of initial OPPs per device with the OPP layer. This | |
56 | list is expected to be an optimally small number typically around 5 per device. | |
57 | This initial list contains a set of OPPs that the framework expects to be safely | |
58 | enabled by default in the system. | |
59 | ||
60 | Note on OPP Availability: | |
61 | ------------------------ | |
62 | As the system proceeds to operate, SoC framework may choose to make certain | |
63 | OPPs available or not available on each device based on various external | |
64 | factors. Example usage: Thermal management or other exceptional situations where | |
65 | SoC framework might choose to disable a higher frequency OPP to safely continue | |
66 | operations until that OPP could be re-enabled if possible. | |
67 | ||
68 | OPP library facilitates this concept in it's implementation. The following | |
69 | operational functions operate only on available opps: | |
5d4879cd | 70 | opp_find_freq_{ceil, floor}, dev_pm_opp_get_voltage, dev_pm_opp_get_freq, dev_pm_opp_get_opp_count |
e1f60b29 | 71 | |
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72 | dev_pm_opp_find_freq_exact is meant to be used to find the opp pointer which can then |
73 | be used for dev_pm_opp_enable/disable functions to make an opp available as required. | |
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74 | |
75 | WARNING: Users of OPP library should refresh their availability count using | |
5d4879cd | 76 | get_opp_count if dev_pm_opp_enable/disable functions are invoked for a device, the |
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77 | exact mechanism to trigger these or the notification mechanism to other |
78 | dependent subsystems such as cpufreq are left to the discretion of the SoC | |
79 | specific framework which uses the OPP library. Similar care needs to be taken | |
80 | care to refresh the cpufreq table in cases of these operations. | |
81 | ||
82 | WARNING on OPP List locking mechanism: | |
83 | ------------------------------------------------- | |
84 | OPP library uses RCU for exclusivity. RCU allows the query functions to operate | |
85 | in multiple contexts and this synchronization mechanism is optimal for a read | |
86 | intensive operations on data structure as the OPP library caters to. | |
87 | ||
88 | To ensure that the data retrieved are sane, the users such as SoC framework | |
89 | should ensure that the section of code operating on OPP queries are locked | |
90 | using RCU read locks. The opp_find_freq_{exact,ceil,floor}, | |
91 | opp_get_{voltage, freq, opp_count} fall into this category. | |
92 | ||
93 | opp_{add,enable,disable} are updaters which use mutex and implement it's own | |
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94 | RCU locking mechanisms. These functions should *NOT* be called under RCU locks |
95 | and other contexts that prevent blocking functions in RCU or mutex operations | |
96 | from working. | |
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97 | |
98 | 2. Initial OPP List Registration | |
99 | ================================ | |
5d4879cd | 100 | The SoC implementation calls dev_pm_opp_add function iteratively to add OPPs per |
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101 | device. It is expected that the SoC framework will register the OPP entries |
102 | optimally- typical numbers range to be less than 5. The list generated by | |
103 | registering the OPPs is maintained by OPP library throughout the device | |
104 | operation. The SoC framework can subsequently control the availability of the | |
5d4879cd | 105 | OPPs dynamically using the dev_pm_opp_enable / disable functions. |
e1f60b29 | 106 | |
5d4879cd | 107 | dev_pm_opp_add - Add a new OPP for a specific domain represented by the device pointer. |
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108 | The OPP is defined using the frequency and voltage. Once added, the OPP |
109 | is assumed to be available and control of it's availability can be done | |
5d4879cd | 110 | with the dev_pm_opp_enable/disable functions. OPP library internally stores |
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111 | and manages this information in the opp struct. This function may be |
112 | used by SoC framework to define a optimal list as per the demands of | |
113 | SoC usage environment. | |
114 | ||
115 | WARNING: Do not use this function in interrupt context. | |
116 | ||
117 | Example: | |
118 | soc_pm_init() | |
119 | { | |
120 | /* Do things */ | |
5d4879cd | 121 | r = dev_pm_opp_add(mpu_dev, 1000000, 900000); |
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122 | if (!r) { |
123 | pr_err("%s: unable to register mpu opp(%d)\n", r); | |
124 | goto no_cpufreq; | |
125 | } | |
126 | /* Do cpufreq things */ | |
127 | no_cpufreq: | |
128 | /* Do remaining things */ | |
129 | } | |
130 | ||
131 | 3. OPP Search Functions | |
132 | ======================= | |
133 | High level framework such as cpufreq operates on frequencies. To map the | |
134 | frequency back to the corresponding OPP, OPP library provides handy functions | |
135 | to search the OPP list that OPP library internally manages. These search | |
136 | functions return the matching pointer representing the opp if a match is | |
137 | found, else returns error. These errors are expected to be handled by standard | |
138 | error checks such as IS_ERR() and appropriate actions taken by the caller. | |
139 | ||
5d4879cd | 140 | dev_pm_opp_find_freq_exact - Search for an OPP based on an *exact* frequency and |
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141 | availability. This function is especially useful to enable an OPP which |
142 | is not available by default. | |
143 | Example: In a case when SoC framework detects a situation where a | |
144 | higher frequency could be made available, it can use this function to | |
5d4879cd | 145 | find the OPP prior to call the dev_pm_opp_enable to actually make it available. |
e1f60b29 | 146 | rcu_read_lock(); |
5d4879cd | 147 | opp = dev_pm_opp_find_freq_exact(dev, 1000000000, false); |
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148 | rcu_read_unlock(); |
149 | /* dont operate on the pointer.. just do a sanity check.. */ | |
150 | if (IS_ERR(opp)) { | |
151 | pr_err("frequency not disabled!\n"); | |
152 | /* trigger appropriate actions.. */ | |
153 | } else { | |
5d4879cd | 154 | dev_pm_opp_enable(dev,1000000000); |
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155 | } |
156 | ||
157 | NOTE: This is the only search function that operates on OPPs which are | |
158 | not available. | |
159 | ||
5d4879cd | 160 | dev_pm_opp_find_freq_floor - Search for an available OPP which is *at most* the |
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161 | provided frequency. This function is useful while searching for a lesser |
162 | match OR operating on OPP information in the order of decreasing | |
163 | frequency. | |
164 | Example: To find the highest opp for a device: | |
165 | freq = ULONG_MAX; | |
166 | rcu_read_lock(); | |
5d4879cd | 167 | dev_pm_opp_find_freq_floor(dev, &freq); |
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168 | rcu_read_unlock(); |
169 | ||
5d4879cd | 170 | dev_pm_opp_find_freq_ceil - Search for an available OPP which is *at least* the |
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171 | provided frequency. This function is useful while searching for a |
172 | higher match OR operating on OPP information in the order of increasing | |
173 | frequency. | |
174 | Example 1: To find the lowest opp for a device: | |
175 | freq = 0; | |
176 | rcu_read_lock(); | |
5d4879cd | 177 | dev_pm_opp_find_freq_ceil(dev, &freq); |
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178 | rcu_read_unlock(); |
179 | Example 2: A simplified implementation of a SoC cpufreq_driver->target: | |
180 | soc_cpufreq_target(..) | |
181 | { | |
182 | /* Do stuff like policy checks etc. */ | |
183 | /* Find the best frequency match for the req */ | |
184 | rcu_read_lock(); | |
5d4879cd | 185 | opp = dev_pm_opp_find_freq_ceil(dev, &freq); |
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186 | rcu_read_unlock(); |
187 | if (!IS_ERR(opp)) | |
188 | soc_switch_to_freq_voltage(freq); | |
189 | else | |
25985edc | 190 | /* do something when we can't satisfy the req */ |
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191 | /* do other stuff */ |
192 | } | |
193 | ||
194 | 4. OPP Availability Control Functions | |
195 | ===================================== | |
196 | A default OPP list registered with the OPP library may not cater to all possible | |
197 | situation. The OPP library provides a set of functions to modify the | |
198 | availability of a OPP within the OPP list. This allows SoC frameworks to have | |
199 | fine grained dynamic control of which sets of OPPs are operationally available. | |
200 | These functions are intended to *temporarily* remove an OPP in conditions such | |
201 | as thermal considerations (e.g. don't use OPPx until the temperature drops). | |
202 | ||
203 | WARNING: Do not use these functions in interrupt context. | |
204 | ||
5d4879cd | 205 | dev_pm_opp_enable - Make a OPP available for operation. |
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206 | Example: Lets say that 1GHz OPP is to be made available only if the |
207 | SoC temperature is lower than a certain threshold. The SoC framework | |
208 | implementation might choose to do something as follows: | |
209 | if (cur_temp < temp_low_thresh) { | |
210 | /* Enable 1GHz if it was disabled */ | |
211 | rcu_read_lock(); | |
5d4879cd | 212 | opp = dev_pm_opp_find_freq_exact(dev, 1000000000, false); |
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213 | rcu_read_unlock(); |
214 | /* just error check */ | |
215 | if (!IS_ERR(opp)) | |
5d4879cd | 216 | ret = dev_pm_opp_enable(dev, 1000000000); |
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217 | else |
218 | goto try_something_else; | |
219 | } | |
220 | ||
5d4879cd | 221 | dev_pm_opp_disable - Make an OPP to be not available for operation |
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222 | Example: Lets say that 1GHz OPP is to be disabled if the temperature |
223 | exceeds a threshold value. The SoC framework implementation might | |
224 | choose to do something as follows: | |
225 | if (cur_temp > temp_high_thresh) { | |
226 | /* Disable 1GHz if it was enabled */ | |
227 | rcu_read_lock(); | |
5d4879cd | 228 | opp = dev_pm_opp_find_freq_exact(dev, 1000000000, true); |
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229 | rcu_read_unlock(); |
230 | /* just error check */ | |
231 | if (!IS_ERR(opp)) | |
5d4879cd | 232 | ret = dev_pm_opp_disable(dev, 1000000000); |
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233 | else |
234 | goto try_something_else; | |
235 | } | |
236 | ||
237 | 5. OPP Data Retrieval Functions | |
238 | =============================== | |
239 | Since OPP library abstracts away the OPP information, a set of functions to pull | |
240 | information from the OPP structure is necessary. Once an OPP pointer is | |
241 | retrieved using the search functions, the following functions can be used by SoC | |
242 | framework to retrieve the information represented inside the OPP layer. | |
243 | ||
5d4879cd | 244 | dev_pm_opp_get_voltage - Retrieve the voltage represented by the opp pointer. |
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245 | Example: At a cpufreq transition to a different frequency, SoC |
246 | framework requires to set the voltage represented by the OPP using | |
247 | the regulator framework to the Power Management chip providing the | |
248 | voltage. | |
249 | soc_switch_to_freq_voltage(freq) | |
250 | { | |
251 | /* do things */ | |
252 | rcu_read_lock(); | |
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253 | opp = dev_pm_opp_find_freq_ceil(dev, &freq); |
254 | v = dev_pm_opp_get_voltage(opp); | |
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255 | rcu_read_unlock(); |
256 | if (v) | |
257 | regulator_set_voltage(.., v); | |
258 | /* do other things */ | |
259 | } | |
260 | ||
5d4879cd | 261 | dev_pm_opp_get_freq - Retrieve the freq represented by the opp pointer. |
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262 | Example: Lets say the SoC framework uses a couple of helper functions |
263 | we could pass opp pointers instead of doing additional parameters to | |
264 | handle quiet a bit of data parameters. | |
265 | soc_cpufreq_target(..) | |
266 | { | |
267 | /* do things.. */ | |
268 | max_freq = ULONG_MAX; | |
269 | rcu_read_lock(); | |
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270 | max_opp = dev_pm_opp_find_freq_floor(dev,&max_freq); |
271 | requested_opp = dev_pm_opp_find_freq_ceil(dev,&freq); | |
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272 | if (!IS_ERR(max_opp) && !IS_ERR(requested_opp)) |
273 | r = soc_test_validity(max_opp, requested_opp); | |
274 | rcu_read_unlock(); | |
275 | /* do other things */ | |
276 | } | |
277 | soc_test_validity(..) | |
278 | { | |
5d4879cd | 279 | if(dev_pm_opp_get_voltage(max_opp) < dev_pm_opp_get_voltage(requested_opp)) |
e1f60b29 | 280 | return -EINVAL; |
5d4879cd | 281 | if(dev_pm_opp_get_freq(max_opp) < dev_pm_opp_get_freq(requested_opp)) |
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282 | return -EINVAL; |
283 | /* do things.. */ | |
284 | } | |
285 | ||
5d4879cd | 286 | dev_pm_opp_get_opp_count - Retrieve the number of available opps for a device |
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287 | Example: Lets say a co-processor in the SoC needs to know the available |
288 | frequencies in a table, the main processor can notify as following: | |
289 | soc_notify_coproc_available_frequencies() | |
290 | { | |
291 | /* Do things */ | |
292 | rcu_read_lock(); | |
5d4879cd | 293 | num_available = dev_pm_opp_get_opp_count(dev); |
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294 | speeds = kzalloc(sizeof(u32) * num_available, GFP_KERNEL); |
295 | /* populate the table in increasing order */ | |
296 | freq = 0; | |
5d4879cd | 297 | while (!IS_ERR(opp = dev_pm_opp_find_freq_ceil(dev, &freq))) { |
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298 | speeds[i] = freq; |
299 | freq++; | |
300 | i++; | |
301 | } | |
302 | rcu_read_unlock(); | |
303 | ||
304 | soc_notify_coproc(AVAILABLE_FREQs, speeds, num_available); | |
305 | /* Do other things */ | |
306 | } | |
307 | ||
a0dd7b79 | 308 | 6. Data Structures |
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309 | ================== |
310 | Typically an SoC contains multiple voltage domains which are variable. Each | |
311 | domain is represented by a device pointer. The relationship to OPP can be | |
312 | represented as follows: | |
313 | SoC | |
314 | |- device 1 | |
315 | | |- opp 1 (availability, freq, voltage) | |
316 | | |- opp 2 .. | |
317 | ... ... | |
318 | | `- opp n .. | |
319 | |- device 2 | |
320 | ... | |
321 | `- device m | |
322 | ||
323 | OPP library maintains a internal list that the SoC framework populates and | |
324 | accessed by various functions as described above. However, the structures | |
325 | representing the actual OPPs and domains are internal to the OPP library itself | |
326 | to allow for suitable abstraction reusable across systems. | |
327 | ||
47d43ba7 | 328 | struct dev_pm_opp - The internal data structure of OPP library which is used to |
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329 | represent an OPP. In addition to the freq, voltage, availability |
330 | information, it also contains internal book keeping information required | |
331 | for the OPP library to operate on. Pointer to this structure is | |
332 | provided back to the users such as SoC framework to be used as a | |
333 | identifier for OPP in the interactions with OPP layer. | |
334 | ||
47d43ba7 | 335 | WARNING: The struct dev_pm_opp pointer should not be parsed or modified by the |
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336 | users. The defaults of for an instance is populated by dev_pm_opp_add, but the |
337 | availability of the OPP can be modified by dev_pm_opp_enable/disable functions. | |
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338 | |
339 | struct device - This is used to identify a domain to the OPP layer. The | |
340 | nature of the device and it's implementation is left to the user of | |
341 | OPP library such as the SoC framework. | |
342 | ||
343 | Overall, in a simplistic view, the data structure operations is represented as | |
344 | following: | |
345 | ||
346 | Initialization / modification: | |
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347 | +-----+ /- dev_pm_opp_enable |
348 | dev_pm_opp_add --> | opp | <------- | |
349 | | +-----+ \- dev_pm_opp_disable | |
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350 | \-------> domain_info(device) |
351 | ||
352 | Search functions: | |
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353 | /-- dev_pm_opp_find_freq_ceil ---\ +-----+ |
354 | domain_info<---- dev_pm_opp_find_freq_exact -----> | opp | | |
355 | \-- dev_pm_opp_find_freq_floor ---/ +-----+ | |
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356 | |
357 | Retrieval functions: | |
5d4879cd | 358 | +-----+ /- dev_pm_opp_get_voltage |
e1f60b29 | 359 | | opp | <--- |
5d4879cd | 360 | +-----+ \- dev_pm_opp_get_freq |
e1f60b29 | 361 | |
5d4879cd | 362 | domain_info <- dev_pm_opp_get_opp_count |