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151f4e2b | 1 | ========================================== |
4b875810 NM |
2 | Operating Performance Points (OPP) Library |
3 | ========================================== | |
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4 | |
5 | (C) 2009-2010 Nishanth Menon <nm@ti.com>, Texas Instruments Incorporated | |
6 | ||
151f4e2b MCC |
7 | .. Contents |
8 | ||
9 | 1. Introduction | |
10 | 2. Initial OPP List Registration | |
11 | 3. OPP Search Functions | |
12 | 4. OPP Availability Control Functions | |
13 | 5. OPP Data Retrieval Functions | |
14 | 6. Data Structures | |
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15 | |
16 | 1. Introduction | |
17 | =============== | |
151f4e2b | 18 | |
4b875810 | 19 | 1.1 What is an Operating Performance Point (OPP)? |
151f4e2b | 20 | ------------------------------------------------- |
4b875810 | 21 | |
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22 | Complex SoCs of today consists of a multiple sub-modules working in conjunction. |
23 | In an operational system executing varied use cases, not all modules in the SoC | |
24 | need to function at their highest performing frequency all the time. To | |
25 | facilitate this, sub-modules in a SoC are grouped into domains, allowing some | |
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26 | domains to run at lower voltage and frequency while other domains run at |
27 | voltage/frequency pairs that are higher. | |
28 | ||
29 | The set of discrete tuples consisting of frequency and voltage pairs that | |
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30 | the device will support per domain are called Operating Performance Points or |
31 | OPPs. | |
32 | ||
4b875810 | 33 | As an example: |
151f4e2b | 34 | |
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35 | Let us consider an MPU device which supports the following: |
36 | {300MHz at minimum voltage of 1V}, {800MHz at minimum voltage of 1.2V}, | |
37 | {1GHz at minimum voltage of 1.3V} | |
38 | ||
39 | We can represent these as three OPPs as the following {Hz, uV} tuples: | |
151f4e2b MCC |
40 | |
41 | - {300000000, 1000000} | |
42 | - {800000000, 1200000} | |
43 | - {1000000000, 1300000} | |
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44 | |
45 | 1.2 Operating Performance Points Library | |
151f4e2b | 46 | ---------------------------------------- |
4b875810 | 47 | |
e1f60b29 | 48 | OPP library provides a set of helper functions to organize and query the OPP |
27a84f76 | 49 | information. The library is located in drivers/opp/ directory and the header |
e4db1c74 | 50 | is located in include/linux/pm_opp.h. OPP library can be enabled by enabling |
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51 | CONFIG_PM_OPP from power management menuconfig menu. OPP library depends on |
52 | CONFIG_PM as certain SoCs such as Texas Instrument's OMAP framework allows to | |
53 | optionally boot at a certain OPP without needing cpufreq. | |
54 | ||
151f4e2b MCC |
55 | Typical usage of the OPP library is as follows:: |
56 | ||
57 | (users) -> registers a set of default OPPs -> (library) | |
58 | SoC framework -> modifies on required cases certain OPPs -> OPP layer | |
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59 | -> queries to search/retrieve information -> |
60 | ||
61 | OPP layer expects each domain to be represented by a unique device pointer. SoC | |
62 | framework registers a set of initial OPPs per device with the OPP layer. This | |
63 | list is expected to be an optimally small number typically around 5 per device. | |
64 | This initial list contains a set of OPPs that the framework expects to be safely | |
65 | enabled by default in the system. | |
66 | ||
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67 | Note on OPP Availability |
68 | ^^^^^^^^^^^^^^^^^^^^^^^^ | |
69 | ||
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70 | As the system proceeds to operate, SoC framework may choose to make certain |
71 | OPPs available or not available on each device based on various external | |
72 | factors. Example usage: Thermal management or other exceptional situations where | |
73 | SoC framework might choose to disable a higher frequency OPP to safely continue | |
74 | operations until that OPP could be re-enabled if possible. | |
75 | ||
1992b66d | 76 | OPP library facilitates this concept in its implementation. The following |
e1f60b29 | 77 | operational functions operate only on available opps: |
1992b66d BH |
78 | opp_find_freq_{ceil, floor}, dev_pm_opp_get_voltage, dev_pm_opp_get_freq, |
79 | dev_pm_opp_get_opp_count | |
e1f60b29 | 80 | |
1992b66d BH |
81 | dev_pm_opp_find_freq_exact is meant to be used to find the opp pointer |
82 | which can then be used for dev_pm_opp_enable/disable functions to make an | |
83 | opp available as required. | |
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84 | |
85 | WARNING: Users of OPP library should refresh their availability count using | |
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86 | get_opp_count if dev_pm_opp_enable/disable functions are invoked for a |
87 | device, the exact mechanism to trigger these or the notification mechanism | |
88 | to other dependent subsystems such as cpufreq are left to the discretion of | |
89 | the SoC specific framework which uses the OPP library. Similar care needs | |
90 | to be taken care to refresh the cpufreq table in cases of these operations. | |
e1f60b29 | 91 | |
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92 | 2. Initial OPP List Registration |
93 | ================================ | |
5d4879cd | 94 | The SoC implementation calls dev_pm_opp_add function iteratively to add OPPs per |
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95 | device. It is expected that the SoC framework will register the OPP entries |
96 | optimally- typical numbers range to be less than 5. The list generated by | |
97 | registering the OPPs is maintained by OPP library throughout the device | |
98 | operation. The SoC framework can subsequently control the availability of the | |
5d4879cd | 99 | OPPs dynamically using the dev_pm_opp_enable / disable functions. |
e1f60b29 | 100 | |
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101 | dev_pm_opp_add |
102 | Add a new OPP for a specific domain represented by the device pointer. | |
e1f60b29 | 103 | The OPP is defined using the frequency and voltage. Once added, the OPP |
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104 | is assumed to be available and control of its availability can be done |
105 | with the dev_pm_opp_enable/disable functions. OPP library | |
106 | internally stores and manages this information in the opp struct. | |
107 | This function may be used by SoC framework to define a optimal list | |
108 | as per the demands of SoC usage environment. | |
e1f60b29 | 109 | |
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110 | WARNING: |
111 | Do not use this function in interrupt context. | |
112 | ||
113 | Example:: | |
e1f60b29 | 114 | |
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115 | soc_pm_init() |
116 | { | |
117 | /* Do things */ | |
5d4879cd | 118 | r = dev_pm_opp_add(mpu_dev, 1000000, 900000); |
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119 | if (!r) { |
120 | pr_err("%s: unable to register mpu opp(%d)\n", r); | |
121 | goto no_cpufreq; | |
122 | } | |
123 | /* Do cpufreq things */ | |
124 | no_cpufreq: | |
125 | /* Do remaining things */ | |
126 | } | |
127 | ||
128 | 3. OPP Search Functions | |
129 | ======================= | |
130 | High level framework such as cpufreq operates on frequencies. To map the | |
131 | frequency back to the corresponding OPP, OPP library provides handy functions | |
132 | to search the OPP list that OPP library internally manages. These search | |
133 | functions return the matching pointer representing the opp if a match is | |
134 | found, else returns error. These errors are expected to be handled by standard | |
135 | error checks such as IS_ERR() and appropriate actions taken by the caller. | |
136 | ||
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137 | Callers of these functions shall call dev_pm_opp_put() after they have used the |
138 | OPP. Otherwise the memory for the OPP will never get freed and result in | |
139 | memleak. | |
140 | ||
151f4e2b MCC |
141 | dev_pm_opp_find_freq_exact |
142 | Search for an OPP based on an *exact* frequency and | |
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143 | availability. This function is especially useful to enable an OPP which |
144 | is not available by default. | |
145 | Example: In a case when SoC framework detects a situation where a | |
146 | higher frequency could be made available, it can use this function to | |
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147 | find the OPP prior to call the dev_pm_opp_enable to actually make |
148 | it available:: | |
149 | ||
5d4879cd | 150 | opp = dev_pm_opp_find_freq_exact(dev, 1000000000, false); |
6185deaa | 151 | dev_pm_opp_put(opp); |
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152 | /* dont operate on the pointer.. just do a sanity check.. */ |
153 | if (IS_ERR(opp)) { | |
154 | pr_err("frequency not disabled!\n"); | |
155 | /* trigger appropriate actions.. */ | |
156 | } else { | |
5d4879cd | 157 | dev_pm_opp_enable(dev,1000000000); |
e1f60b29 NM |
158 | } |
159 | ||
151f4e2b MCC |
160 | NOTE: |
161 | This is the only search function that operates on OPPs which are | |
162 | not available. | |
e1f60b29 | 163 | |
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164 | dev_pm_opp_find_freq_floor |
165 | Search for an available OPP which is *at most* the | |
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166 | provided frequency. This function is useful while searching for a lesser |
167 | match OR operating on OPP information in the order of decreasing | |
168 | frequency. | |
151f4e2b MCC |
169 | Example: To find the highest opp for a device:: |
170 | ||
e1f60b29 | 171 | freq = ULONG_MAX; |
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172 | opp = dev_pm_opp_find_freq_floor(dev, &freq); |
173 | dev_pm_opp_put(opp); | |
e1f60b29 | 174 | |
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175 | dev_pm_opp_find_freq_ceil |
176 | Search for an available OPP which is *at least* the | |
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177 | provided frequency. This function is useful while searching for a |
178 | higher match OR operating on OPP information in the order of increasing | |
179 | frequency. | |
151f4e2b MCC |
180 | Example 1: To find the lowest opp for a device:: |
181 | ||
e1f60b29 | 182 | freq = 0; |
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183 | opp = dev_pm_opp_find_freq_ceil(dev, &freq); |
184 | dev_pm_opp_put(opp); | |
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185 | |
186 | Example 2: A simplified implementation of a SoC cpufreq_driver->target:: | |
187 | ||
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188 | soc_cpufreq_target(..) |
189 | { | |
190 | /* Do stuff like policy checks etc. */ | |
191 | /* Find the best frequency match for the req */ | |
5d4879cd | 192 | opp = dev_pm_opp_find_freq_ceil(dev, &freq); |
6185deaa | 193 | dev_pm_opp_put(opp); |
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194 | if (!IS_ERR(opp)) |
195 | soc_switch_to_freq_voltage(freq); | |
196 | else | |
25985edc | 197 | /* do something when we can't satisfy the req */ |
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198 | /* do other stuff */ |
199 | } | |
200 | ||
201 | 4. OPP Availability Control Functions | |
202 | ===================================== | |
203 | A default OPP list registered with the OPP library may not cater to all possible | |
204 | situation. The OPP library provides a set of functions to modify the | |
205 | availability of a OPP within the OPP list. This allows SoC frameworks to have | |
206 | fine grained dynamic control of which sets of OPPs are operationally available. | |
207 | These functions are intended to *temporarily* remove an OPP in conditions such | |
208 | as thermal considerations (e.g. don't use OPPx until the temperature drops). | |
209 | ||
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210 | WARNING: |
211 | Do not use these functions in interrupt context. | |
e1f60b29 | 212 | |
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213 | dev_pm_opp_enable |
214 | Make a OPP available for operation. | |
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215 | Example: Lets say that 1GHz OPP is to be made available only if the |
216 | SoC temperature is lower than a certain threshold. The SoC framework | |
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217 | implementation might choose to do something as follows:: |
218 | ||
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219 | if (cur_temp < temp_low_thresh) { |
220 | /* Enable 1GHz if it was disabled */ | |
5d4879cd | 221 | opp = dev_pm_opp_find_freq_exact(dev, 1000000000, false); |
6185deaa | 222 | dev_pm_opp_put(opp); |
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223 | /* just error check */ |
224 | if (!IS_ERR(opp)) | |
5d4879cd | 225 | ret = dev_pm_opp_enable(dev, 1000000000); |
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226 | else |
227 | goto try_something_else; | |
228 | } | |
229 | ||
151f4e2b MCC |
230 | dev_pm_opp_disable |
231 | Make an OPP to be not available for operation | |
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232 | Example: Lets say that 1GHz OPP is to be disabled if the temperature |
233 | exceeds a threshold value. The SoC framework implementation might | |
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234 | choose to do something as follows:: |
235 | ||
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236 | if (cur_temp > temp_high_thresh) { |
237 | /* Disable 1GHz if it was enabled */ | |
5d4879cd | 238 | opp = dev_pm_opp_find_freq_exact(dev, 1000000000, true); |
6185deaa | 239 | dev_pm_opp_put(opp); |
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240 | /* just error check */ |
241 | if (!IS_ERR(opp)) | |
5d4879cd | 242 | ret = dev_pm_opp_disable(dev, 1000000000); |
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243 | else |
244 | goto try_something_else; | |
245 | } | |
246 | ||
247 | 5. OPP Data Retrieval Functions | |
248 | =============================== | |
249 | Since OPP library abstracts away the OPP information, a set of functions to pull | |
250 | information from the OPP structure is necessary. Once an OPP pointer is | |
251 | retrieved using the search functions, the following functions can be used by SoC | |
252 | framework to retrieve the information represented inside the OPP layer. | |
253 | ||
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254 | dev_pm_opp_get_voltage |
255 | Retrieve the voltage represented by the opp pointer. | |
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256 | Example: At a cpufreq transition to a different frequency, SoC |
257 | framework requires to set the voltage represented by the OPP using | |
258 | the regulator framework to the Power Management chip providing the | |
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259 | voltage:: |
260 | ||
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261 | soc_switch_to_freq_voltage(freq) |
262 | { | |
263 | /* do things */ | |
5d4879cd NM |
264 | opp = dev_pm_opp_find_freq_ceil(dev, &freq); |
265 | v = dev_pm_opp_get_voltage(opp); | |
6185deaa | 266 | dev_pm_opp_put(opp); |
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267 | if (v) |
268 | regulator_set_voltage(.., v); | |
269 | /* do other things */ | |
270 | } | |
271 | ||
151f4e2b MCC |
272 | dev_pm_opp_get_freq |
273 | Retrieve the freq represented by the opp pointer. | |
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274 | Example: Lets say the SoC framework uses a couple of helper functions |
275 | we could pass opp pointers instead of doing additional parameters to | |
151f4e2b MCC |
276 | handle quiet a bit of data parameters:: |
277 | ||
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278 | soc_cpufreq_target(..) |
279 | { | |
280 | /* do things.. */ | |
281 | max_freq = ULONG_MAX; | |
5d4879cd NM |
282 | max_opp = dev_pm_opp_find_freq_floor(dev,&max_freq); |
283 | requested_opp = dev_pm_opp_find_freq_ceil(dev,&freq); | |
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284 | if (!IS_ERR(max_opp) && !IS_ERR(requested_opp)) |
285 | r = soc_test_validity(max_opp, requested_opp); | |
6185deaa VK |
286 | dev_pm_opp_put(max_opp); |
287 | dev_pm_opp_put(requested_opp); | |
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288 | /* do other things */ |
289 | } | |
290 | soc_test_validity(..) | |
291 | { | |
5d4879cd | 292 | if(dev_pm_opp_get_voltage(max_opp) < dev_pm_opp_get_voltage(requested_opp)) |
e1f60b29 | 293 | return -EINVAL; |
5d4879cd | 294 | if(dev_pm_opp_get_freq(max_opp) < dev_pm_opp_get_freq(requested_opp)) |
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295 | return -EINVAL; |
296 | /* do things.. */ | |
297 | } | |
298 | ||
151f4e2b MCC |
299 | dev_pm_opp_get_opp_count |
300 | Retrieve the number of available opps for a device | |
e1f60b29 | 301 | Example: Lets say a co-processor in the SoC needs to know the available |
151f4e2b MCC |
302 | frequencies in a table, the main processor can notify as following:: |
303 | ||
e1f60b29 NM |
304 | soc_notify_coproc_available_frequencies() |
305 | { | |
306 | /* Do things */ | |
5d4879cd | 307 | num_available = dev_pm_opp_get_opp_count(dev); |
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308 | speeds = kzalloc(sizeof(u32) * num_available, GFP_KERNEL); |
309 | /* populate the table in increasing order */ | |
310 | freq = 0; | |
5d4879cd | 311 | while (!IS_ERR(opp = dev_pm_opp_find_freq_ceil(dev, &freq))) { |
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312 | speeds[i] = freq; |
313 | freq++; | |
314 | i++; | |
6185deaa | 315 | dev_pm_opp_put(opp); |
e1f60b29 | 316 | } |
e1f60b29 NM |
317 | |
318 | soc_notify_coproc(AVAILABLE_FREQs, speeds, num_available); | |
319 | /* Do other things */ | |
320 | } | |
321 | ||
a0dd7b79 | 322 | 6. Data Structures |
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323 | ================== |
324 | Typically an SoC contains multiple voltage domains which are variable. Each | |
325 | domain is represented by a device pointer. The relationship to OPP can be | |
151f4e2b MCC |
326 | represented as follows:: |
327 | ||
328 | SoC | |
329 | |- device 1 | |
330 | | |- opp 1 (availability, freq, voltage) | |
331 | | |- opp 2 .. | |
332 | ... ... | |
333 | | `- opp n .. | |
334 | |- device 2 | |
335 | ... | |
336 | `- device m | |
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337 | |
338 | OPP library maintains a internal list that the SoC framework populates and | |
339 | accessed by various functions as described above. However, the structures | |
340 | representing the actual OPPs and domains are internal to the OPP library itself | |
341 | to allow for suitable abstraction reusable across systems. | |
342 | ||
151f4e2b MCC |
343 | struct dev_pm_opp |
344 | The internal data structure of OPP library which is used to | |
e1f60b29 NM |
345 | represent an OPP. In addition to the freq, voltage, availability |
346 | information, it also contains internal book keeping information required | |
347 | for the OPP library to operate on. Pointer to this structure is | |
348 | provided back to the users such as SoC framework to be used as a | |
349 | identifier for OPP in the interactions with OPP layer. | |
350 | ||
151f4e2b MCC |
351 | WARNING: |
352 | The struct dev_pm_opp pointer should not be parsed or modified by the | |
353 | users. The defaults of for an instance is populated by | |
354 | dev_pm_opp_add, but the availability of the OPP can be modified | |
355 | by dev_pm_opp_enable/disable functions. | |
e1f60b29 | 356 | |
151f4e2b MCC |
357 | struct device |
358 | This is used to identify a domain to the OPP layer. The | |
1992b66d | 359 | nature of the device and its implementation is left to the user of |
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360 | OPP library such as the SoC framework. |
361 | ||
362 | Overall, in a simplistic view, the data structure operations is represented as | |
151f4e2b | 363 | following:: |
e1f60b29 | 364 | |
151f4e2b MCC |
365 | Initialization / modification: |
366 | +-----+ /- dev_pm_opp_enable | |
367 | dev_pm_opp_add --> | opp | <------- | |
368 | | +-----+ \- dev_pm_opp_disable | |
369 | \-------> domain_info(device) | |
e1f60b29 | 370 | |
151f4e2b MCC |
371 | Search functions: |
372 | /-- dev_pm_opp_find_freq_ceil ---\ +-----+ | |
373 | domain_info<---- dev_pm_opp_find_freq_exact -----> | opp | | |
374 | \-- dev_pm_opp_find_freq_floor ---/ +-----+ | |
e1f60b29 | 375 | |
151f4e2b MCC |
376 | Retrieval functions: |
377 | +-----+ /- dev_pm_opp_get_voltage | |
378 | | opp | <--- | |
379 | +-----+ \- dev_pm_opp_get_freq | |
e1f60b29 | 380 | |
151f4e2b | 381 | domain_info <- dev_pm_opp_get_opp_count |