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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 | |
13 | 6. Cpufreq Table Generation | |
14 | 7. Data Structures | |
15 | ||
16 | 1. Introduction | |
17 | =============== | |
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18 | 1.1 What is an Operating Performance Point (OPP)? |
19 | ||
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20 | Complex SoCs of today consists of a multiple sub-modules working in conjunction. |
21 | In an operational system executing varied use cases, not all modules in the SoC | |
22 | need to function at their highest performing frequency all the time. To | |
23 | facilitate this, sub-modules in a SoC are grouped into domains, allowing some | |
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24 | domains to run at lower voltage and frequency while other domains run at |
25 | voltage/frequency pairs that are higher. | |
26 | ||
27 | The set of discrete tuples consisting of frequency and voltage pairs that | |
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28 | the device will support per domain are called Operating Performance Points or |
29 | OPPs. | |
30 | ||
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31 | As an example: |
32 | Let us consider an MPU device which supports the following: | |
33 | {300MHz at minimum voltage of 1V}, {800MHz at minimum voltage of 1.2V}, | |
34 | {1GHz at minimum voltage of 1.3V} | |
35 | ||
36 | We can represent these as three OPPs as the following {Hz, uV} tuples: | |
37 | {300000000, 1000000} | |
38 | {800000000, 1200000} | |
39 | {1000000000, 1300000} | |
40 | ||
41 | 1.2 Operating Performance Points Library | |
42 | ||
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43 | OPP library provides a set of helper functions to organize and query the OPP |
44 | information. The library is located in drivers/base/power/opp.c and the header | |
45 | is located in include/linux/opp.h. OPP library can be enabled by enabling | |
46 | CONFIG_PM_OPP from power management menuconfig menu. OPP library depends on | |
47 | CONFIG_PM as certain SoCs such as Texas Instrument's OMAP framework allows to | |
48 | optionally boot at a certain OPP without needing cpufreq. | |
49 | ||
50 | Typical usage of the OPP library is as follows: | |
51 | (users) -> registers a set of default OPPs -> (library) | |
52 | SoC framework -> modifies on required cases certain OPPs -> OPP layer | |
53 | -> queries to search/retrieve information -> | |
54 | ||
43e60861 MB |
55 | Architectures that provide a SoC framework for OPP should select ARCH_HAS_OPP |
56 | to make the OPP layer available. | |
57 | ||
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58 | OPP layer expects each domain to be represented by a unique device pointer. SoC |
59 | framework registers a set of initial OPPs per device with the OPP layer. This | |
60 | list is expected to be an optimally small number typically around 5 per device. | |
61 | This initial list contains a set of OPPs that the framework expects to be safely | |
62 | enabled by default in the system. | |
63 | ||
64 | Note on OPP Availability: | |
65 | ------------------------ | |
66 | As the system proceeds to operate, SoC framework may choose to make certain | |
67 | OPPs available or not available on each device based on various external | |
68 | factors. Example usage: Thermal management or other exceptional situations where | |
69 | SoC framework might choose to disable a higher frequency OPP to safely continue | |
70 | operations until that OPP could be re-enabled if possible. | |
71 | ||
72 | OPP library facilitates this concept in it's implementation. The following | |
73 | operational functions operate only on available opps: | |
74 | opp_find_freq_{ceil, floor}, opp_get_voltage, opp_get_freq, opp_get_opp_count | |
75 | and opp_init_cpufreq_table | |
76 | ||
77 | opp_find_freq_exact is meant to be used to find the opp pointer which can then | |
78 | be used for opp_enable/disable functions to make an opp available as required. | |
79 | ||
80 | WARNING: Users of OPP library should refresh their availability count using | |
81 | get_opp_count if opp_enable/disable functions are invoked for a device, the | |
82 | exact mechanism to trigger these or the notification mechanism to other | |
83 | dependent subsystems such as cpufreq are left to the discretion of the SoC | |
84 | specific framework which uses the OPP library. Similar care needs to be taken | |
85 | care to refresh the cpufreq table in cases of these operations. | |
86 | ||
87 | WARNING on OPP List locking mechanism: | |
88 | ------------------------------------------------- | |
89 | OPP library uses RCU for exclusivity. RCU allows the query functions to operate | |
90 | in multiple contexts and this synchronization mechanism is optimal for a read | |
91 | intensive operations on data structure as the OPP library caters to. | |
92 | ||
93 | To ensure that the data retrieved are sane, the users such as SoC framework | |
94 | should ensure that the section of code operating on OPP queries are locked | |
95 | using RCU read locks. The opp_find_freq_{exact,ceil,floor}, | |
96 | opp_get_{voltage, freq, opp_count} fall into this category. | |
97 | ||
98 | opp_{add,enable,disable} are updaters which use mutex and implement it's own | |
99 | RCU locking mechanisms. opp_init_cpufreq_table acts as an updater and uses | |
100 | mutex to implment RCU updater strategy. These functions should *NOT* be called | |
101 | under RCU locks and other contexts that prevent blocking functions in RCU or | |
102 | mutex operations from working. | |
103 | ||
104 | 2. Initial OPP List Registration | |
105 | ================================ | |
106 | The SoC implementation calls opp_add function iteratively to add OPPs per | |
107 | device. It is expected that the SoC framework will register the OPP entries | |
108 | optimally- typical numbers range to be less than 5. The list generated by | |
109 | registering the OPPs is maintained by OPP library throughout the device | |
110 | operation. The SoC framework can subsequently control the availability of the | |
111 | OPPs dynamically using the opp_enable / disable functions. | |
112 | ||
113 | opp_add - Add a new OPP for a specific domain represented by the device pointer. | |
114 | The OPP is defined using the frequency and voltage. Once added, the OPP | |
115 | is assumed to be available and control of it's availability can be done | |
116 | with the opp_enable/disable functions. OPP library internally stores | |
117 | and manages this information in the opp struct. This function may be | |
118 | used by SoC framework to define a optimal list as per the demands of | |
119 | SoC usage environment. | |
120 | ||
121 | WARNING: Do not use this function in interrupt context. | |
122 | ||
123 | Example: | |
124 | soc_pm_init() | |
125 | { | |
126 | /* Do things */ | |
127 | r = opp_add(mpu_dev, 1000000, 900000); | |
128 | if (!r) { | |
129 | pr_err("%s: unable to register mpu opp(%d)\n", r); | |
130 | goto no_cpufreq; | |
131 | } | |
132 | /* Do cpufreq things */ | |
133 | no_cpufreq: | |
134 | /* Do remaining things */ | |
135 | } | |
136 | ||
137 | 3. OPP Search Functions | |
138 | ======================= | |
139 | High level framework such as cpufreq operates on frequencies. To map the | |
140 | frequency back to the corresponding OPP, OPP library provides handy functions | |
141 | to search the OPP list that OPP library internally manages. These search | |
142 | functions return the matching pointer representing the opp if a match is | |
143 | found, else returns error. These errors are expected to be handled by standard | |
144 | error checks such as IS_ERR() and appropriate actions taken by the caller. | |
145 | ||
146 | opp_find_freq_exact - Search for an OPP based on an *exact* frequency and | |
147 | availability. This function is especially useful to enable an OPP which | |
148 | is not available by default. | |
149 | Example: In a case when SoC framework detects a situation where a | |
150 | higher frequency could be made available, it can use this function to | |
151 | find the OPP prior to call the opp_enable to actually make it available. | |
152 | rcu_read_lock(); | |
153 | opp = opp_find_freq_exact(dev, 1000000000, false); | |
154 | rcu_read_unlock(); | |
155 | /* dont operate on the pointer.. just do a sanity check.. */ | |
156 | if (IS_ERR(opp)) { | |
157 | pr_err("frequency not disabled!\n"); | |
158 | /* trigger appropriate actions.. */ | |
159 | } else { | |
160 | opp_enable(dev,1000000000); | |
161 | } | |
162 | ||
163 | NOTE: This is the only search function that operates on OPPs which are | |
164 | not available. | |
165 | ||
166 | opp_find_freq_floor - Search for an available OPP which is *at most* the | |
167 | provided frequency. This function is useful while searching for a lesser | |
168 | match OR operating on OPP information in the order of decreasing | |
169 | frequency. | |
170 | Example: To find the highest opp for a device: | |
171 | freq = ULONG_MAX; | |
172 | rcu_read_lock(); | |
173 | opp_find_freq_floor(dev, &freq); | |
174 | rcu_read_unlock(); | |
175 | ||
176 | opp_find_freq_ceil - Search for an available OPP which is *at least* the | |
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. | |
180 | Example 1: To find the lowest opp for a device: | |
181 | freq = 0; | |
182 | rcu_read_lock(); | |
183 | opp_find_freq_ceil(dev, &freq); | |
184 | rcu_read_unlock(); | |
185 | Example 2: A simplified implementation of a SoC cpufreq_driver->target: | |
186 | soc_cpufreq_target(..) | |
187 | { | |
188 | /* Do stuff like policy checks etc. */ | |
189 | /* Find the best frequency match for the req */ | |
190 | rcu_read_lock(); | |
191 | opp = opp_find_freq_ceil(dev, &freq); | |
192 | rcu_read_unlock(); | |
193 | if (!IS_ERR(opp)) | |
194 | soc_switch_to_freq_voltage(freq); | |
195 | else | |
25985edc | 196 | /* do something when we can't satisfy the req */ |
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197 | /* do other stuff */ |
198 | } | |
199 | ||
200 | 4. OPP Availability Control Functions | |
201 | ===================================== | |
202 | A default OPP list registered with the OPP library may not cater to all possible | |
203 | situation. The OPP library provides a set of functions to modify the | |
204 | availability of a OPP within the OPP list. This allows SoC frameworks to have | |
205 | fine grained dynamic control of which sets of OPPs are operationally available. | |
206 | These functions are intended to *temporarily* remove an OPP in conditions such | |
207 | as thermal considerations (e.g. don't use OPPx until the temperature drops). | |
208 | ||
209 | WARNING: Do not use these functions in interrupt context. | |
210 | ||
211 | opp_enable - Make a OPP available for operation. | |
212 | Example: Lets say that 1GHz OPP is to be made available only if the | |
213 | SoC temperature is lower than a certain threshold. The SoC framework | |
214 | implementation might choose to do something as follows: | |
215 | if (cur_temp < temp_low_thresh) { | |
216 | /* Enable 1GHz if it was disabled */ | |
217 | rcu_read_lock(); | |
218 | opp = opp_find_freq_exact(dev, 1000000000, false); | |
219 | rcu_read_unlock(); | |
220 | /* just error check */ | |
221 | if (!IS_ERR(opp)) | |
222 | ret = opp_enable(dev, 1000000000); | |
223 | else | |
224 | goto try_something_else; | |
225 | } | |
226 | ||
227 | opp_disable - Make an OPP to be not available for operation | |
228 | Example: Lets say that 1GHz OPP is to be disabled if the temperature | |
229 | exceeds a threshold value. The SoC framework implementation might | |
230 | choose to do something as follows: | |
231 | if (cur_temp > temp_high_thresh) { | |
232 | /* Disable 1GHz if it was enabled */ | |
233 | rcu_read_lock(); | |
234 | opp = opp_find_freq_exact(dev, 1000000000, true); | |
235 | rcu_read_unlock(); | |
236 | /* just error check */ | |
237 | if (!IS_ERR(opp)) | |
238 | ret = opp_disable(dev, 1000000000); | |
239 | else | |
240 | goto try_something_else; | |
241 | } | |
242 | ||
243 | 5. OPP Data Retrieval Functions | |
244 | =============================== | |
245 | Since OPP library abstracts away the OPP information, a set of functions to pull | |
246 | information from the OPP structure is necessary. Once an OPP pointer is | |
247 | retrieved using the search functions, the following functions can be used by SoC | |
248 | framework to retrieve the information represented inside the OPP layer. | |
249 | ||
250 | opp_get_voltage - Retrieve the voltage represented by the opp pointer. | |
251 | Example: At a cpufreq transition to a different frequency, SoC | |
252 | framework requires to set the voltage represented by the OPP using | |
253 | the regulator framework to the Power Management chip providing the | |
254 | voltage. | |
255 | soc_switch_to_freq_voltage(freq) | |
256 | { | |
257 | /* do things */ | |
258 | rcu_read_lock(); | |
259 | opp = opp_find_freq_ceil(dev, &freq); | |
260 | v = opp_get_voltage(opp); | |
261 | rcu_read_unlock(); | |
262 | if (v) | |
263 | regulator_set_voltage(.., v); | |
264 | /* do other things */ | |
265 | } | |
266 | ||
267 | opp_get_freq - Retrieve the freq represented by the opp pointer. | |
268 | Example: Lets say the SoC framework uses a couple of helper functions | |
269 | we could pass opp pointers instead of doing additional parameters to | |
270 | handle quiet a bit of data parameters. | |
271 | soc_cpufreq_target(..) | |
272 | { | |
273 | /* do things.. */ | |
274 | max_freq = ULONG_MAX; | |
275 | rcu_read_lock(); | |
276 | max_opp = opp_find_freq_floor(dev,&max_freq); | |
277 | requested_opp = opp_find_freq_ceil(dev,&freq); | |
278 | if (!IS_ERR(max_opp) && !IS_ERR(requested_opp)) | |
279 | r = soc_test_validity(max_opp, requested_opp); | |
280 | rcu_read_unlock(); | |
281 | /* do other things */ | |
282 | } | |
283 | soc_test_validity(..) | |
284 | { | |
285 | if(opp_get_voltage(max_opp) < opp_get_voltage(requested_opp)) | |
286 | return -EINVAL; | |
287 | if(opp_get_freq(max_opp) < opp_get_freq(requested_opp)) | |
288 | return -EINVAL; | |
289 | /* do things.. */ | |
290 | } | |
291 | ||
292 | opp_get_opp_count - Retrieve the number of available opps for a device | |
293 | Example: Lets say a co-processor in the SoC needs to know the available | |
294 | frequencies in a table, the main processor can notify as following: | |
295 | soc_notify_coproc_available_frequencies() | |
296 | { | |
297 | /* Do things */ | |
298 | rcu_read_lock(); | |
299 | num_available = opp_get_opp_count(dev); | |
300 | speeds = kzalloc(sizeof(u32) * num_available, GFP_KERNEL); | |
301 | /* populate the table in increasing order */ | |
302 | freq = 0; | |
303 | while (!IS_ERR(opp = opp_find_freq_ceil(dev, &freq))) { | |
304 | speeds[i] = freq; | |
305 | freq++; | |
306 | i++; | |
307 | } | |
308 | rcu_read_unlock(); | |
309 | ||
310 | soc_notify_coproc(AVAILABLE_FREQs, speeds, num_available); | |
311 | /* Do other things */ | |
312 | } | |
313 | ||
314 | 6. Cpufreq Table Generation | |
315 | =========================== | |
316 | opp_init_cpufreq_table - cpufreq framework typically is initialized with | |
317 | cpufreq_frequency_table_cpuinfo which is provided with the list of | |
318 | frequencies that are available for operation. This function provides | |
319 | a ready to use conversion routine to translate the OPP layer's internal | |
320 | information about the available frequencies into a format readily | |
321 | providable to cpufreq. | |
322 | ||
323 | WARNING: Do not use this function in interrupt context. | |
324 | ||
325 | Example: | |
326 | soc_pm_init() | |
327 | { | |
328 | /* Do things */ | |
329 | r = opp_init_cpufreq_table(dev, &freq_table); | |
330 | if (!r) | |
331 | cpufreq_frequency_table_cpuinfo(policy, freq_table); | |
332 | /* Do other things */ | |
333 | } | |
334 | ||
335 | NOTE: This function is available only if CONFIG_CPU_FREQ is enabled in | |
336 | addition to CONFIG_PM as power management feature is required to | |
337 | dynamically scale voltage and frequency in a system. | |
338 | ||
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339 | opp_free_cpufreq_table - Free up the table allocated by opp_init_cpufreq_table |
340 | ||
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341 | 7. Data Structures |
342 | ================== | |
343 | Typically an SoC contains multiple voltage domains which are variable. Each | |
344 | domain is represented by a device pointer. The relationship to OPP can be | |
345 | represented as follows: | |
346 | SoC | |
347 | |- device 1 | |
348 | | |- opp 1 (availability, freq, voltage) | |
349 | | |- opp 2 .. | |
350 | ... ... | |
351 | | `- opp n .. | |
352 | |- device 2 | |
353 | ... | |
354 | `- device m | |
355 | ||
356 | OPP library maintains a internal list that the SoC framework populates and | |
357 | accessed by various functions as described above. However, the structures | |
358 | representing the actual OPPs and domains are internal to the OPP library itself | |
359 | to allow for suitable abstraction reusable across systems. | |
360 | ||
361 | struct opp - The internal data structure of OPP library which is used to | |
362 | represent an OPP. In addition to the freq, voltage, availability | |
363 | information, it also contains internal book keeping information required | |
364 | for the OPP library to operate on. Pointer to this structure is | |
365 | provided back to the users such as SoC framework to be used as a | |
366 | identifier for OPP in the interactions with OPP layer. | |
367 | ||
368 | WARNING: The struct opp pointer should not be parsed or modified by the | |
369 | users. The defaults of for an instance is populated by opp_add, but the | |
370 | availability of the OPP can be modified by opp_enable/disable functions. | |
371 | ||
372 | struct device - This is used to identify a domain to the OPP layer. The | |
373 | nature of the device and it's implementation is left to the user of | |
374 | OPP library such as the SoC framework. | |
375 | ||
376 | Overall, in a simplistic view, the data structure operations is represented as | |
377 | following: | |
378 | ||
379 | Initialization / modification: | |
380 | +-----+ /- opp_enable | |
381 | opp_add --> | opp | <------- | |
382 | | +-----+ \- opp_disable | |
383 | \-------> domain_info(device) | |
384 | ||
385 | Search functions: | |
386 | /-- opp_find_freq_ceil ---\ +-----+ | |
387 | domain_info<---- opp_find_freq_exact -----> | opp | | |
388 | \-- opp_find_freq_floor ---/ +-----+ | |
389 | ||
390 | Retrieval functions: | |
391 | +-----+ /- opp_get_voltage | |
392 | | opp | <--- | |
393 | +-----+ \- opp_get_freq | |
394 | ||
395 | domain_info <- opp_get_opp_count |