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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 | ||
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82 | 2. Initial OPP List Registration |
83 | ================================ | |
5d4879cd | 84 | The SoC implementation calls dev_pm_opp_add function iteratively to add OPPs per |
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85 | device. It is expected that the SoC framework will register the OPP entries |
86 | optimally- typical numbers range to be less than 5. The list generated by | |
87 | registering the OPPs is maintained by OPP library throughout the device | |
88 | operation. The SoC framework can subsequently control the availability of the | |
5d4879cd | 89 | OPPs dynamically using the dev_pm_opp_enable / disable functions. |
e1f60b29 | 90 | |
5d4879cd | 91 | dev_pm_opp_add - Add a new OPP for a specific domain represented by the device pointer. |
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92 | The OPP is defined using the frequency and voltage. Once added, the OPP |
93 | is assumed to be available and control of it's availability can be done | |
5d4879cd | 94 | with the dev_pm_opp_enable/disable functions. OPP library internally stores |
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95 | and manages this information in the opp struct. This function may be |
96 | used by SoC framework to define a optimal list as per the demands of | |
97 | SoC usage environment. | |
98 | ||
99 | WARNING: Do not use this function in interrupt context. | |
100 | ||
101 | Example: | |
102 | soc_pm_init() | |
103 | { | |
104 | /* Do things */ | |
5d4879cd | 105 | r = dev_pm_opp_add(mpu_dev, 1000000, 900000); |
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106 | if (!r) { |
107 | pr_err("%s: unable to register mpu opp(%d)\n", r); | |
108 | goto no_cpufreq; | |
109 | } | |
110 | /* Do cpufreq things */ | |
111 | no_cpufreq: | |
112 | /* Do remaining things */ | |
113 | } | |
114 | ||
115 | 3. OPP Search Functions | |
116 | ======================= | |
117 | High level framework such as cpufreq operates on frequencies. To map the | |
118 | frequency back to the corresponding OPP, OPP library provides handy functions | |
119 | to search the OPP list that OPP library internally manages. These search | |
120 | functions return the matching pointer representing the opp if a match is | |
121 | found, else returns error. These errors are expected to be handled by standard | |
122 | error checks such as IS_ERR() and appropriate actions taken by the caller. | |
123 | ||
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124 | Callers of these functions shall call dev_pm_opp_put() after they have used the |
125 | OPP. Otherwise the memory for the OPP will never get freed and result in | |
126 | memleak. | |
127 | ||
5d4879cd | 128 | dev_pm_opp_find_freq_exact - Search for an OPP based on an *exact* frequency and |
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129 | availability. This function is especially useful to enable an OPP which |
130 | is not available by default. | |
131 | Example: In a case when SoC framework detects a situation where a | |
132 | higher frequency could be made available, it can use this function to | |
5d4879cd | 133 | find the OPP prior to call the dev_pm_opp_enable to actually make it available. |
5d4879cd | 134 | opp = dev_pm_opp_find_freq_exact(dev, 1000000000, false); |
6185deaa | 135 | dev_pm_opp_put(opp); |
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136 | /* dont operate on the pointer.. just do a sanity check.. */ |
137 | if (IS_ERR(opp)) { | |
138 | pr_err("frequency not disabled!\n"); | |
139 | /* trigger appropriate actions.. */ | |
140 | } else { | |
5d4879cd | 141 | dev_pm_opp_enable(dev,1000000000); |
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142 | } |
143 | ||
144 | NOTE: This is the only search function that operates on OPPs which are | |
145 | not available. | |
146 | ||
5d4879cd | 147 | dev_pm_opp_find_freq_floor - Search for an available OPP which is *at most* the |
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148 | provided frequency. This function is useful while searching for a lesser |
149 | match OR operating on OPP information in the order of decreasing | |
150 | frequency. | |
151 | Example: To find the highest opp for a device: | |
152 | freq = ULONG_MAX; | |
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153 | opp = dev_pm_opp_find_freq_floor(dev, &freq); |
154 | dev_pm_opp_put(opp); | |
e1f60b29 | 155 | |
5d4879cd | 156 | dev_pm_opp_find_freq_ceil - Search for an available OPP which is *at least* the |
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157 | provided frequency. This function is useful while searching for a |
158 | higher match OR operating on OPP information in the order of increasing | |
159 | frequency. | |
160 | Example 1: To find the lowest opp for a device: | |
161 | freq = 0; | |
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162 | opp = dev_pm_opp_find_freq_ceil(dev, &freq); |
163 | dev_pm_opp_put(opp); | |
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164 | Example 2: A simplified implementation of a SoC cpufreq_driver->target: |
165 | soc_cpufreq_target(..) | |
166 | { | |
167 | /* Do stuff like policy checks etc. */ | |
168 | /* Find the best frequency match for the req */ | |
5d4879cd | 169 | opp = dev_pm_opp_find_freq_ceil(dev, &freq); |
6185deaa | 170 | dev_pm_opp_put(opp); |
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171 | if (!IS_ERR(opp)) |
172 | soc_switch_to_freq_voltage(freq); | |
173 | else | |
25985edc | 174 | /* do something when we can't satisfy the req */ |
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175 | /* do other stuff */ |
176 | } | |
177 | ||
178 | 4. OPP Availability Control Functions | |
179 | ===================================== | |
180 | A default OPP list registered with the OPP library may not cater to all possible | |
181 | situation. The OPP library provides a set of functions to modify the | |
182 | availability of a OPP within the OPP list. This allows SoC frameworks to have | |
183 | fine grained dynamic control of which sets of OPPs are operationally available. | |
184 | These functions are intended to *temporarily* remove an OPP in conditions such | |
185 | as thermal considerations (e.g. don't use OPPx until the temperature drops). | |
186 | ||
187 | WARNING: Do not use these functions in interrupt context. | |
188 | ||
5d4879cd | 189 | dev_pm_opp_enable - Make a OPP available for operation. |
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190 | Example: Lets say that 1GHz OPP is to be made available only if the |
191 | SoC temperature is lower than a certain threshold. The SoC framework | |
192 | implementation might choose to do something as follows: | |
193 | if (cur_temp < temp_low_thresh) { | |
194 | /* Enable 1GHz if it was disabled */ | |
5d4879cd | 195 | opp = dev_pm_opp_find_freq_exact(dev, 1000000000, false); |
6185deaa | 196 | dev_pm_opp_put(opp); |
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197 | /* just error check */ |
198 | if (!IS_ERR(opp)) | |
5d4879cd | 199 | ret = dev_pm_opp_enable(dev, 1000000000); |
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200 | else |
201 | goto try_something_else; | |
202 | } | |
203 | ||
5d4879cd | 204 | dev_pm_opp_disable - Make an OPP to be not available for operation |
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205 | Example: Lets say that 1GHz OPP is to be disabled if the temperature |
206 | exceeds a threshold value. The SoC framework implementation might | |
207 | choose to do something as follows: | |
208 | if (cur_temp > temp_high_thresh) { | |
209 | /* Disable 1GHz if it was enabled */ | |
5d4879cd | 210 | opp = dev_pm_opp_find_freq_exact(dev, 1000000000, true); |
6185deaa | 211 | dev_pm_opp_put(opp); |
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212 | /* just error check */ |
213 | if (!IS_ERR(opp)) | |
5d4879cd | 214 | ret = dev_pm_opp_disable(dev, 1000000000); |
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215 | else |
216 | goto try_something_else; | |
217 | } | |
218 | ||
219 | 5. OPP Data Retrieval Functions | |
220 | =============================== | |
221 | Since OPP library abstracts away the OPP information, a set of functions to pull | |
222 | information from the OPP structure is necessary. Once an OPP pointer is | |
223 | retrieved using the search functions, the following functions can be used by SoC | |
224 | framework to retrieve the information represented inside the OPP layer. | |
225 | ||
5d4879cd | 226 | dev_pm_opp_get_voltage - Retrieve the voltage represented by the opp pointer. |
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227 | Example: At a cpufreq transition to a different frequency, SoC |
228 | framework requires to set the voltage represented by the OPP using | |
229 | the regulator framework to the Power Management chip providing the | |
230 | voltage. | |
231 | soc_switch_to_freq_voltage(freq) | |
232 | { | |
233 | /* do things */ | |
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234 | opp = dev_pm_opp_find_freq_ceil(dev, &freq); |
235 | v = dev_pm_opp_get_voltage(opp); | |
6185deaa | 236 | dev_pm_opp_put(opp); |
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237 | if (v) |
238 | regulator_set_voltage(.., v); | |
239 | /* do other things */ | |
240 | } | |
241 | ||
5d4879cd | 242 | dev_pm_opp_get_freq - Retrieve the freq represented by the opp pointer. |
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243 | Example: Lets say the SoC framework uses a couple of helper functions |
244 | we could pass opp pointers instead of doing additional parameters to | |
245 | handle quiet a bit of data parameters. | |
246 | soc_cpufreq_target(..) | |
247 | { | |
248 | /* do things.. */ | |
249 | max_freq = ULONG_MAX; | |
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250 | max_opp = dev_pm_opp_find_freq_floor(dev,&max_freq); |
251 | requested_opp = dev_pm_opp_find_freq_ceil(dev,&freq); | |
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252 | if (!IS_ERR(max_opp) && !IS_ERR(requested_opp)) |
253 | r = soc_test_validity(max_opp, requested_opp); | |
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254 | dev_pm_opp_put(max_opp); |
255 | dev_pm_opp_put(requested_opp); | |
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256 | /* do other things */ |
257 | } | |
258 | soc_test_validity(..) | |
259 | { | |
5d4879cd | 260 | if(dev_pm_opp_get_voltage(max_opp) < dev_pm_opp_get_voltage(requested_opp)) |
e1f60b29 | 261 | return -EINVAL; |
5d4879cd | 262 | if(dev_pm_opp_get_freq(max_opp) < dev_pm_opp_get_freq(requested_opp)) |
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263 | return -EINVAL; |
264 | /* do things.. */ | |
265 | } | |
266 | ||
5d4879cd | 267 | dev_pm_opp_get_opp_count - Retrieve the number of available opps for a device |
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268 | Example: Lets say a co-processor in the SoC needs to know the available |
269 | frequencies in a table, the main processor can notify as following: | |
270 | soc_notify_coproc_available_frequencies() | |
271 | { | |
272 | /* Do things */ | |
5d4879cd | 273 | num_available = dev_pm_opp_get_opp_count(dev); |
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274 | speeds = kzalloc(sizeof(u32) * num_available, GFP_KERNEL); |
275 | /* populate the table in increasing order */ | |
276 | freq = 0; | |
5d4879cd | 277 | while (!IS_ERR(opp = dev_pm_opp_find_freq_ceil(dev, &freq))) { |
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278 | speeds[i] = freq; |
279 | freq++; | |
280 | i++; | |
6185deaa | 281 | dev_pm_opp_put(opp); |
e1f60b29 | 282 | } |
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283 | |
284 | soc_notify_coproc(AVAILABLE_FREQs, speeds, num_available); | |
285 | /* Do other things */ | |
286 | } | |
287 | ||
a0dd7b79 | 288 | 6. Data Structures |
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289 | ================== |
290 | Typically an SoC contains multiple voltage domains which are variable. Each | |
291 | domain is represented by a device pointer. The relationship to OPP can be | |
292 | represented as follows: | |
293 | SoC | |
294 | |- device 1 | |
295 | | |- opp 1 (availability, freq, voltage) | |
296 | | |- opp 2 .. | |
297 | ... ... | |
298 | | `- opp n .. | |
299 | |- device 2 | |
300 | ... | |
301 | `- device m | |
302 | ||
303 | OPP library maintains a internal list that the SoC framework populates and | |
304 | accessed by various functions as described above. However, the structures | |
305 | representing the actual OPPs and domains are internal to the OPP library itself | |
306 | to allow for suitable abstraction reusable across systems. | |
307 | ||
47d43ba7 | 308 | struct dev_pm_opp - The internal data structure of OPP library which is used to |
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309 | represent an OPP. In addition to the freq, voltage, availability |
310 | information, it also contains internal book keeping information required | |
311 | for the OPP library to operate on. Pointer to this structure is | |
312 | provided back to the users such as SoC framework to be used as a | |
313 | identifier for OPP in the interactions with OPP layer. | |
314 | ||
47d43ba7 | 315 | WARNING: The struct dev_pm_opp pointer should not be parsed or modified by the |
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316 | users. The defaults of for an instance is populated by dev_pm_opp_add, but the |
317 | availability of the OPP can be modified by dev_pm_opp_enable/disable functions. | |
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318 | |
319 | struct device - This is used to identify a domain to the OPP layer. The | |
320 | nature of the device and it's implementation is left to the user of | |
321 | OPP library such as the SoC framework. | |
322 | ||
323 | Overall, in a simplistic view, the data structure operations is represented as | |
324 | following: | |
325 | ||
326 | Initialization / modification: | |
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327 | +-----+ /- dev_pm_opp_enable |
328 | dev_pm_opp_add --> | opp | <------- | |
329 | | +-----+ \- dev_pm_opp_disable | |
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330 | \-------> domain_info(device) |
331 | ||
332 | Search functions: | |
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333 | /-- dev_pm_opp_find_freq_ceil ---\ +-----+ |
334 | domain_info<---- dev_pm_opp_find_freq_exact -----> | opp | | |
335 | \-- dev_pm_opp_find_freq_floor ---/ +-----+ | |
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336 | |
337 | Retrieval functions: | |
5d4879cd | 338 | +-----+ /- dev_pm_opp_get_voltage |
e1f60b29 | 339 | | opp | <--- |
5d4879cd | 340 | +-----+ \- dev_pm_opp_get_freq |
e1f60b29 | 341 | |
5d4879cd | 342 | domain_info <- dev_pm_opp_get_opp_count |