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