drivers/cpufreq/amd-pstate.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /*
   3  * amd-pstate.c - AMD Processor P-state Frequency Driver
   4  *
   5  * Copyright (C) 2021 Advanced Micro Devices, Inc. All Rights Reserved.
   6  *
   7  * Author: Huang Rui <ray.huang@amd.com>
   8  *
   9  * AMD P-State introduces a new CPU performance scaling design for AMD
  10  * processors using the ACPI Collaborative Performance and Power Control (CPPC)
  11  * feature which works with the AMD SMU firmware providing a finer grained
  12  * frequency control range. It is to replace the legacy ACPI P-States control,
  13  * allows a flexible, low-latency interface for the Linux kernel to directly
  14  * communicate the performance hints to hardware.
  15  *
  16  * AMD P-State is supported on recent AMD Zen base CPU series include some of
  17  * Zen2 and Zen3 processors. _CPC needs to be present in the ACPI tables of AMD
  18  * P-State supported system. And there are two types of hardware implementations
  19  * for AMD P-State: 1) Full MSR Solution and 2) Shared Memory Solution.
  20  * X86_FEATURE_CPPC CPU feature flag is used to distinguish the different types.
  21  */
  22
  23 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  24
  25 #include <linux/kernel.h>
  26 #include <linux/module.h>
  27 #include <linux/init.h>
  28 #include <linux/smp.h>
  29 #include <linux/sched.h>
  30 #include <linux/cpufreq.h>
  31 #include <linux/compiler.h>
  32 #include <linux/dmi.h>
  33 #include <linux/slab.h>
  34 #include <linux/acpi.h>
  35 #include <linux/io.h>
  36 #include <linux/delay.h>
  37 #include <linux/uaccess.h>
  38 #include <linux/static_call.h>
  39 #include <linux/amd-pstate.h>
  40
  41 #include <acpi/processor.h>
  42 #include <acpi/cppc_acpi.h>
  43
  44 #include <asm/msr.h>
  45 #include <asm/processor.h>
  46 #include <asm/cpufeature.h>
  47 #include <asm/cpu_device_id.h>
  48 #include "amd-pstate-trace.h"
  49
  50 #define AMD_PSTATE_TRANSITION_LATENCY   20000
  51 #define AMD_PSTATE_TRANSITION_DELAY     1000
  52
  53 /*
  54  * TODO: We need more time to fine tune processors with shared memory solution
  55  * with community together.
  56  *
  57  * There are some performance drops on the CPU benchmarks which reports from
  58  * Suse. We are co-working with them to fine tune the shared memory solution. So
  59  * we disable it by default to go acpi-cpufreq on these processors and add a
  60  * module parameter to be able to enable it manually for debugging.
  61  */
  62 static struct cpufreq_driver amd_pstate_driver;
  63 static int cppc_load __initdata;
  64
  65 static inline int pstate_enable(bool enable)
  66 {
  67         return wrmsrl_safe(MSR_AMD_CPPC_ENABLE, enable);
  68 }
  69
  70 static int cppc_enable(bool enable)
  71 {
  72         int cpu, ret = 0;
  73
  74         for_each_present_cpu(cpu) {
  75                 ret = cppc_set_enable(cpu, enable);
  76                 if (ret)
  77                         return ret;
  78         }
  79
  80         return ret;
  81 }
  82
  83 DEFINE_STATIC_CALL(amd_pstate_enable, pstate_enable);
  84
  85 static inline int amd_pstate_enable(bool enable)
  86 {
  87         return static_call(amd_pstate_enable)(enable);
  88 }
  89
  90 static int pstate_init_perf(struct amd_cpudata *cpudata)
  91 {
  92         u64 cap1;
  93         u32 highest_perf;
  94
  95         int ret = rdmsrl_safe_on_cpu(cpudata->cpu, MSR_AMD_CPPC_CAP1,
  96                                      &cap1);
  97         if (ret)
  98                 return ret;
  99
 100         /*
 101          * TODO: Introduce AMD specific power feature.
 102          *
 103          * CPPC entry doesn't indicate the highest performance in some ASICs.
 104          */
 105         highest_perf = amd_get_highest_perf();
 106         if (highest_perf > AMD_CPPC_HIGHEST_PERF(cap1))
 107                 highest_perf = AMD_CPPC_HIGHEST_PERF(cap1);
 108
 109         WRITE_ONCE(cpudata->highest_perf, highest_perf);
 110
 111         WRITE_ONCE(cpudata->nominal_perf, AMD_CPPC_NOMINAL_PERF(cap1));
 112         WRITE_ONCE(cpudata->lowest_nonlinear_perf, AMD_CPPC_LOWNONLIN_PERF(cap1));
 113         WRITE_ONCE(cpudata->lowest_perf, AMD_CPPC_LOWEST_PERF(cap1));
 114
 115         return 0;
 116 }
 117
 118 static int cppc_init_perf(struct amd_cpudata *cpudata)
 119 {
 120         struct cppc_perf_caps cppc_perf;
 121         u32 highest_perf;
 122
 123         int ret = cppc_get_perf_caps(cpudata->cpu, &cppc_perf);
 124         if (ret)
 125                 return ret;
 126
 127         highest_perf = amd_get_highest_perf();
 128         if (highest_perf > cppc_perf.highest_perf)
 129                 highest_perf = cppc_perf.highest_perf;
 130
 131         WRITE_ONCE(cpudata->highest_perf, highest_perf);
 132
 133         WRITE_ONCE(cpudata->nominal_perf, cppc_perf.nominal_perf);
 134         WRITE_ONCE(cpudata->lowest_nonlinear_perf,
 135                    cppc_perf.lowest_nonlinear_perf);
 136         WRITE_ONCE(cpudata->lowest_perf, cppc_perf.lowest_perf);
 137
 138         return 0;
 139 }
 140
 141 DEFINE_STATIC_CALL(amd_pstate_init_perf, pstate_init_perf);
 142
 143 static inline int amd_pstate_init_perf(struct amd_cpudata *cpudata)
 144 {
 145         return static_call(amd_pstate_init_perf)(cpudata);
 146 }
 147
 148 static void pstate_update_perf(struct amd_cpudata *cpudata, u32 min_perf,
 149                                u32 des_perf, u32 max_perf, bool fast_switch)
 150 {
 151         if (fast_switch)
 152                 wrmsrl(MSR_AMD_CPPC_REQ, READ_ONCE(cpudata->cppc_req_cached));
 153         else
 154                 wrmsrl_on_cpu(cpudata->cpu, MSR_AMD_CPPC_REQ,
 155                               READ_ONCE(cpudata->cppc_req_cached));
 156 }
 157
 158 static void cppc_update_perf(struct amd_cpudata *cpudata,
 159                              u32 min_perf, u32 des_perf,
 160                              u32 max_perf, bool fast_switch)
 161 {
 162         struct cppc_perf_ctrls perf_ctrls;
 163
 164         perf_ctrls.max_perf = max_perf;
 165         perf_ctrls.min_perf = min_perf;
 166         perf_ctrls.desired_perf = des_perf;
 167
 168         cppc_set_perf(cpudata->cpu, &perf_ctrls);
 169 }
 170
 171 DEFINE_STATIC_CALL(amd_pstate_update_perf, pstate_update_perf);
 172
 173 static inline void amd_pstate_update_perf(struct amd_cpudata *cpudata,
 174                                           u32 min_perf, u32 des_perf,
 175                                           u32 max_perf, bool fast_switch)
 176 {
 177         static_call(amd_pstate_update_perf)(cpudata, min_perf, des_perf,
 178                                             max_perf, fast_switch);
 179 }
 180
 181 static inline bool amd_pstate_sample(struct amd_cpudata *cpudata)
 182 {
 183         u64 aperf, mperf, tsc;
 184         unsigned long flags;
 185
 186         local_irq_save(flags);
 187         rdmsrl(MSR_IA32_APERF, aperf);
 188         rdmsrl(MSR_IA32_MPERF, mperf);
 189         tsc = rdtsc();
 190
 191         if (cpudata->prev.mperf == mperf || cpudata->prev.tsc == tsc) {
 192                 local_irq_restore(flags);
 193                 return false;
 194         }
 195
 196         local_irq_restore(flags);
 197
 198         cpudata->cur.aperf = aperf;
 199         cpudata->cur.mperf = mperf;
 200         cpudata->cur.tsc =  tsc;
 201         cpudata->cur.aperf -= cpudata->prev.aperf;
 202         cpudata->cur.mperf -= cpudata->prev.mperf;
 203         cpudata->cur.tsc -= cpudata->prev.tsc;
 204
 205         cpudata->prev.aperf = aperf;
 206         cpudata->prev.mperf = mperf;
 207         cpudata->prev.tsc = tsc;
 208
 209         cpudata->freq = div64_u64((cpudata->cur.aperf * cpu_khz), cpudata->cur.mperf);
 210
 211         return true;
 212 }
 213
 214 static void amd_pstate_update(struct amd_cpudata *cpudata, u32 min_perf,
 215                               u32 des_perf, u32 max_perf, bool fast_switch)
 216 {
 217         u64 prev = READ_ONCE(cpudata->cppc_req_cached);
 218         u64 value = prev;
 219
 220         des_perf = clamp_t(unsigned long, des_perf, min_perf, max_perf);
 221         value &= ~AMD_CPPC_MIN_PERF(~0L);
 222         value |= AMD_CPPC_MIN_PERF(min_perf);
 223
 224         value &= ~AMD_CPPC_DES_PERF(~0L);
 225         value |= AMD_CPPC_DES_PERF(des_perf);
 226
 227         value &= ~AMD_CPPC_MAX_PERF(~0L);
 228         value |= AMD_CPPC_MAX_PERF(max_perf);
 229
 230         if (trace_amd_pstate_perf_enabled() && amd_pstate_sample(cpudata)) {
 231                 trace_amd_pstate_perf(min_perf, des_perf, max_perf, cpudata->freq,
 232                         cpudata->cur.mperf, cpudata->cur.aperf, cpudata->cur.tsc,
 233                                 cpudata->cpu, (value != prev), fast_switch);
 234         }
 235
 236         if (value == prev)
 237                 return;
 238
 239         WRITE_ONCE(cpudata->cppc_req_cached, value);
 240
 241         amd_pstate_update_perf(cpudata, min_perf, des_perf,
 242                                max_perf, fast_switch);
 243 }
 244
 245 static int amd_pstate_verify(struct cpufreq_policy_data *policy)
 246 {
 247         cpufreq_verify_within_cpu_limits(policy);
 248
 249         return 0;
 250 }
 251
 252 static int amd_pstate_target(struct cpufreq_policy *policy,
 253                              unsigned int target_freq,
 254                              unsigned int relation)
 255 {
 256         struct cpufreq_freqs freqs;
 257         struct amd_cpudata *cpudata = policy->driver_data;
 258         unsigned long max_perf, min_perf, des_perf, cap_perf;
 259
 260         if (!cpudata->max_freq)
 261                 return -ENODEV;
 262
 263         cap_perf = READ_ONCE(cpudata->highest_perf);
 264         min_perf = READ_ONCE(cpudata->lowest_perf);
 265         max_perf = cap_perf;
 266
 267         freqs.old = policy->cur;
 268         freqs.new = target_freq;
 269
 270         des_perf = DIV_ROUND_CLOSEST(target_freq * cap_perf,
 271                                      cpudata->max_freq);
 272
 273         cpufreq_freq_transition_begin(policy, &freqs);
 274         amd_pstate_update(cpudata, min_perf, des_perf,
 275                           max_perf, false);
 276         cpufreq_freq_transition_end(policy, &freqs, false);
 277
 278         return 0;
 279 }
 280
 281 static void amd_pstate_adjust_perf(unsigned int cpu,
 282                                    unsigned long _min_perf,
 283                                    unsigned long target_perf,
 284                                    unsigned long capacity)
 285 {
 286         unsigned long max_perf, min_perf, des_perf,
 287                       cap_perf, lowest_nonlinear_perf;
 288         struct cpufreq_policy *policy = cpufreq_cpu_get(cpu);
 289         struct amd_cpudata *cpudata = policy->driver_data;
 290
 291         cap_perf = READ_ONCE(cpudata->highest_perf);
 292         lowest_nonlinear_perf = READ_ONCE(cpudata->lowest_nonlinear_perf);
 293
 294         des_perf = cap_perf;
 295         if (target_perf < capacity)
 296                 des_perf = DIV_ROUND_UP(cap_perf * target_perf, capacity);
 297
 298         min_perf = READ_ONCE(cpudata->highest_perf);
 299         if (_min_perf < capacity)
 300                 min_perf = DIV_ROUND_UP(cap_perf * _min_perf, capacity);
 301
 302         if (min_perf < lowest_nonlinear_perf)
 303                 min_perf = lowest_nonlinear_perf;
 304
 305         max_perf = cap_perf;
 306         if (max_perf < min_perf)
 307                 max_perf = min_perf;
 308
 309         amd_pstate_update(cpudata, min_perf, des_perf, max_perf, true);
 310 }
 311
 312 static int amd_get_min_freq(struct amd_cpudata *cpudata)
 313 {
 314         struct cppc_perf_caps cppc_perf;
 315
 316         int ret = cppc_get_perf_caps(cpudata->cpu, &cppc_perf);
 317         if (ret)
 318                 return ret;
 319
 320         /* Switch to khz */
 321         return cppc_perf.lowest_freq * 1000;
 322 }
 323
 324 static int amd_get_max_freq(struct amd_cpudata *cpudata)
 325 {
 326         struct cppc_perf_caps cppc_perf;
 327         u32 max_perf, max_freq, nominal_freq, nominal_perf;
 328         u64 boost_ratio;
 329
 330         int ret = cppc_get_perf_caps(cpudata->cpu, &cppc_perf);
 331         if (ret)
 332                 return ret;
 333
 334         nominal_freq = cppc_perf.nominal_freq;
 335         nominal_perf = READ_ONCE(cpudata->nominal_perf);
 336         max_perf = READ_ONCE(cpudata->highest_perf);
 337
 338         boost_ratio = div_u64(max_perf << SCHED_CAPACITY_SHIFT,
 339                               nominal_perf);
 340
 341         max_freq = nominal_freq * boost_ratio >> SCHED_CAPACITY_SHIFT;
 342
 343         /* Switch to khz */
 344         return max_freq * 1000;
 345 }
 346
 347 static int amd_get_nominal_freq(struct amd_cpudata *cpudata)
 348 {
 349         struct cppc_perf_caps cppc_perf;
 350
 351         int ret = cppc_get_perf_caps(cpudata->cpu, &cppc_perf);
 352         if (ret)
 353                 return ret;
 354
 355         /* Switch to khz */
 356         return cppc_perf.nominal_freq * 1000;
 357 }
 358
 359 static int amd_get_lowest_nonlinear_freq(struct amd_cpudata *cpudata)
 360 {
 361         struct cppc_perf_caps cppc_perf;
 362         u32 lowest_nonlinear_freq, lowest_nonlinear_perf,
 363             nominal_freq, nominal_perf;
 364         u64 lowest_nonlinear_ratio;
 365
 366         int ret = cppc_get_perf_caps(cpudata->cpu, &cppc_perf);
 367         if (ret)
 368                 return ret;
 369
 370         nominal_freq = cppc_perf.nominal_freq;
 371         nominal_perf = READ_ONCE(cpudata->nominal_perf);
 372
 373         lowest_nonlinear_perf = cppc_perf.lowest_nonlinear_perf;
 374
 375         lowest_nonlinear_ratio = div_u64(lowest_nonlinear_perf << SCHED_CAPACITY_SHIFT,
 376                                          nominal_perf);
 377
 378         lowest_nonlinear_freq = nominal_freq * lowest_nonlinear_ratio >> SCHED_CAPACITY_SHIFT;
 379
 380         /* Switch to khz */
 381         return lowest_nonlinear_freq * 1000;
 382 }
 383
 384 static int amd_pstate_set_boost(struct cpufreq_policy *policy, int state)
 385 {
 386         struct amd_cpudata *cpudata = policy->driver_data;
 387         int ret;
 388
 389         if (!cpudata->boost_supported) {
 390                 pr_err("Boost mode is not supported by this processor or SBIOS\n");
 391                 return -EINVAL;
 392         }
 393
 394         if (state)
 395                 policy->cpuinfo.max_freq = cpudata->max_freq;
 396         else
 397                 policy->cpuinfo.max_freq = cpudata->nominal_freq;
 398
 399         policy->max = policy->cpuinfo.max_freq;
 400
 401         ret = freq_qos_update_request(&cpudata->req[1],
 402                                       policy->cpuinfo.max_freq);
 403         if (ret < 0)
 404                 return ret;
 405
 406         return 0;
 407 }
 408
 409 static void amd_pstate_boost_init(struct amd_cpudata *cpudata)
 410 {
 411         u32 highest_perf, nominal_perf;
 412
 413         highest_perf = READ_ONCE(cpudata->highest_perf);
 414         nominal_perf = READ_ONCE(cpudata->nominal_perf);
 415
 416         if (highest_perf <= nominal_perf)
 417                 return;
 418
 419         cpudata->boost_supported = true;
 420         amd_pstate_driver.boost_enabled = true;
 421 }
 422
 423 static void amd_perf_ctl_reset(unsigned int cpu)
 424 {
 425         wrmsrl_on_cpu(cpu, MSR_AMD_PERF_CTL, 0);
 426 }
 427
 428 static int amd_pstate_cpu_init(struct cpufreq_policy *policy)
 429 {
 430         int min_freq, max_freq, nominal_freq, lowest_nonlinear_freq, ret;
 431         struct device *dev;
 432         struct amd_cpudata *cpudata;
 433
 434         /*
 435          * Resetting PERF_CTL_MSR will put the CPU in P0 frequency,
 436          * which is ideal for initialization process.
 437          */
 438         amd_perf_ctl_reset(policy->cpu);
 439         dev = get_cpu_device(policy->cpu);
 440         if (!dev)
 441                 return -ENODEV;
 442
 443         cpudata = kzalloc(sizeof(*cpudata), GFP_KERNEL);
 444         if (!cpudata)
 445                 return -ENOMEM;
 446
 447         cpudata->cpu = policy->cpu;
 448
 449         ret = amd_pstate_init_perf(cpudata);
 450         if (ret)
 451                 goto free_cpudata1;
 452
 453         min_freq = amd_get_min_freq(cpudata);
 454         max_freq = amd_get_max_freq(cpudata);
 455         nominal_freq = amd_get_nominal_freq(cpudata);
 456         lowest_nonlinear_freq = amd_get_lowest_nonlinear_freq(cpudata);
 457
 458         if (min_freq < 0 || max_freq < 0 || min_freq > max_freq) {
 459                 dev_err(dev, "min_freq(%d) or max_freq(%d) value is incorrect\n",
 460                         min_freq, max_freq);
 461                 ret = -EINVAL;
 462                 goto free_cpudata1;
 463         }
 464
 465         policy->cpuinfo.transition_latency = AMD_PSTATE_TRANSITION_LATENCY;
 466         policy->transition_delay_us = AMD_PSTATE_TRANSITION_DELAY;
 467
 468         policy->min = min_freq;
 469         policy->max = max_freq;
 470
 471         policy->cpuinfo.min_freq = min_freq;
 472         policy->cpuinfo.max_freq = max_freq;
 473
 474         /* It will be updated by governor */
 475         policy->cur = policy->cpuinfo.min_freq;
 476
 477         if (boot_cpu_has(X86_FEATURE_CPPC))
 478                 policy->fast_switch_possible = true;
 479
 480         ret = freq_qos_add_request(&policy->constraints, &cpudata->req[0],
 481                                    FREQ_QOS_MIN, policy->cpuinfo.min_freq);
 482         if (ret < 0) {
 483                 dev_err(dev, "Failed to add min-freq constraint (%d)\n", ret);
 484                 goto free_cpudata1;
 485         }
 486
 487         ret = freq_qos_add_request(&policy->constraints, &cpudata->req[1],
 488                                    FREQ_QOS_MAX, policy->cpuinfo.max_freq);
 489         if (ret < 0) {
 490                 dev_err(dev, "Failed to add max-freq constraint (%d)\n", ret);
 491                 goto free_cpudata2;
 492         }
 493
 494         /* Initial processor data capability frequencies */
 495         cpudata->max_freq = max_freq;
 496         cpudata->min_freq = min_freq;
 497         cpudata->nominal_freq = nominal_freq;
 498         cpudata->lowest_nonlinear_freq = lowest_nonlinear_freq;
 499
 500         policy->driver_data = cpudata;
 501
 502         amd_pstate_boost_init(cpudata);
 503
 504         return 0;
 505
 506 free_cpudata2:
 507         freq_qos_remove_request(&cpudata->req[0]);
 508 free_cpudata1:
 509         kfree(cpudata);
 510         return ret;
 511 }
 512
 513 static int amd_pstate_cpu_exit(struct cpufreq_policy *policy)
 514 {
 515         struct amd_cpudata *cpudata = policy->driver_data;
 516
 517         freq_qos_remove_request(&cpudata->req[1]);
 518         freq_qos_remove_request(&cpudata->req[0]);
 519         kfree(cpudata);
 520
 521         return 0;
 522 }
 523
 524 static int amd_pstate_cpu_resume(struct cpufreq_policy *policy)
 525 {
 526         int ret;
 527
 528         ret = amd_pstate_enable(true);
 529         if (ret)
 530                 pr_err("failed to enable amd-pstate during resume, return %d\n", ret);
 531
 532         return ret;
 533 }
 534
 535 static int amd_pstate_cpu_suspend(struct cpufreq_policy *policy)
 536 {
 537         int ret;
 538
 539         ret = amd_pstate_enable(false);
 540         if (ret)
 541                 pr_err("failed to disable amd-pstate during suspend, return %d\n", ret);
 542
 543         return ret;
 544 }
 545
 546 /* Sysfs attributes */
 547
 548 /*
 549  * This frequency is to indicate the maximum hardware frequency.
 550  * If boost is not active but supported, the frequency will be larger than the
 551  * one in cpuinfo.
 552  */
 553 static ssize_t show_amd_pstate_max_freq(struct cpufreq_policy *policy,
 554                                         char *buf)
 555 {
 556         int max_freq;
 557         struct amd_cpudata *cpudata = policy->driver_data;
 558
 559         max_freq = amd_get_max_freq(cpudata);
 560         if (max_freq < 0)
 561                 return max_freq;
 562
 563         return sprintf(&buf[0], "%u\n", max_freq);
 564 }
 565
 566 static ssize_t show_amd_pstate_lowest_nonlinear_freq(struct cpufreq_policy *policy,
 567                                                      char *buf)
 568 {
 569         int freq;
 570         struct amd_cpudata *cpudata = policy->driver_data;
 571
 572         freq = amd_get_lowest_nonlinear_freq(cpudata);
 573         if (freq < 0)
 574                 return freq;
 575
 576         return sprintf(&buf[0], "%u\n", freq);
 577 }
 578
 579 /*
 580  * In some of ASICs, the highest_perf is not the one in the _CPC table, so we
 581  * need to expose it to sysfs.
 582  */
 583 static ssize_t show_amd_pstate_highest_perf(struct cpufreq_policy *policy,
 584                                             char *buf)
 585 {
 586         u32 perf;
 587         struct amd_cpudata *cpudata = policy->driver_data;
 588
 589         perf = READ_ONCE(cpudata->highest_perf);
 590
 591         return sprintf(&buf[0], "%u\n", perf);
 592 }
 593
 594 cpufreq_freq_attr_ro(amd_pstate_max_freq);
 595 cpufreq_freq_attr_ro(amd_pstate_lowest_nonlinear_freq);
 596
 597 cpufreq_freq_attr_ro(amd_pstate_highest_perf);
 598
 599 static struct freq_attr *amd_pstate_attr[] = {
 600         &amd_pstate_max_freq,
 601         &amd_pstate_lowest_nonlinear_freq,
 602         &amd_pstate_highest_perf,
 603         NULL,
 604 };
 605
 606 static struct cpufreq_driver amd_pstate_driver = {
 607         .flags          = CPUFREQ_CONST_LOOPS | CPUFREQ_NEED_UPDATE_LIMITS,
 608         .verify         = amd_pstate_verify,
 609         .target         = amd_pstate_target,
 610         .init           = amd_pstate_cpu_init,
 611         .exit           = amd_pstate_cpu_exit,
 612         .suspend        = amd_pstate_cpu_suspend,
 613         .resume         = amd_pstate_cpu_resume,
 614         .set_boost      = amd_pstate_set_boost,
 615         .name           = "amd-pstate",
 616         .attr           = amd_pstate_attr,
 617 };
 618
 619 static int __init amd_pstate_init(void)
 620 {
 621         int ret;
 622
 623         if (boot_cpu_data.x86_vendor != X86_VENDOR_AMD)
 624                 return -ENODEV;
 625         /*
 626          * by default the pstate driver is disabled to load
 627          * enable the amd_pstate passive mode driver explicitly
 628          * with amd_pstate=passive in kernel command line
 629          */
 630         if (!cppc_load) {
 631                 pr_debug("driver load is disabled, boot with amd_pstate=passive to enable this\n");
 632                 return -ENODEV;
 633         }
 634
 635         if (!acpi_cpc_valid()) {
 636                 pr_warn_once("the _CPC object is not present in SBIOS or ACPI disabled\n");
 637                 return -ENODEV;
 638         }
 639
 640         /* don't keep reloading if cpufreq_driver exists */
 641         if (cpufreq_get_current_driver())
 642                 return -EEXIST;
 643
 644         /* capability check */
 645         if (boot_cpu_has(X86_FEATURE_CPPC)) {
 646                 pr_debug("AMD CPPC MSR based functionality is supported\n");
 647                 amd_pstate_driver.adjust_perf = amd_pstate_adjust_perf;
 648         } else {
 649                 pr_debug("AMD CPPC shared memory based functionality is supported\n");
 650                 static_call_update(amd_pstate_enable, cppc_enable);
 651                 static_call_update(amd_pstate_init_perf, cppc_init_perf);
 652                 static_call_update(amd_pstate_update_perf, cppc_update_perf);
 653         }
 654
 655         /* enable amd pstate feature */
 656         ret = amd_pstate_enable(true);
 657         if (ret) {
 658                 pr_err("failed to enable amd-pstate with return %d\n", ret);
 659                 return ret;
 660         }
 661
 662         ret = cpufreq_register_driver(&amd_pstate_driver);
 663         if (ret)
 664                 pr_err("failed to register amd_pstate_driver with return %d\n",
 665                        ret);
 666
 667         return ret;
 668 }
 669 device_initcall(amd_pstate_init);
 670
 671 static int __init amd_pstate_param(char *str)
 672 {
 673         if (!str)
 674                 return -EINVAL;
 675
 676         if (!strcmp(str, "disable")) {
 677                 cppc_load = 0;
 678                 pr_info("driver is explicitly disabled\n");
 679         } else if (!strcmp(str, "passive"))
 680                 cppc_load = 1;
 681
 682         return 0;
 683 }
 684 early_param("amd_pstate", amd_pstate_param);
 685
 686 MODULE_AUTHOR("Huang Rui <ray.huang@amd.com>");
 687 MODULE_DESCRIPTION("AMD Processor P-state Frequency Driver");
 688 MODULE_LICENSE("GPL");