drivers/cpufreq/mediatek-cpufreq.c

   1 /*
   2  * Copyright (c) 2015 Linaro Ltd.
   3  * Author: Pi-Cheng Chen <pi-cheng.chen@linaro.org>
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License version 2 as
   7  * published by the Free Software Foundation.
   8  *
   9  * This program is distributed in the hope that it will be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  * GNU General Public License for more details.
  13  */
  14
  15 #include <linux/clk.h>
  16 #include <linux/cpu.h>
  17 #include <linux/cpu_cooling.h>
  18 #include <linux/cpufreq.h>
  19 #include <linux/cpumask.h>
  20 #include <linux/module.h>
  21 #include <linux/of.h>
  22 #include <linux/platform_device.h>
  23 #include <linux/pm_opp.h>
  24 #include <linux/regulator/consumer.h>
  25 #include <linux/slab.h>
  26 #include <linux/thermal.h>
  27
  28 #define MIN_VOLT_SHIFT          (100000)
  29 #define MAX_VOLT_SHIFT          (200000)
  30 #define MAX_VOLT_LIMIT          (1150000)
  31 #define VOLT_TOL                (10000)
  32
  33 /*
  34  * The struct mtk_cpu_dvfs_info holds necessary information for doing CPU DVFS
  35  * on each CPU power/clock domain of Mediatek SoCs. Each CPU cluster in
  36  * Mediatek SoCs has two voltage inputs, Vproc and Vsram. In some cases the two
  37  * voltage inputs need to be controlled under a hardware limitation:
  38  * 100mV < Vsram - Vproc < 200mV
  39  *
  40  * When scaling the clock frequency of a CPU clock domain, the clock source
  41  * needs to be switched to another stable PLL clock temporarily until
  42  * the original PLL becomes stable at target frequency.
  43  */
  44 struct mtk_cpu_dvfs_info {
  45         struct cpumask cpus;
  46         struct device *cpu_dev;
  47         struct regulator *proc_reg;
  48         struct regulator *sram_reg;
  49         struct clk *cpu_clk;
  50         struct clk *inter_clk;
  51         struct thermal_cooling_device *cdev;
  52         struct list_head list_head;
  53         int intermediate_voltage;
  54         bool need_voltage_tracking;
  55 };
  56
  57 static LIST_HEAD(dvfs_info_list);
  58
  59 static struct mtk_cpu_dvfs_info *mtk_cpu_dvfs_info_lookup(int cpu)
  60 {
  61         struct mtk_cpu_dvfs_info *info;
  62
  63         list_for_each_entry(info, &dvfs_info_list, list_head) {
  64                 if (cpumask_test_cpu(cpu, &info->cpus))
  65                         return info;
  66         }
  67
  68         return NULL;
  69 }
  70
  71 static int mtk_cpufreq_voltage_tracking(struct mtk_cpu_dvfs_info *info,
  72                                         int new_vproc)
  73 {
  74         struct regulator *proc_reg = info->proc_reg;
  75         struct regulator *sram_reg = info->sram_reg;
  76         int old_vproc, old_vsram, new_vsram, vsram, vproc, ret;
  77
  78         old_vproc = regulator_get_voltage(proc_reg);
  79         if (old_vproc < 0) {
  80                 pr_err("%s: invalid Vproc value: %d\n", __func__, old_vproc);
  81                 return old_vproc;
  82         }
  83         /* Vsram should not exceed the maximum allowed voltage of SoC. */
  84         new_vsram = min(new_vproc + MIN_VOLT_SHIFT, MAX_VOLT_LIMIT);
  85
  86         if (old_vproc < new_vproc) {
  87                 /*
  88                  * When scaling up voltages, Vsram and Vproc scale up step
  89                  * by step. At each step, set Vsram to (Vproc + 200mV) first,
  90                  * then set Vproc to (Vsram - 100mV).
  91                  * Keep doing it until Vsram and Vproc hit target voltages.
  92                  */
  93                 do {
  94                         old_vsram = regulator_get_voltage(sram_reg);
  95                         if (old_vsram < 0) {
  96                                 pr_err("%s: invalid Vsram value: %d\n",
  97                                        __func__, old_vsram);
  98                                 return old_vsram;
  99                         }
 100                         old_vproc = regulator_get_voltage(proc_reg);
 101                         if (old_vproc < 0) {
 102                                 pr_err("%s: invalid Vproc value: %d\n",
 103                                        __func__, old_vproc);
 104                                 return old_vproc;
 105                         }
 106
 107                         vsram = min(new_vsram, old_vproc + MAX_VOLT_SHIFT);
 108
 109                         if (vsram + VOLT_TOL >= MAX_VOLT_LIMIT) {
 110                                 vsram = MAX_VOLT_LIMIT;
 111
 112                                 /*
 113                                  * If the target Vsram hits the maximum voltage,
 114                                  * try to set the exact voltage value first.
 115                                  */
 116                                 ret = regulator_set_voltage(sram_reg, vsram,
 117                                                             vsram);
 118                                 if (ret)
 119                                         ret = regulator_set_voltage(sram_reg,
 120                                                         vsram - VOLT_TOL,
 121                                                         vsram);
 122
 123                                 vproc = new_vproc;
 124                         } else {
 125                                 ret = regulator_set_voltage(sram_reg, vsram,
 126                                                             vsram + VOLT_TOL);
 127
 128                                 vproc = vsram - MIN_VOLT_SHIFT;
 129                         }
 130                         if (ret)
 131                                 return ret;
 132
 133                         ret = regulator_set_voltage(proc_reg, vproc,
 134                                                     vproc + VOLT_TOL);
 135                         if (ret) {
 136                                 regulator_set_voltage(sram_reg, old_vsram,
 137                                                       old_vsram);
 138                                 return ret;
 139                         }
 140                 } while (vproc < new_vproc || vsram < new_vsram);
 141         } else if (old_vproc > new_vproc) {
 142                 /*
 143                  * When scaling down voltages, Vsram and Vproc scale down step
 144                  * by step. At each step, set Vproc to (Vsram - 200mV) first,
 145                  * then set Vproc to (Vproc + 100mV).
 146                  * Keep doing it until Vsram and Vproc hit target voltages.
 147                  */
 148                 do {
 149                         old_vproc = regulator_get_voltage(proc_reg);
 150                         if (old_vproc < 0) {
 151                                 pr_err("%s: invalid Vproc value: %d\n",
 152                                        __func__, old_vproc);
 153                                 return old_vproc;
 154                         }
 155                         old_vsram = regulator_get_voltage(sram_reg);
 156                         if (old_vsram < 0) {
 157                                 pr_err("%s: invalid Vsram value: %d\n",
 158                                        __func__, old_vsram);
 159                                 return old_vsram;
 160                         }
 161
 162                         vproc = max(new_vproc, old_vsram - MAX_VOLT_SHIFT);
 163                         ret = regulator_set_voltage(proc_reg, vproc,
 164                                                     vproc + VOLT_TOL);
 165                         if (ret)
 166                                 return ret;
 167
 168                         if (vproc == new_vproc)
 169                                 vsram = new_vsram;
 170                         else
 171                                 vsram = max(new_vsram, vproc + MIN_VOLT_SHIFT);
 172
 173                         if (vsram + VOLT_TOL >= MAX_VOLT_LIMIT) {
 174                                 vsram = MAX_VOLT_LIMIT;
 175
 176                                 /*
 177                                  * If the target Vsram hits the maximum voltage,
 178                                  * try to set the exact voltage value first.
 179                                  */
 180                                 ret = regulator_set_voltage(sram_reg, vsram,
 181                                                             vsram);
 182                                 if (ret)
 183                                         ret = regulator_set_voltage(sram_reg,
 184                                                         vsram - VOLT_TOL,
 185                                                         vsram);
 186                         } else {
 187                                 ret = regulator_set_voltage(sram_reg, vsram,
 188                                                             vsram + VOLT_TOL);
 189                         }
 190
 191                         if (ret) {
 192                                 regulator_set_voltage(proc_reg, old_vproc,
 193                                                       old_vproc);
 194                                 return ret;
 195                         }
 196                 } while (vproc > new_vproc + VOLT_TOL ||
 197                          vsram > new_vsram + VOLT_TOL);
 198         }
 199
 200         return 0;
 201 }
 202
 203 static int mtk_cpufreq_set_voltage(struct mtk_cpu_dvfs_info *info, int vproc)
 204 {
 205         if (info->need_voltage_tracking)
 206                 return mtk_cpufreq_voltage_tracking(info, vproc);
 207         else
 208                 return regulator_set_voltage(info->proc_reg, vproc,
 209                                              vproc + VOLT_TOL);
 210 }
 211
 212 static int mtk_cpufreq_set_target(struct cpufreq_policy *policy,
 213                                   unsigned int index)
 214 {
 215         struct cpufreq_frequency_table *freq_table = policy->freq_table;
 216         struct clk *cpu_clk = policy->clk;
 217         struct clk *armpll = clk_get_parent(cpu_clk);
 218         struct mtk_cpu_dvfs_info *info = policy->driver_data;
 219         struct device *cpu_dev = info->cpu_dev;
 220         struct dev_pm_opp *opp;
 221         long freq_hz, old_freq_hz;
 222         int vproc, old_vproc, inter_vproc, target_vproc, ret;
 223
 224         inter_vproc = info->intermediate_voltage;
 225
 226         old_freq_hz = clk_get_rate(cpu_clk);
 227         old_vproc = regulator_get_voltage(info->proc_reg);
 228         if (old_vproc < 0) {
 229                 pr_err("%s: invalid Vproc value: %d\n", __func__, old_vproc);
 230                 return old_vproc;
 231         }
 232
 233         freq_hz = freq_table[index].frequency * 1000;
 234
 235         opp = dev_pm_opp_find_freq_ceil(cpu_dev, &freq_hz);
 236         if (IS_ERR(opp)) {
 237                 pr_err("cpu%d: failed to find OPP for %ld\n",
 238                        policy->cpu, freq_hz);
 239                 return PTR_ERR(opp);
 240         }
 241         vproc = dev_pm_opp_get_voltage(opp);
 242         dev_pm_opp_put(opp);
 243
 244         /*
 245          * If the new voltage or the intermediate voltage is higher than the
 246          * current voltage, scale up voltage first.
 247          */
 248         target_vproc = (inter_vproc > vproc) ? inter_vproc : vproc;
 249         if (old_vproc < target_vproc) {
 250                 ret = mtk_cpufreq_set_voltage(info, target_vproc);
 251                 if (ret) {
 252                         pr_err("cpu%d: failed to scale up voltage!\n",
 253                                policy->cpu);
 254                         mtk_cpufreq_set_voltage(info, old_vproc);
 255                         return ret;
 256                 }
 257         }
 258
 259         /* Reparent the CPU clock to intermediate clock. */
 260         ret = clk_set_parent(cpu_clk, info->inter_clk);
 261         if (ret) {
 262                 pr_err("cpu%d: failed to re-parent cpu clock!\n",
 263                        policy->cpu);
 264                 mtk_cpufreq_set_voltage(info, old_vproc);
 265                 WARN_ON(1);
 266                 return ret;
 267         }
 268
 269         /* Set the original PLL to target rate. */
 270         ret = clk_set_rate(armpll, freq_hz);
 271         if (ret) {
 272                 pr_err("cpu%d: failed to scale cpu clock rate!\n",
 273                        policy->cpu);
 274                 clk_set_parent(cpu_clk, armpll);
 275                 mtk_cpufreq_set_voltage(info, old_vproc);
 276                 return ret;
 277         }
 278
 279         /* Set parent of CPU clock back to the original PLL. */
 280         ret = clk_set_parent(cpu_clk, armpll);
 281         if (ret) {
 282                 pr_err("cpu%d: failed to re-parent cpu clock!\n",
 283                        policy->cpu);
 284                 mtk_cpufreq_set_voltage(info, inter_vproc);
 285                 WARN_ON(1);
 286                 return ret;
 287         }
 288
 289         /*
 290          * If the new voltage is lower than the intermediate voltage or the
 291          * original voltage, scale down to the new voltage.
 292          */
 293         if (vproc < inter_vproc || vproc < old_vproc) {
 294                 ret = mtk_cpufreq_set_voltage(info, vproc);
 295                 if (ret) {
 296                         pr_err("cpu%d: failed to scale down voltage!\n",
 297                                policy->cpu);
 298                         clk_set_parent(cpu_clk, info->inter_clk);
 299                         clk_set_rate(armpll, old_freq_hz);
 300                         clk_set_parent(cpu_clk, armpll);
 301                         return ret;
 302                 }
 303         }
 304
 305         return 0;
 306 }
 307
 308 #define DYNAMIC_POWER "dynamic-power-coefficient"
 309
 310 static void mtk_cpufreq_ready(struct cpufreq_policy *policy)
 311 {
 312         struct mtk_cpu_dvfs_info *info = policy->driver_data;
 313         struct device_node *np = of_node_get(info->cpu_dev->of_node);
 314         u32 capacitance = 0;
 315
 316         if (WARN_ON(!np))
 317                 return;
 318
 319         if (of_find_property(np, "#cooling-cells", NULL)) {
 320                 of_property_read_u32(np, DYNAMIC_POWER, &capacitance);
 321
 322                 info->cdev = of_cpufreq_power_cooling_register(np,
 323                                                 policy, capacitance, NULL);
 324
 325                 if (IS_ERR(info->cdev)) {
 326                         dev_err(info->cpu_dev,
 327                                 "running cpufreq without cooling device: %ld\n",
 328                                 PTR_ERR(info->cdev));
 329
 330                         info->cdev = NULL;
 331                 }
 332         }
 333
 334         of_node_put(np);
 335 }
 336
 337 static int mtk_cpu_dvfs_info_init(struct mtk_cpu_dvfs_info *info, int cpu)
 338 {
 339         struct device *cpu_dev;
 340         struct regulator *proc_reg = ERR_PTR(-ENODEV);
 341         struct regulator *sram_reg = ERR_PTR(-ENODEV);
 342         struct clk *cpu_clk = ERR_PTR(-ENODEV);
 343         struct clk *inter_clk = ERR_PTR(-ENODEV);
 344         struct dev_pm_opp *opp;
 345         unsigned long rate;
 346         int ret;
 347
 348         cpu_dev = get_cpu_device(cpu);
 349         if (!cpu_dev) {
 350                 pr_err("failed to get cpu%d device\n", cpu);
 351                 return -ENODEV;
 352         }
 353
 354         cpu_clk = clk_get(cpu_dev, "cpu");
 355         if (IS_ERR(cpu_clk)) {
 356                 if (PTR_ERR(cpu_clk) == -EPROBE_DEFER)
 357                         pr_warn("cpu clk for cpu%d not ready, retry.\n", cpu);
 358                 else
 359                         pr_err("failed to get cpu clk for cpu%d\n", cpu);
 360
 361                 ret = PTR_ERR(cpu_clk);
 362                 return ret;
 363         }
 364
 365         inter_clk = clk_get(cpu_dev, "intermediate");
 366         if (IS_ERR(inter_clk)) {
 367                 if (PTR_ERR(inter_clk) == -EPROBE_DEFER)
 368                         pr_warn("intermediate clk for cpu%d not ready, retry.\n",
 369                                 cpu);
 370                 else
 371                         pr_err("failed to get intermediate clk for cpu%d\n",
 372                                cpu);
 373
 374                 ret = PTR_ERR(inter_clk);
 375                 goto out_free_resources;
 376         }
 377
 378         proc_reg = regulator_get_exclusive(cpu_dev, "proc");
 379         if (IS_ERR(proc_reg)) {
 380                 if (PTR_ERR(proc_reg) == -EPROBE_DEFER)
 381                         pr_warn("proc regulator for cpu%d not ready, retry.\n",
 382                                 cpu);
 383                 else
 384                         pr_err("failed to get proc regulator for cpu%d\n",
 385                                cpu);
 386
 387                 ret = PTR_ERR(proc_reg);
 388                 goto out_free_resources;
 389         }
 390
 391         /* Both presence and absence of sram regulator are valid cases. */
 392         sram_reg = regulator_get_exclusive(cpu_dev, "sram");
 393
 394         /* Get OPP-sharing information from "operating-points-v2" bindings */
 395         ret = dev_pm_opp_of_get_sharing_cpus(cpu_dev, &info->cpus);
 396         if (ret) {
 397                 pr_err("failed to get OPP-sharing information for cpu%d\n",
 398                        cpu);
 399                 goto out_free_resources;
 400         }
 401
 402         ret = dev_pm_opp_of_cpumask_add_table(&info->cpus);
 403         if (ret) {
 404                 pr_warn("no OPP table for cpu%d\n", cpu);
 405                 goto out_free_resources;
 406         }
 407
 408         /* Search a safe voltage for intermediate frequency. */
 409         rate = clk_get_rate(inter_clk);
 410         opp = dev_pm_opp_find_freq_ceil(cpu_dev, &rate);
 411         if (IS_ERR(opp)) {
 412                 pr_err("failed to get intermediate opp for cpu%d\n", cpu);
 413                 ret = PTR_ERR(opp);
 414                 goto out_free_opp_table;
 415         }
 416         info->intermediate_voltage = dev_pm_opp_get_voltage(opp);
 417         dev_pm_opp_put(opp);
 418
 419         info->cpu_dev = cpu_dev;
 420         info->proc_reg = proc_reg;
 421         info->sram_reg = IS_ERR(sram_reg) ? NULL : sram_reg;
 422         info->cpu_clk = cpu_clk;
 423         info->inter_clk = inter_clk;
 424
 425         /*
 426          * If SRAM regulator is present, software "voltage tracking" is needed
 427          * for this CPU power domain.
 428          */
 429         info->need_voltage_tracking = !IS_ERR(sram_reg);
 430
 431         return 0;
 432
 433 out_free_opp_table:
 434         dev_pm_opp_of_cpumask_remove_table(&info->cpus);
 435
 436 out_free_resources:
 437         if (!IS_ERR(proc_reg))
 438                 regulator_put(proc_reg);
 439         if (!IS_ERR(sram_reg))
 440                 regulator_put(sram_reg);
 441         if (!IS_ERR(cpu_clk))
 442                 clk_put(cpu_clk);
 443         if (!IS_ERR(inter_clk))
 444                 clk_put(inter_clk);
 445
 446         return ret;
 447 }
 448
 449 static void mtk_cpu_dvfs_info_release(struct mtk_cpu_dvfs_info *info)
 450 {
 451         if (!IS_ERR(info->proc_reg))
 452                 regulator_put(info->proc_reg);
 453         if (!IS_ERR(info->sram_reg))
 454                 regulator_put(info->sram_reg);
 455         if (!IS_ERR(info->cpu_clk))
 456                 clk_put(info->cpu_clk);
 457         if (!IS_ERR(info->inter_clk))
 458                 clk_put(info->inter_clk);
 459
 460         dev_pm_opp_of_cpumask_remove_table(&info->cpus);
 461 }
 462
 463 static int mtk_cpufreq_init(struct cpufreq_policy *policy)
 464 {
 465         struct mtk_cpu_dvfs_info *info;
 466         struct cpufreq_frequency_table *freq_table;
 467         int ret;
 468
 469         info = mtk_cpu_dvfs_info_lookup(policy->cpu);
 470         if (!info) {
 471                 pr_err("dvfs info for cpu%d is not initialized.\n",
 472                        policy->cpu);
 473                 return -EINVAL;
 474         }
 475
 476         ret = dev_pm_opp_init_cpufreq_table(info->cpu_dev, &freq_table);
 477         if (ret) {
 478                 pr_err("failed to init cpufreq table for cpu%d: %d\n",
 479                        policy->cpu, ret);
 480                 return ret;
 481         }
 482
 483         ret = cpufreq_table_validate_and_show(policy, freq_table);
 484         if (ret) {
 485                 pr_err("%s: invalid frequency table: %d\n", __func__, ret);
 486                 goto out_free_cpufreq_table;
 487         }
 488
 489         cpumask_copy(policy->cpus, &info->cpus);
 490         policy->driver_data = info;
 491         policy->clk = info->cpu_clk;
 492
 493         return 0;
 494
 495 out_free_cpufreq_table:
 496         dev_pm_opp_free_cpufreq_table(info->cpu_dev, &freq_table);
 497         return ret;
 498 }
 499
 500 static int mtk_cpufreq_exit(struct cpufreq_policy *policy)
 501 {
 502         struct mtk_cpu_dvfs_info *info = policy->driver_data;
 503
 504         cpufreq_cooling_unregister(info->cdev);
 505         dev_pm_opp_free_cpufreq_table(info->cpu_dev, &policy->freq_table);
 506
 507         return 0;
 508 }
 509
 510 static struct cpufreq_driver mtk_cpufreq_driver = {
 511         .flags = CPUFREQ_STICKY | CPUFREQ_NEED_INITIAL_FREQ_CHECK |
 512                  CPUFREQ_HAVE_GOVERNOR_PER_POLICY,
 513         .verify = cpufreq_generic_frequency_table_verify,
 514         .target_index = mtk_cpufreq_set_target,
 515         .get = cpufreq_generic_get,
 516         .init = mtk_cpufreq_init,
 517         .exit = mtk_cpufreq_exit,
 518         .ready = mtk_cpufreq_ready,
 519         .name = "mtk-cpufreq",
 520         .attr = cpufreq_generic_attr,
 521 };
 522
 523 static int mtk_cpufreq_probe(struct platform_device *pdev)
 524 {
 525         struct mtk_cpu_dvfs_info *info, *tmp;
 526         int cpu, ret;
 527
 528         for_each_possible_cpu(cpu) {
 529                 info = mtk_cpu_dvfs_info_lookup(cpu);
 530                 if (info)
 531                         continue;
 532
 533                 info = devm_kzalloc(&pdev->dev, sizeof(*info), GFP_KERNEL);
 534                 if (!info) {
 535                         ret = -ENOMEM;
 536                         goto release_dvfs_info_list;
 537                 }
 538
 539                 ret = mtk_cpu_dvfs_info_init(info, cpu);
 540                 if (ret) {
 541                         dev_err(&pdev->dev,
 542                                 "failed to initialize dvfs info for cpu%d\n",
 543                                 cpu);
 544                         goto release_dvfs_info_list;
 545                 }
 546
 547                 list_add(&info->list_head, &dvfs_info_list);
 548         }
 549
 550         ret = cpufreq_register_driver(&mtk_cpufreq_driver);
 551         if (ret) {
 552                 dev_err(&pdev->dev, "failed to register mtk cpufreq driver\n");
 553                 goto release_dvfs_info_list;
 554         }
 555
 556         return 0;
 557
 558 release_dvfs_info_list:
 559         list_for_each_entry_safe(info, tmp, &dvfs_info_list, list_head) {
 560                 mtk_cpu_dvfs_info_release(info);
 561                 list_del(&info->list_head);
 562         }
 563
 564         return ret;
 565 }
 566
 567 static struct platform_driver mtk_cpufreq_platdrv = {
 568         .driver = {
 569                 .name   = "mtk-cpufreq",
 570         },
 571         .probe          = mtk_cpufreq_probe,
 572 };
 573
 574 /* List of machines supported by this driver */
 575 static const struct of_device_id mtk_cpufreq_machines[] __initconst = {
 576         { .compatible = "mediatek,mt2701", },
 577         { .compatible = "mediatek,mt7622", },
 578         { .compatible = "mediatek,mt7623", },
 579         { .compatible = "mediatek,mt817x", },
 580         { .compatible = "mediatek,mt8173", },
 581         { .compatible = "mediatek,mt8176", },
 582
 583         { }
 584 };
 585
 586 static int __init mtk_cpufreq_driver_init(void)
 587 {
 588         struct device_node *np;
 589         const struct of_device_id *match;
 590         struct platform_device *pdev;
 591         int err;
 592
 593         np = of_find_node_by_path("/");
 594         if (!np)
 595                 return -ENODEV;
 596
 597         match = of_match_node(mtk_cpufreq_machines, np);
 598         of_node_put(np);
 599         if (!match) {
 600                 pr_warn("Machine is not compatible with mtk-cpufreq\n");
 601                 return -ENODEV;
 602         }
 603
 604         err = platform_driver_register(&mtk_cpufreq_platdrv);
 605         if (err)
 606                 return err;
 607
 608         /*
 609          * Since there's no place to hold device registration code and no
 610          * device tree based way to match cpufreq driver yet, both the driver
 611          * and the device registration codes are put here to handle defer
 612          * probing.
 613          */
 614         pdev = platform_device_register_simple("mtk-cpufreq", -1, NULL, 0);
 615         if (IS_ERR(pdev)) {
 616                 pr_err("failed to register mtk-cpufreq platform device\n");
 617                 return PTR_ERR(pdev);
 618         }
 619
 620         return 0;
 621 }
 622 device_initcall(mtk_cpufreq_driver_init);
 623
 624 MODULE_DESCRIPTION("MediaTek CPUFreq driver");
 625 MODULE_AUTHOR("Pi-Cheng Chen <pi-cheng.chen@linaro.org>");
 626 MODULE_LICENSE("GPL v2");