drivers/xen/xen-acpi-processor.c

   1 /*
   2  * Copyright 2012 by Oracle Inc
   3  * Author: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
   4  *
   5  * This code borrows ideas from https://lkml.org/lkml/2011/11/30/249
   6  * so many thanks go to Kevin Tian <kevin.tian@intel.com>
   7  * and Yu Ke <ke.yu@intel.com>.
   8  *
   9  * This program is free software; you can redistribute it and/or modify it
  10  * under the terms and conditions of the GNU General Public License,
  11  * version 2, as published by the Free Software Foundation.
  12  *
  13  * This program is distributed in the hope it will be useful, but WITHOUT
  14  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  15  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
  16  * more details.
  17  *
  18  */
  19
  20 #include <linux/cpumask.h>
  21 #include <linux/cpufreq.h>
  22 #include <linux/freezer.h>
  23 #include <linux/kernel.h>
  24 #include <linux/kthread.h>
  25 #include <linux/init.h>
  26 #include <linux/module.h>
  27 #include <linux/types.h>
  28 #include <acpi/acpi_bus.h>
  29 #include <acpi/acpi_drivers.h>
  30 #include <acpi/processor.h>
  31
  32 #include <xen/interface/platform.h>
  33 #include <asm/xen/hypercall.h>
  34
  35 #define DRV_NAME "xen-acpi-processor: "
  36
  37 static int no_hypercall;
  38 MODULE_PARM_DESC(off, "Inhibit the hypercall.");
  39 module_param_named(off, no_hypercall, int, 0400);
  40
  41 /*
  42  * Note: Do not convert the acpi_id* below to cpumask_var_t or use cpumask_bit
  43  * - as those shrink to nr_cpu_bits (which is dependent on possible_cpu), which
  44  * can be less than what we want to put in. Instead use the 'nr_acpi_bits'
  45  * which is dynamically computed based on the MADT or x2APIC table.
  46  */
  47 static unsigned int nr_acpi_bits;
  48 /* Mutex to protect the acpi_ids_done - for CPU hotplug use. */
  49 static DEFINE_MUTEX(acpi_ids_mutex);
  50 /* Which ACPI ID we have processed from 'struct acpi_processor'. */
  51 static unsigned long *acpi_ids_done;
  52 /* Which ACPI ID exist in the SSDT/DSDT processor definitions. */
  53 static unsigned long __initdata *acpi_id_present;
  54 /* And if there is an _CST definition (or a PBLK) for the ACPI IDs */
  55 static unsigned long __initdata *acpi_id_cst_present;
  56
  57 static int push_cxx_to_hypervisor(struct acpi_processor *_pr)
  58 {
  59         struct xen_platform_op op = {
  60                 .cmd                    = XENPF_set_processor_pminfo,
  61                 .interface_version      = XENPF_INTERFACE_VERSION,
  62                 .u.set_pminfo.id        = _pr->acpi_id,
  63                 .u.set_pminfo.type      = XEN_PM_CX,
  64         };
  65         struct xen_processor_cx *dst_cx, *dst_cx_states = NULL;
  66         struct acpi_processor_cx *cx;
  67         unsigned int i, ok;
  68         int ret = 0;
  69
  70         dst_cx_states = kcalloc(_pr->power.count,
  71                                 sizeof(struct xen_processor_cx), GFP_KERNEL);
  72         if (!dst_cx_states)
  73                 return -ENOMEM;
  74
  75         for (ok = 0, i = 1; i <= _pr->power.count; i++) {
  76                 cx = &_pr->power.states[i];
  77                 if (!cx->valid)
  78                         continue;
  79
  80                 dst_cx = &(dst_cx_states[ok++]);
  81
  82                 dst_cx->reg.space_id = ACPI_ADR_SPACE_SYSTEM_IO;
  83                 if (cx->entry_method == ACPI_CSTATE_SYSTEMIO) {
  84                         dst_cx->reg.bit_width = 8;
  85                         dst_cx->reg.bit_offset = 0;
  86                         dst_cx->reg.access_size = 1;
  87                 } else {
  88                         dst_cx->reg.space_id = ACPI_ADR_SPACE_FIXED_HARDWARE;
  89                         if (cx->entry_method == ACPI_CSTATE_FFH) {
  90                                 /* NATIVE_CSTATE_BEYOND_HALT */
  91                                 dst_cx->reg.bit_offset = 2;
  92                                 dst_cx->reg.bit_width = 1; /* VENDOR_INTEL */
  93                         }
  94                         dst_cx->reg.access_size = 0;
  95                 }
  96                 dst_cx->reg.address = cx->address;
  97
  98                 dst_cx->type = cx->type;
  99                 dst_cx->latency = cx->latency;
 100                 dst_cx->power = cx->power;
 101
 102                 dst_cx->dpcnt = 0;
 103                 set_xen_guest_handle(dst_cx->dp, NULL);
 104         }
 105         if (!ok) {
 106                 pr_debug(DRV_NAME "No _Cx for ACPI CPU %u\n", _pr->acpi_id);
 107                 kfree(dst_cx_states);
 108                 return -EINVAL;
 109         }
 110         op.u.set_pminfo.power.count = ok;
 111         op.u.set_pminfo.power.flags.bm_control = _pr->flags.bm_control;
 112         op.u.set_pminfo.power.flags.bm_check = _pr->flags.bm_check;
 113         op.u.set_pminfo.power.flags.has_cst = _pr->flags.has_cst;
 114         op.u.set_pminfo.power.flags.power_setup_done =
 115                 _pr->flags.power_setup_done;
 116
 117         set_xen_guest_handle(op.u.set_pminfo.power.states, dst_cx_states);
 118
 119         if (!no_hypercall)
 120                 ret = HYPERVISOR_dom0_op(&op);
 121
 122         if (!ret) {
 123                 pr_debug("ACPI CPU%u - C-states uploaded.\n", _pr->acpi_id);
 124                 for (i = 1; i <= _pr->power.count; i++) {
 125                         cx = &_pr->power.states[i];
 126                         if (!cx->valid)
 127                                 continue;
 128                         pr_debug("     C%d: %s %d uS\n",
 129                                  cx->type, cx->desc, (u32)cx->latency);
 130                 }
 131         } else
 132                 pr_err(DRV_NAME "(CX): Hypervisor error (%d) for ACPI CPU%u\n",
 133                        ret, _pr->acpi_id);
 134
 135         kfree(dst_cx_states);
 136
 137         return ret;
 138 }
 139 static struct xen_processor_px *
 140 xen_copy_pss_data(struct acpi_processor *_pr,
 141                   struct xen_processor_performance *dst_perf)
 142 {
 143         struct xen_processor_px *dst_states = NULL;
 144         unsigned int i;
 145
 146         BUILD_BUG_ON(sizeof(struct xen_processor_px) !=
 147                      sizeof(struct acpi_processor_px));
 148
 149         dst_states = kcalloc(_pr->performance->state_count,
 150                              sizeof(struct xen_processor_px), GFP_KERNEL);
 151         if (!dst_states)
 152                 return ERR_PTR(-ENOMEM);
 153
 154         dst_perf->state_count = _pr->performance->state_count;
 155         for (i = 0; i < _pr->performance->state_count; i++) {
 156                 /* Fortunatly for us, they are both the same size */
 157                 memcpy(&(dst_states[i]), &(_pr->performance->states[i]),
 158                        sizeof(struct acpi_processor_px));
 159         }
 160         return dst_states;
 161 }
 162 static int xen_copy_psd_data(struct acpi_processor *_pr,
 163                              struct xen_processor_performance *dst)
 164 {
 165         struct acpi_psd_package *pdomain;
 166
 167         BUILD_BUG_ON(sizeof(struct xen_psd_package) !=
 168                      sizeof(struct acpi_psd_package));
 169
 170         /* This information is enumerated only if acpi_processor_preregister_performance
 171          * has been called.
 172          */
 173         dst->shared_type = _pr->performance->shared_type;
 174
 175         pdomain = &(_pr->performance->domain_info);
 176
 177         /* 'acpi_processor_preregister_performance' does not parse if the
 178          * num_processors <= 1, but Xen still requires it. Do it manually here.
 179          */
 180         if (pdomain->num_processors <= 1) {
 181                 if (pdomain->coord_type == DOMAIN_COORD_TYPE_SW_ALL)
 182                         dst->shared_type = CPUFREQ_SHARED_TYPE_ALL;
 183                 else if (pdomain->coord_type == DOMAIN_COORD_TYPE_HW_ALL)
 184                         dst->shared_type = CPUFREQ_SHARED_TYPE_HW;
 185                 else if (pdomain->coord_type == DOMAIN_COORD_TYPE_SW_ANY)
 186                         dst->shared_type = CPUFREQ_SHARED_TYPE_ANY;
 187
 188         }
 189         memcpy(&(dst->domain_info), pdomain, sizeof(struct acpi_psd_package));
 190         return 0;
 191 }
 192 static int xen_copy_pct_data(struct acpi_pct_register *pct,
 193                              struct xen_pct_register *dst_pct)
 194 {
 195         /* It would be nice if you could just do 'memcpy(pct, dst_pct') but
 196          * sadly the Xen structure did not have the proper padding so the
 197          * descriptor field takes two (dst_pct) bytes instead of one (pct).
 198          */
 199         dst_pct->descriptor = pct->descriptor;
 200         dst_pct->length = pct->length;
 201         dst_pct->space_id = pct->space_id;
 202         dst_pct->bit_width = pct->bit_width;
 203         dst_pct->bit_offset = pct->bit_offset;
 204         dst_pct->reserved = pct->reserved;
 205         dst_pct->address = pct->address;
 206         return 0;
 207 }
 208 static int push_pxx_to_hypervisor(struct acpi_processor *_pr)
 209 {
 210         int ret = 0;
 211         struct xen_platform_op op = {
 212                 .cmd                    = XENPF_set_processor_pminfo,
 213                 .interface_version      = XENPF_INTERFACE_VERSION,
 214                 .u.set_pminfo.id        = _pr->acpi_id,
 215                 .u.set_pminfo.type      = XEN_PM_PX,
 216         };
 217         struct xen_processor_performance *dst_perf;
 218         struct xen_processor_px *dst_states = NULL;
 219
 220         dst_perf = &op.u.set_pminfo.perf;
 221
 222         dst_perf->platform_limit = _pr->performance_platform_limit;
 223         dst_perf->flags |= XEN_PX_PPC;
 224         xen_copy_pct_data(&(_pr->performance->control_register),
 225                           &dst_perf->control_register);
 226         xen_copy_pct_data(&(_pr->performance->status_register),
 227                           &dst_perf->status_register);
 228         dst_perf->flags |= XEN_PX_PCT;
 229         dst_states = xen_copy_pss_data(_pr, dst_perf);
 230         if (!IS_ERR_OR_NULL(dst_states)) {
 231                 set_xen_guest_handle(dst_perf->states, dst_states);
 232                 dst_perf->flags |= XEN_PX_PSS;
 233         }
 234         if (!xen_copy_psd_data(_pr, dst_perf))
 235                 dst_perf->flags |= XEN_PX_PSD;
 236
 237         if (dst_perf->flags != (XEN_PX_PSD | XEN_PX_PSS | XEN_PX_PCT | XEN_PX_PPC)) {
 238                 pr_warn(DRV_NAME "ACPI CPU%u missing some P-state data (%x), skipping.\n",
 239                         _pr->acpi_id, dst_perf->flags);
 240                 ret = -ENODEV;
 241                 goto err_free;
 242         }
 243
 244         if (!no_hypercall)
 245                 ret = HYPERVISOR_dom0_op(&op);
 246
 247         if (!ret) {
 248                 struct acpi_processor_performance *perf;
 249                 unsigned int i;
 250
 251                 perf = _pr->performance;
 252                 pr_debug("ACPI CPU%u - P-states uploaded.\n", _pr->acpi_id);
 253                 for (i = 0; i < perf->state_count; i++) {
 254                         pr_debug("     %cP%d: %d MHz, %d mW, %d uS\n",
 255                         (i == perf->state ? '*' : ' '), i,
 256                         (u32) perf->states[i].core_frequency,
 257                         (u32) perf->states[i].power,
 258                         (u32) perf->states[i].transition_latency);
 259                 }
 260         } else if (ret != -EINVAL)
 261                 /* EINVAL means the ACPI ID is incorrect - meaning the ACPI
 262                  * table is referencing a non-existing CPU - which can happen
 263                  * with broken ACPI tables. */
 264                 pr_warn(DRV_NAME "(_PXX): Hypervisor error (%d) for ACPI CPU%u\n",
 265                        ret, _pr->acpi_id);
 266 err_free:
 267         if (!IS_ERR_OR_NULL(dst_states))
 268                 kfree(dst_states);
 269
 270         return ret;
 271 }
 272 static int upload_pm_data(struct acpi_processor *_pr)
 273 {
 274         int err = 0;
 275
 276         mutex_lock(&acpi_ids_mutex);
 277         if (__test_and_set_bit(_pr->acpi_id, acpi_ids_done)) {
 278                 mutex_unlock(&acpi_ids_mutex);
 279                 return -EBUSY;
 280         }
 281         if (_pr->flags.power)
 282                 err = push_cxx_to_hypervisor(_pr);
 283
 284         if (_pr->performance && _pr->performance->states)
 285                 err |= push_pxx_to_hypervisor(_pr);
 286
 287         mutex_unlock(&acpi_ids_mutex);
 288         return err;
 289 }
 290 static unsigned int __init get_max_acpi_id(void)
 291 {
 292         struct xenpf_pcpuinfo *info;
 293         struct xen_platform_op op = {
 294                 .cmd = XENPF_get_cpuinfo,
 295                 .interface_version = XENPF_INTERFACE_VERSION,
 296         };
 297         int ret = 0;
 298         unsigned int i, last_cpu, max_acpi_id = 0;
 299
 300         info = &op.u.pcpu_info;
 301         info->xen_cpuid = 0;
 302
 303         ret = HYPERVISOR_dom0_op(&op);
 304         if (ret)
 305                 return NR_CPUS;
 306
 307         /* The max_present is the same irregardless of the xen_cpuid */
 308         last_cpu = op.u.pcpu_info.max_present;
 309         for (i = 0; i <= last_cpu; i++) {
 310                 info->xen_cpuid = i;
 311                 ret = HYPERVISOR_dom0_op(&op);
 312                 if (ret)
 313                         continue;
 314                 max_acpi_id = max(info->acpi_id, max_acpi_id);
 315         }
 316         max_acpi_id *= 2; /* Slack for CPU hotplug support. */
 317         pr_debug(DRV_NAME "Max ACPI ID: %u\n", max_acpi_id);
 318         return max_acpi_id;
 319 }
 320 /*
 321  * The read_acpi_id and check_acpi_ids are there to support the Xen
 322  * oddity of virtual CPUs != physical CPUs in the initial domain.
 323  * The user can supply 'xen_max_vcpus=X' on the Xen hypervisor line
 324  * which will band the amount of CPUs the initial domain can see.
 325  * In general that is OK, except it plays havoc with any of the
 326  * for_each_[present|online]_cpu macros which are banded to the virtual
 327  * CPU amount.
 328  */
 329 static acpi_status __init
 330 read_acpi_id(acpi_handle handle, u32 lvl, void *context, void **rv)
 331 {
 332         u32 acpi_id;
 333         acpi_status status;
 334         acpi_object_type acpi_type;
 335         unsigned long long tmp;
 336         union acpi_object object = { 0 };
 337         struct acpi_buffer buffer = { sizeof(union acpi_object), &object };
 338         acpi_io_address pblk = 0;
 339
 340         status = acpi_get_type(handle, &acpi_type);
 341         if (ACPI_FAILURE(status))
 342                 return AE_OK;
 343
 344         switch (acpi_type) {
 345         case ACPI_TYPE_PROCESSOR:
 346                 status = acpi_evaluate_object(handle, NULL, NULL, &buffer);
 347                 if (ACPI_FAILURE(status))
 348                         return AE_OK;
 349                 acpi_id = object.processor.proc_id;
 350                 pblk = object.processor.pblk_address;
 351                 break;
 352         case ACPI_TYPE_DEVICE:
 353                 status = acpi_evaluate_integer(handle, "_UID", NULL, &tmp);
 354                 if (ACPI_FAILURE(status))
 355                         return AE_OK;
 356                 acpi_id = tmp;
 357                 break;
 358         default:
 359                 return AE_OK;
 360         }
 361         /* There are more ACPI Processor objects than in x2APIC or MADT.
 362          * This can happen with incorrect ACPI SSDT declerations. */
 363         if (acpi_id > nr_acpi_bits) {
 364                 pr_debug(DRV_NAME "We only have %u, trying to set %u\n",
 365                          nr_acpi_bits, acpi_id);
 366                 return AE_OK;
 367         }
 368         /* OK, There is a ACPI Processor object */
 369         __set_bit(acpi_id, acpi_id_present);
 370
 371         pr_debug(DRV_NAME "ACPI CPU%u w/ PBLK:0x%lx\n", acpi_id,
 372                  (unsigned long)pblk);
 373
 374         status = acpi_evaluate_object(handle, "_CST", NULL, &buffer);
 375         if (ACPI_FAILURE(status)) {
 376                 if (!pblk)
 377                         return AE_OK;
 378         }
 379         /* .. and it has a C-state */
 380         __set_bit(acpi_id, acpi_id_cst_present);
 381
 382         return AE_OK;
 383 }
 384 static int __init check_acpi_ids(struct acpi_processor *pr_backup)
 385 {
 386
 387         if (!pr_backup)
 388                 return -ENODEV;
 389
 390         /* All online CPUs have been processed at this stage. Now verify
 391          * whether in fact "online CPUs" == physical CPUs.
 392          */
 393         acpi_id_present = kcalloc(BITS_TO_LONGS(nr_acpi_bits), sizeof(unsigned long), GFP_KERNEL);
 394         if (!acpi_id_present)
 395                 return -ENOMEM;
 396
 397         acpi_id_cst_present = kcalloc(BITS_TO_LONGS(nr_acpi_bits), sizeof(unsigned long), GFP_KERNEL);
 398         if (!acpi_id_cst_present) {
 399                 kfree(acpi_id_present);
 400                 return -ENOMEM;
 401         }
 402
 403         acpi_walk_namespace(ACPI_TYPE_PROCESSOR, ACPI_ROOT_OBJECT,
 404                             ACPI_UINT32_MAX,
 405                             read_acpi_id, NULL, NULL, NULL);
 406         acpi_get_devices("ACPI0007", read_acpi_id, NULL, NULL);
 407
 408         if (!bitmap_equal(acpi_id_present, acpi_ids_done, nr_acpi_bits)) {
 409                 unsigned int i;
 410                 for_each_set_bit(i, acpi_id_present, nr_acpi_bits) {
 411                         pr_backup->acpi_id = i;
 412                         /* Mask out C-states if there are no _CST or PBLK */
 413                         pr_backup->flags.power = test_bit(i, acpi_id_cst_present);
 414                         (void)upload_pm_data(pr_backup);
 415                 }
 416         }
 417         kfree(acpi_id_present);
 418         acpi_id_present = NULL;
 419         kfree(acpi_id_cst_present);
 420         acpi_id_cst_present = NULL;
 421         return 0;
 422 }
 423 static int __init check_prereq(void)
 424 {
 425         struct cpuinfo_x86 *c = &cpu_data(0);
 426
 427         if (!xen_initial_domain())
 428                 return -ENODEV;
 429
 430         if (!acpi_gbl_FADT.smi_command)
 431                 return -ENODEV;
 432
 433         if (c->x86_vendor == X86_VENDOR_INTEL) {
 434                 if (!cpu_has(c, X86_FEATURE_EST))
 435                         return -ENODEV;
 436
 437                 return 0;
 438         }
 439         if (c->x86_vendor == X86_VENDOR_AMD) {
 440                 /* Copied from powernow-k8.h, can't include ../cpufreq/powernow
 441                  * as we get compile warnings for the static functions.
 442                  */
 443 #define CPUID_FREQ_VOLT_CAPABILITIES    0x80000007
 444 #define USE_HW_PSTATE                   0x00000080
 445                 u32 eax, ebx, ecx, edx;
 446                 cpuid(CPUID_FREQ_VOLT_CAPABILITIES, &eax, &ebx, &ecx, &edx);
 447                 if ((edx & USE_HW_PSTATE) != USE_HW_PSTATE)
 448                         return -ENODEV;
 449                 return 0;
 450         }
 451         return -ENODEV;
 452 }
 453 /* acpi_perf_data is a pointer to percpu data. */
 454 static struct acpi_processor_performance __percpu *acpi_perf_data;
 455
 456 static void free_acpi_perf_data(void)
 457 {
 458         unsigned int i;
 459
 460         /* Freeing a NULL pointer is OK, and alloc_percpu zeroes. */
 461         for_each_possible_cpu(i)
 462                 free_cpumask_var(per_cpu_ptr(acpi_perf_data, i)
 463                                  ->shared_cpu_map);
 464         free_percpu(acpi_perf_data);
 465 }
 466
 467 static int __init xen_acpi_processor_init(void)
 468 {
 469         struct acpi_processor *pr_backup = NULL;
 470         unsigned int i;
 471         int rc = check_prereq();
 472
 473         if (rc)
 474                 return rc;
 475
 476         nr_acpi_bits = get_max_acpi_id() + 1;
 477         acpi_ids_done = kcalloc(BITS_TO_LONGS(nr_acpi_bits), sizeof(unsigned long), GFP_KERNEL);
 478         if (!acpi_ids_done)
 479                 return -ENOMEM;
 480
 481         acpi_perf_data = alloc_percpu(struct acpi_processor_performance);
 482         if (!acpi_perf_data) {
 483                 pr_debug(DRV_NAME "Memory allocation error for acpi_perf_data.\n");
 484                 kfree(acpi_ids_done);
 485                 return -ENOMEM;
 486         }
 487         for_each_possible_cpu(i) {
 488                 if (!zalloc_cpumask_var_node(
 489                         &per_cpu_ptr(acpi_perf_data, i)->shared_cpu_map,
 490                         GFP_KERNEL, cpu_to_node(i))) {
 491                         rc = -ENOMEM;
 492                         goto err_out;
 493                 }
 494         }
 495
 496         /* Do initialization in ACPI core. It is OK to fail here. */
 497         (void)acpi_processor_preregister_performance(acpi_perf_data);
 498
 499         for_each_possible_cpu(i) {
 500                 struct acpi_processor_performance *perf;
 501
 502                 perf = per_cpu_ptr(acpi_perf_data, i);
 503                 rc = acpi_processor_register_performance(perf, i);
 504                 if (WARN_ON(rc))
 505                         goto err_out;
 506         }
 507         rc = acpi_processor_notify_smm(THIS_MODULE);
 508         if (WARN_ON(rc))
 509                 goto err_unregister;
 510
 511         for_each_possible_cpu(i) {
 512                 struct acpi_processor *_pr;
 513                 _pr = per_cpu(processors, i /* APIC ID */);
 514                 if (!_pr)
 515                         continue;
 516
 517                 if (!pr_backup) {
 518                         pr_backup = kzalloc(sizeof(struct acpi_processor), GFP_KERNEL);
 519                         memcpy(pr_backup, _pr, sizeof(struct acpi_processor));
 520                 }
 521                 (void)upload_pm_data(_pr);
 522         }
 523         rc = check_acpi_ids(pr_backup);
 524         if (rc)
 525                 goto err_unregister;
 526
 527         kfree(pr_backup);
 528
 529         return 0;
 530 err_unregister:
 531         for_each_possible_cpu(i) {
 532                 struct acpi_processor_performance *perf;
 533                 perf = per_cpu_ptr(acpi_perf_data, i);
 534                 acpi_processor_unregister_performance(perf, i);
 535         }
 536 err_out:
 537         /* Freeing a NULL pointer is OK: alloc_percpu zeroes. */
 538         free_acpi_perf_data();
 539         kfree(acpi_ids_done);
 540         return rc;
 541 }
 542 static void __exit xen_acpi_processor_exit(void)
 543 {
 544         int i;
 545
 546         kfree(acpi_ids_done);
 547         for_each_possible_cpu(i) {
 548                 struct acpi_processor_performance *perf;
 549                 perf = per_cpu_ptr(acpi_perf_data, i);
 550                 acpi_processor_unregister_performance(perf, i);
 551         }
 552         free_acpi_perf_data();
 553 }
 554
 555 MODULE_AUTHOR("Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>");
 556 MODULE_DESCRIPTION("Xen ACPI Processor P-states (and Cx) driver which uploads PM data to Xen hypervisor");
 557 MODULE_LICENSE("GPL");
 558
 559 /* We want to be loaded before the CPU freq scaling drivers are loaded.
 560  * They are loaded in late_initcall. */
 561 device_initcall(xen_acpi_processor_init);
 562 module_exit(xen_acpi_processor_exit);