root/drivers/mailbox/pcc.c

DEFINITIONS

1. get_pcc_channel
2. read_register
3. write_register
4. pcc_map_interrupt
5. pcc_mbox_irq
6. pcc_mbox_request_channel
7. pcc_mbox_free_channel
8. pcc_send_data
9. parse_pcc_subspace
10. pcc_parse_subspace_irq
11. acpi_pcc_probe
12. pcc_mbox_probe
13. pcc_init

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /*
   3  *      Copyright (C) 2014 Linaro Ltd.
   4  *      Author: Ashwin Chaugule <ashwin.chaugule@linaro.org>
   5  *
   6  *  PCC (Platform Communication Channel) is defined in the ACPI 5.0+
   7  *  specification. It is a mailbox like mechanism to allow clients
   8  *  such as CPPC (Collaborative Processor Performance Control), RAS
   9  *  (Reliability, Availability and Serviceability) and MPST (Memory
  10  *  Node Power State Table) to talk to the platform (e.g. BMC) through
  11  *  shared memory regions as defined in the PCC table entries. The PCC
  12  *  specification supports a Doorbell mechanism for the PCC clients
  13  *  to notify the platform about new data. This Doorbell information
  14  *  is also specified in each PCC table entry.
  15  *
  16  *  Typical high level flow of operation is:
  17  *
  18  *  PCC Reads:
  19  *  * Client tries to acquire a channel lock.
  20  *  * After it is acquired it writes READ cmd in communication region cmd
  21  *              address.
  22  *  * Client issues mbox_send_message() which rings the PCC doorbell
  23  *              for its PCC channel.
  24  *  * If command completes, then client has control over channel and
  25  *              it can proceed with its reads.
  26  *  * Client releases lock.
  27  *
  28  *  PCC Writes:
  29  *  * Client tries to acquire channel lock.
  30  *  * Client writes to its communication region after it acquires a
  31  *              channel lock.
  32  *  * Client writes WRITE cmd in communication region cmd address.
  33  *  * Client issues mbox_send_message() which rings the PCC doorbell
  34  *              for its PCC channel.
  35  *  * If command completes, then writes have succeded and it can release
  36  *              the channel lock.
  37  *
  38  *  There is a Nominal latency defined for each channel which indicates
  39  *  how long to wait until a command completes. If command is not complete
  40  *  the client needs to retry or assume failure.
  41  *
  42  *      For more details about PCC, please see the ACPI specification from
  43  *  http://www.uefi.org/ACPIv5.1 Section 14.
  44  *
  45  *  This file implements PCC as a Mailbox controller and allows for PCC
  46  *  clients to be implemented as its Mailbox Client Channels.
  47  */
  48 
  49 #include <linux/acpi.h>
  50 #include <linux/delay.h>
  51 #include <linux/io.h>
  52 #include <linux/init.h>
  53 #include <linux/interrupt.h>
  54 #include <linux/list.h>
  55 #include <linux/platform_device.h>
  56 #include <linux/mailbox_controller.h>
  57 #include <linux/mailbox_client.h>
  58 #include <linux/io-64-nonatomic-lo-hi.h>
  59 #include <acpi/pcc.h>
  60 
  61 #include "mailbox.h"
  62 
  63 #define MBOX_IRQ_NAME           "pcc-mbox"
  64 
  65 static struct mbox_chan *pcc_mbox_channels;
  66 
  67 /* Array of cached virtual address for doorbell registers */
  68 static void __iomem **pcc_doorbell_vaddr;
  69 /* Array of cached virtual address for doorbell ack registers */
  70 static void __iomem **pcc_doorbell_ack_vaddr;
  71 /* Array of doorbell interrupts */
  72 static int *pcc_doorbell_irq;
  73 
  74 static struct mbox_controller pcc_mbox_ctrl = {};
  75 /**
  76  * get_pcc_channel - Given a PCC subspace idx, get
  77  *      the respective mbox_channel.
  78  * @id: PCC subspace index.
  79  *
  80  * Return: ERR_PTR(errno) if error, else pointer
  81  *      to mbox channel.
  82  */
  83 static struct mbox_chan *get_pcc_channel(int id)
  84 {
  85         if (id < 0 || id >= pcc_mbox_ctrl.num_chans)
  86                 return ERR_PTR(-ENOENT);
  87 
  88         return &pcc_mbox_channels[id];
  89 }
  90 
  91 /*
  92  * PCC can be used with perf critical drivers such as CPPC
  93  * So it makes sense to locally cache the virtual address and
  94  * use it to read/write to PCC registers such as doorbell register
  95  *
  96  * The below read_register and write_registers are used to read and
  97  * write from perf critical registers such as PCC doorbell register
  98  */
  99 static int read_register(void __iomem *vaddr, u64 *val, unsigned int bit_width)
 100 {
 101         int ret_val = 0;
 102 
 103         switch (bit_width) {
 104         case 8:
 105                 *val = readb(vaddr);
 106                 break;
 107         case 16:
 108                 *val = readw(vaddr);
 109                 break;
 110         case 32:
 111                 *val = readl(vaddr);
 112                 break;
 113         case 64:
 114                 *val = readq(vaddr);
 115                 break;
 116         default:
 117                 pr_debug("Error: Cannot read register of %u bit width",
 118                         bit_width);
 119                 ret_val = -EFAULT;
 120                 break;
 121         }
 122         return ret_val;
 123 }
 124 
 125 static int write_register(void __iomem *vaddr, u64 val, unsigned int bit_width)
 126 {
 127         int ret_val = 0;
 128 
 129         switch (bit_width) {
 130         case 8:
 131                 writeb(val, vaddr);
 132                 break;
 133         case 16:
 134                 writew(val, vaddr);
 135                 break;
 136         case 32:
 137                 writel(val, vaddr);
 138                 break;
 139         case 64:
 140                 writeq(val, vaddr);
 141                 break;
 142         default:
 143                 pr_debug("Error: Cannot write register of %u bit width",
 144                         bit_width);
 145                 ret_val = -EFAULT;
 146                 break;
 147         }
 148         return ret_val;
 149 }
 150 
 151 /**
 152  * pcc_map_interrupt - Map a PCC subspace GSI to a linux IRQ number
 153  * @interrupt: GSI number.
 154  * @flags: interrupt flags
 155  *
 156  * Returns: a valid linux IRQ number on success
 157  *              0 or -EINVAL on failure
 158  */
 159 static int pcc_map_interrupt(u32 interrupt, u32 flags)
 160 {
 161         int trigger, polarity;
 162 
 163         if (!interrupt)
 164                 return 0;
 165 
 166         trigger = (flags & ACPI_PCCT_INTERRUPT_MODE) ? ACPI_EDGE_SENSITIVE
 167                         : ACPI_LEVEL_SENSITIVE;
 168 
 169         polarity = (flags & ACPI_PCCT_INTERRUPT_POLARITY) ? ACPI_ACTIVE_LOW
 170                         : ACPI_ACTIVE_HIGH;
 171 
 172         return acpi_register_gsi(NULL, interrupt, trigger, polarity);
 173 }
 174 
 175 /**
 176  * pcc_mbox_irq - PCC mailbox interrupt handler
 177  */
 178 static irqreturn_t pcc_mbox_irq(int irq, void *p)
 179 {
 180         struct acpi_generic_address *doorbell_ack;
 181         struct acpi_pcct_hw_reduced *pcct_ss;
 182         struct mbox_chan *chan = p;
 183         u64 doorbell_ack_preserve;
 184         u64 doorbell_ack_write;
 185         u64 doorbell_ack_val;
 186         int ret;
 187 
 188         pcct_ss = chan->con_priv;
 189 
 190         mbox_chan_received_data(chan, NULL);
 191 
 192         if (pcct_ss->header.type == ACPI_PCCT_TYPE_HW_REDUCED_SUBSPACE_TYPE2) {
 193                 struct acpi_pcct_hw_reduced_type2 *pcct2_ss = chan->con_priv;
 194                 u32 id = chan - pcc_mbox_channels;
 195 
 196                 doorbell_ack = &pcct2_ss->platform_ack_register;
 197                 doorbell_ack_preserve = pcct2_ss->ack_preserve_mask;
 198                 doorbell_ack_write = pcct2_ss->ack_write_mask;
 199 
 200                 ret = read_register(pcc_doorbell_ack_vaddr[id],
 201                                     &doorbell_ack_val,
 202                                     doorbell_ack->bit_width);
 203                 if (ret)
 204                         return IRQ_NONE;
 205 
 206                 ret = write_register(pcc_doorbell_ack_vaddr[id],
 207                                      (doorbell_ack_val & doorbell_ack_preserve)
 208                                         | doorbell_ack_write,
 209                                      doorbell_ack->bit_width);
 210                 if (ret)
 211                         return IRQ_NONE;
 212         }
 213 
 214         return IRQ_HANDLED;
 215 }
 216 
 217 /**
 218  * pcc_mbox_request_channel - PCC clients call this function to
 219  *              request a pointer to their PCC subspace, from which they
 220  *              can get the details of communicating with the remote.
 221  * @cl: Pointer to Mailbox client, so we know where to bind the
 222  *              Channel.
 223  * @subspace_id: The PCC Subspace index as parsed in the PCC client
 224  *              ACPI package. This is used to lookup the array of PCC
 225  *              subspaces as parsed by the PCC Mailbox controller.
 226  *
 227  * Return: Pointer to the Mailbox Channel if successful or
 228  *              ERR_PTR.
 229  */
 230 struct mbox_chan *pcc_mbox_request_channel(struct mbox_client *cl,
 231                 int subspace_id)
 232 {
 233         struct device *dev = pcc_mbox_ctrl.dev;
 234         struct mbox_chan *chan;
 235         unsigned long flags;
 236 
 237         /*
 238          * Each PCC Subspace is a Mailbox Channel.
 239          * The PCC Clients get their PCC Subspace ID
 240          * from their own tables and pass it here.
 241          * This returns a pointer to the PCC subspace
 242          * for the Client to operate on.
 243          */
 244         chan = get_pcc_channel(subspace_id);
 245 
 246         if (IS_ERR(chan) || chan->cl) {
 247                 dev_err(dev, "Channel not found for idx: %d\n", subspace_id);
 248                 return ERR_PTR(-EBUSY);
 249         }
 250 
 251         spin_lock_irqsave(&chan->lock, flags);
 252         chan->msg_free = 0;
 253         chan->msg_count = 0;
 254         chan->active_req = NULL;
 255         chan->cl = cl;
 256         init_completion(&chan->tx_complete);
 257 
 258         if (chan->txdone_method == TXDONE_BY_POLL && cl->knows_txdone)
 259                 chan->txdone_method = TXDONE_BY_ACK;
 260 
 261         spin_unlock_irqrestore(&chan->lock, flags);
 262 
 263         if (pcc_doorbell_irq[subspace_id] > 0) {
 264                 int rc;
 265 
 266                 rc = devm_request_irq(dev, pcc_doorbell_irq[subspace_id],
 267                                       pcc_mbox_irq, 0, MBOX_IRQ_NAME, chan);
 268                 if (unlikely(rc)) {
 269                         dev_err(dev, "failed to register PCC interrupt %d\n",
 270                                 pcc_doorbell_irq[subspace_id]);
 271                         pcc_mbox_free_channel(chan);
 272                         chan = ERR_PTR(rc);
 273                 }
 274         }
 275 
 276         return chan;
 277 }
 278 EXPORT_SYMBOL_GPL(pcc_mbox_request_channel);
 279 
 280 /**
 281  * pcc_mbox_free_channel - Clients call this to free their Channel.
 282  *
 283  * @chan: Pointer to the mailbox channel as returned by
 284  *              pcc_mbox_request_channel()
 285  */
 286 void pcc_mbox_free_channel(struct mbox_chan *chan)
 287 {
 288         u32 id = chan - pcc_mbox_channels;
 289         unsigned long flags;
 290 
 291         if (!chan || !chan->cl)
 292                 return;
 293 
 294         if (id >= pcc_mbox_ctrl.num_chans) {
 295                 pr_debug("pcc_mbox_free_channel: Invalid mbox_chan passed\n");
 296                 return;
 297         }
 298 
 299         if (pcc_doorbell_irq[id] > 0)
 300                 devm_free_irq(chan->mbox->dev, pcc_doorbell_irq[id], chan);
 301 
 302         spin_lock_irqsave(&chan->lock, flags);
 303         chan->cl = NULL;
 304         chan->active_req = NULL;
 305         if (chan->txdone_method == TXDONE_BY_ACK)
 306                 chan->txdone_method = TXDONE_BY_POLL;
 307 
 308         spin_unlock_irqrestore(&chan->lock, flags);
 309 }
 310 EXPORT_SYMBOL_GPL(pcc_mbox_free_channel);
 311 
 312 /**
 313  * pcc_send_data - Called from Mailbox Controller code. Used
 314  *              here only to ring the channel doorbell. The PCC client
 315  *              specific read/write is done in the client driver in
 316  *              order to maintain atomicity over PCC channel once
 317  *              OS has control over it. See above for flow of operations.
 318  * @chan: Pointer to Mailbox channel over which to send data.
 319  * @data: Client specific data written over channel. Used here
 320  *              only for debug after PCC transaction completes.
 321  *
 322  * Return: Err if something failed else 0 for success.
 323  */
 324 static int pcc_send_data(struct mbox_chan *chan, void *data)
 325 {
 326         struct acpi_pcct_hw_reduced *pcct_ss = chan->con_priv;
 327         struct acpi_generic_address *doorbell;
 328         u64 doorbell_preserve;
 329         u64 doorbell_val;
 330         u64 doorbell_write;
 331         u32 id = chan - pcc_mbox_channels;
 332         int ret = 0;
 333 
 334         if (id >= pcc_mbox_ctrl.num_chans) {
 335                 pr_debug("pcc_send_data: Invalid mbox_chan passed\n");
 336                 return -ENOENT;
 337         }
 338 
 339         doorbell = &pcct_ss->doorbell_register;
 340         doorbell_preserve = pcct_ss->preserve_mask;
 341         doorbell_write = pcct_ss->write_mask;
 342 
 343         /* Sync notification from OS to Platform. */
 344         if (pcc_doorbell_vaddr[id]) {
 345                 ret = read_register(pcc_doorbell_vaddr[id], &doorbell_val,
 346                         doorbell->bit_width);
 347                 if (ret)
 348                         return ret;
 349                 ret = write_register(pcc_doorbell_vaddr[id],
 350                         (doorbell_val & doorbell_preserve) | doorbell_write,
 351                         doorbell->bit_width);
 352         } else {
 353                 ret = acpi_read(&doorbell_val, doorbell);
 354                 if (ret)
 355                         return ret;
 356                 ret = acpi_write((doorbell_val & doorbell_preserve) | doorbell_write,
 357                         doorbell);
 358         }
 359         return ret;
 360 }
 361 
 362 static const struct mbox_chan_ops pcc_chan_ops = {
 363         .send_data = pcc_send_data,
 364 };
 365 
 366 /**
 367  * parse_pcc_subspaces -- Count PCC subspaces defined
 368  * @header: Pointer to the ACPI subtable header under the PCCT.
 369  * @end: End of subtable entry.
 370  *
 371  * Return: If we find a PCC subspace entry of a valid type, return 0.
 372  *      Otherwise, return -EINVAL.
 373  *
 374  * This gets called for each entry in the PCC table.
 375  */
 376 static int parse_pcc_subspace(union acpi_subtable_headers *header,
 377                 const unsigned long end)
 378 {
 379         struct acpi_pcct_subspace *ss = (struct acpi_pcct_subspace *) header;
 380 
 381         if (ss->header.type < ACPI_PCCT_TYPE_RESERVED)
 382                 return 0;
 383 
 384         return -EINVAL;
 385 }
 386 
 387 /**
 388  * pcc_parse_subspace_irq - Parse the PCC IRQ and PCC ACK register
 389  *              There should be one entry per PCC client.
 390  * @id: PCC subspace index.
 391  * @pcct_ss: Pointer to the ACPI subtable header under the PCCT.
 392  *
 393  * Return: 0 for Success, else errno.
 394  *
 395  * This gets called for each entry in the PCC table.
 396  */
 397 static int pcc_parse_subspace_irq(int id,
 398                                   struct acpi_pcct_hw_reduced *pcct_ss)
 399 {
 400         pcc_doorbell_irq[id] = pcc_map_interrupt(pcct_ss->platform_interrupt,
 401                                                  (u32)pcct_ss->flags);
 402         if (pcc_doorbell_irq[id] <= 0) {
 403                 pr_err("PCC GSI %d not registered\n",
 404                        pcct_ss->platform_interrupt);
 405                 return -EINVAL;
 406         }
 407 
 408         if (pcct_ss->header.type
 409                 == ACPI_PCCT_TYPE_HW_REDUCED_SUBSPACE_TYPE2) {
 410                 struct acpi_pcct_hw_reduced_type2 *pcct2_ss = (void *)pcct_ss;
 411 
 412                 pcc_doorbell_ack_vaddr[id] = acpi_os_ioremap(
 413                                 pcct2_ss->platform_ack_register.address,
 414                                 pcct2_ss->platform_ack_register.bit_width / 8);
 415                 if (!pcc_doorbell_ack_vaddr[id]) {
 416                         pr_err("Failed to ioremap PCC ACK register\n");
 417                         return -ENOMEM;
 418                 }
 419         }
 420 
 421         return 0;
 422 }
 423 
 424 /**
 425  * acpi_pcc_probe - Parse the ACPI tree for the PCCT.
 426  *
 427  * Return: 0 for Success, else errno.
 428  */
 429 static int __init acpi_pcc_probe(void)
 430 {
 431         struct acpi_table_header *pcct_tbl;
 432         struct acpi_subtable_header *pcct_entry;
 433         struct acpi_table_pcct *acpi_pcct_tbl;
 434         struct acpi_subtable_proc proc[ACPI_PCCT_TYPE_RESERVED];
 435         int count, i, rc;
 436         acpi_status status = AE_OK;
 437 
 438         /* Search for PCCT */
 439         status = acpi_get_table(ACPI_SIG_PCCT, 0, &pcct_tbl);
 440 
 441         if (ACPI_FAILURE(status) || !pcct_tbl)
 442                 return -ENODEV;
 443 
 444         /* Set up the subtable handlers */
 445         for (i = ACPI_PCCT_TYPE_GENERIC_SUBSPACE;
 446              i < ACPI_PCCT_TYPE_RESERVED; i++) {
 447                 proc[i].id = i;
 448                 proc[i].count = 0;
 449                 proc[i].handler = parse_pcc_subspace;
 450         }
 451 
 452         count = acpi_table_parse_entries_array(ACPI_SIG_PCCT,
 453                         sizeof(struct acpi_table_pcct), proc,
 454                         ACPI_PCCT_TYPE_RESERVED, MAX_PCC_SUBSPACES);
 455         if (count <= 0 || count > MAX_PCC_SUBSPACES) {
 456                 if (count < 0)
 457                         pr_warn("Error parsing PCC subspaces from PCCT\n");
 458                 else
 459                         pr_warn("Invalid PCCT: %d PCC subspaces\n", count);
 460                 return -EINVAL;
 461         }
 462 
 463         pcc_mbox_channels = kcalloc(count, sizeof(struct mbox_chan),
 464                                     GFP_KERNEL);
 465         if (!pcc_mbox_channels) {
 466                 pr_err("Could not allocate space for PCC mbox channels\n");
 467                 return -ENOMEM;
 468         }
 469 
 470         pcc_doorbell_vaddr = kcalloc(count, sizeof(void *), GFP_KERNEL);
 471         if (!pcc_doorbell_vaddr) {
 472                 rc = -ENOMEM;
 473                 goto err_free_mbox;
 474         }
 475 
 476         pcc_doorbell_ack_vaddr = kcalloc(count, sizeof(void *), GFP_KERNEL);
 477         if (!pcc_doorbell_ack_vaddr) {
 478                 rc = -ENOMEM;
 479                 goto err_free_db_vaddr;
 480         }
 481 
 482         pcc_doorbell_irq = kcalloc(count, sizeof(int), GFP_KERNEL);
 483         if (!pcc_doorbell_irq) {
 484                 rc = -ENOMEM;
 485                 goto err_free_db_ack_vaddr;
 486         }
 487 
 488         /* Point to the first PCC subspace entry */
 489         pcct_entry = (struct acpi_subtable_header *) (
 490                 (unsigned long) pcct_tbl + sizeof(struct acpi_table_pcct));
 491 
 492         acpi_pcct_tbl = (struct acpi_table_pcct *) pcct_tbl;
 493         if (acpi_pcct_tbl->flags & ACPI_PCCT_DOORBELL)
 494                 pcc_mbox_ctrl.txdone_irq = true;
 495 
 496         for (i = 0; i < count; i++) {
 497                 struct acpi_generic_address *db_reg;
 498                 struct acpi_pcct_subspace *pcct_ss;
 499                 pcc_mbox_channels[i].con_priv = pcct_entry;
 500 
 501                 if (pcct_entry->type == ACPI_PCCT_TYPE_HW_REDUCED_SUBSPACE ||
 502                     pcct_entry->type == ACPI_PCCT_TYPE_HW_REDUCED_SUBSPACE_TYPE2) {
 503                         struct acpi_pcct_hw_reduced *pcct_hrss;
 504 
 505                         pcct_hrss = (struct acpi_pcct_hw_reduced *) pcct_entry;
 506 
 507                         if (pcc_mbox_ctrl.txdone_irq) {
 508                                 rc = pcc_parse_subspace_irq(i, pcct_hrss);
 509                                 if (rc < 0)
 510                                         goto err;
 511                         }
 512                 }
 513                 pcct_ss = (struct acpi_pcct_subspace *) pcct_entry;
 514 
 515                 /* If doorbell is in system memory cache the virt address */
 516                 db_reg = &pcct_ss->doorbell_register;
 517                 if (db_reg->space_id == ACPI_ADR_SPACE_SYSTEM_MEMORY)
 518                         pcc_doorbell_vaddr[i] = acpi_os_ioremap(db_reg->address,
 519                                                         db_reg->bit_width/8);
 520                 pcct_entry = (struct acpi_subtable_header *)
 521                         ((unsigned long) pcct_entry + pcct_entry->length);
 522         }
 523 
 524         pcc_mbox_ctrl.num_chans = count;
 525 
 526         pr_info("Detected %d PCC Subspaces\n", pcc_mbox_ctrl.num_chans);
 527 
 528         return 0;
 529 
 530 err:
 531         kfree(pcc_doorbell_irq);
 532 err_free_db_ack_vaddr:
 533         kfree(pcc_doorbell_ack_vaddr);
 534 err_free_db_vaddr:
 535         kfree(pcc_doorbell_vaddr);
 536 err_free_mbox:
 537         kfree(pcc_mbox_channels);
 538         return rc;
 539 }
 540 
 541 /**
 542  * pcc_mbox_probe - Called when we find a match for the
 543  *      PCCT platform device. This is purely used to represent
 544  *      the PCCT as a virtual device for registering with the
 545  *      generic Mailbox framework.
 546  *
 547  * @pdev: Pointer to platform device returned when a match
 548  *      is found.
 549  *
 550  *      Return: 0 for Success, else errno.
 551  */
 552 static int pcc_mbox_probe(struct platform_device *pdev)
 553 {
 554         int ret = 0;
 555 
 556         pcc_mbox_ctrl.chans = pcc_mbox_channels;
 557         pcc_mbox_ctrl.ops = &pcc_chan_ops;
 558         pcc_mbox_ctrl.dev = &pdev->dev;
 559 
 560         pr_info("Registering PCC driver as Mailbox controller\n");
 561         ret = mbox_controller_register(&pcc_mbox_ctrl);
 562 
 563         if (ret) {
 564                 pr_err("Err registering PCC as Mailbox controller: %d\n", ret);
 565                 ret = -ENODEV;
 566         }
 567 
 568         return ret;
 569 }
 570 
 571 struct platform_driver pcc_mbox_driver = {
 572         .probe = pcc_mbox_probe,
 573         .driver = {
 574                 .name = "PCCT",
 575                 .owner = THIS_MODULE,
 576         },
 577 };
 578 
 579 static int __init pcc_init(void)
 580 {
 581         int ret;
 582         struct platform_device *pcc_pdev;
 583 
 584         if (acpi_disabled)
 585                 return -ENODEV;
 586 
 587         /* Check if PCC support is available. */
 588         ret = acpi_pcc_probe();
 589 
 590         if (ret) {
 591                 pr_debug("ACPI PCC probe failed.\n");
 592                 return -ENODEV;
 593         }
 594 
 595         pcc_pdev = platform_create_bundle(&pcc_mbox_driver,
 596                         pcc_mbox_probe, NULL, 0, NULL, 0);
 597 
 598         if (IS_ERR(pcc_pdev)) {
 599                 pr_debug("Err creating PCC platform bundle\n");
 600                 return PTR_ERR(pcc_pdev);
 601         }
 602 
 603         return 0;
 604 }
 605 
 606 /*
 607  * Make PCC init postcore so that users of this mailbox
 608  * such as the ACPI Processor driver have it available
 609  * at their init.
 610  */
 611 postcore_initcall(pcc_init);