Linux下SPI驅動分析(4)

接下來繼續看SPI主機註冊、刪除方法。

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    /* 又見神奇的分割線 */
 431/*-------------------------------------------------------------------------*/
 432
    /* SPI主機驅動刪除方法
     * 這裏是由設備驅動找到主機控制結構體，並釋放內存
     */
 433static void spi_master_release(struct device *dev)
 434{
 435        struct spi_master *master;
 436
 437        master = container_of(dev, struct spi_master, dev);
 438        kfree(master);
 439}
 440
    /* SPI主機設備類 */
 441static struct class spi_master_class = {
 442        .name           = "spi_master",
 443        .owner          = THIS_MODULE,
 444        .dev_release    = spi_master_release,
 445};
 446
 447
 448/**
 449 * spi_alloc_master - allocate SPI master controller
 450 * @dev: the controller, possibly using the platform_bus
 451 * @size: how much zeroed driver-private data to allocate; the pointer to this
 452 *      memory is in the driver_data field of the returned device,
 453 *      accessible with spi_master_get_devdata().
 454 * Context: can sleep
 455 *
 456 * This call is used only by SPI master controller drivers, which are the
 457 * only ones directly touching chip registers.  It's how they allocate
 458 * an spi_master structure, prior to calling spi_register_master().
 459 *
 460 * This must be called from context that can sleep.  It returns the SPI
 461 * master structure on success, else NULL.
 462 *
 463 * The caller is responsible for assigning the bus number and initializing
 464 * the master's methods before calling spi_register_master(); and (after errors
 465 * adding the device) calling spi_master_put() to prevent a memory leak.
 466 */
    /* 只用在直接操作芯片寄存器的SPI主機控制器驅動
     */
 467struct spi_master *spi_alloc_master(struct device *dev, unsigned size)
 468{
 469        struct spi_master       *master;
 470
 471        if (!dev)
 472                return NULL;
 473
            /* 多申請size用於存放設備私有數據 */
 474        master = kzalloc(size + sizeof *master, GFP_KERNEL);
 475        if (!master)
 476                return NULL;
 477
            /* 初始化設備，kobject、電源相關方法... */
 478        device_initialize(&master->dev);
            /* 設備類 */
 479        master->dev.class = &spi_master_class;
            /* 增加引用次數，並返回設備結構體 */
 480        master->dev.parent = get_device(dev);
            /* 設置設備私有數據 */
 481        spi_master_set_devdata(master, &master[1]);
 482
 483        return master;
 484}
 485EXPORT_SYMBOL_GPL(spi_alloc_master);
 486
 487/**
 488 * spi_register_master - register SPI master controller
 489 * @master: initialized master, originally from spi_alloc_master()
 490 * Context: can sleep
 491 *
 492 * SPI master controllers connect to their drivers using some non-SPI bus,
 493 * such as the platform bus.  The final stage of probe() in that code
 494 * includes calling spi_register_master() to hook up to this SPI bus glue.
 495 *
 496 * SPI controllers use board specific (often SOC specific) bus numbers,
 497 * and board-specific addressing for SPI devices combines those numbers
 498 * with chip select numbers.  Since SPI does not directly support dynamic
 499 * device identification, boards need configuration tables telling which
 500 * chip is at which address.
 501 *
 502 * This must be called from context that can sleep.  It returns zero on
 503 * success, else a negative error code (dropping the master's refcount).
 504 * After a successful return, the caller is responsible for calling
 505 * spi_unregister_master().
 506 */
 507int spi_register_master(struct spi_master *master)
 508{
 509        static atomic_t         dyn_bus_id = ATOMIC_INIT((1<<15) - 1);
 510        struct device           *dev = master->dev.parent;
 511        struct boardinfo        *bi;
 512        int                     status = -ENODEV;
 513        int                     dynamic = 0;
 514
 515        if (!dev)
 516                return -ENODEV;
 517
 518        /* even if it's just one always-selected device, there must
 519         * be at least one chipselect
 520         */
            /* 至少要有一個片選 */
 521        if (master->num_chipselect == 0)
 522                return -EINVAL;
 523
 524        /* convention:  dynamically assigned bus IDs count down from the max */
            /* 總線號從最大開始減 */
 525        if (master->bus_num < 0) {
 526                /* FIXME switch to an IDR based scheme, something like
 527                 * I2C now uses, so we can't run out of "dynamic" IDs
 528                 */
 529                master->bus_num = atomic_dec_return(&dyn_bus_id);
 530                dynamic = 1;
 531        }
 532
 533        spin_lock_init(&master->bus_lock_spinlock);
 534        mutex_init(&master->bus_lock_mutex);
            /* 指示SPI總線是否被鎖 */
 535        master->bus_lock_flag = 0;
 536
 537        /* register the device, then userspace will see it.
 538         * registration fails if the bus ID is in use.
 539         */
            /* 註冊設備，用戶空間就可以看到了
             * 失敗，當總線ID正在使用
             * 下面的設備添加與上一篇文章一樣 
             */
 540        dev_set_name(&master->dev, "spi%u", master->bus_num);
 541        status = device_add(&master->dev);
 542        if (status < 0)
 543                goto done;
 544        dev_dbg(dev, "registered master %s%s/n", dev_name(&master->dev),
 545                        dynamic ? " (dynamic)" : "");
 546
 547        mutex_lock(&board_lock);
            /* 添加主機設備鏈表 */
 548        list_add_tail(&master->list, &spi_master_list);
            /* 在主機鏈表中查找匹配板設備信息的添加設備 */
 549        list_for_each_entry(bi, &board_list, list)
 550                spi_match_master_to_boardinfo(master, &bi->board_info);
 551        mutex_unlock(&board_lock);
 552
 553        status = 0;
 554
 555        /* Register devices from the device tree */
            /* OF註冊SPI設備
             * 爲主節點的子節點中含有reg屬性的子節點註冊一個SPI設備
             */
 556        of_register_spi_devices(master);
 557done:
 558        return status;
 559}
 560EXPORT_SYMBOL_GPL(spi_register_master);
 561
 562
    /* 刪除設備驅動 */
 563static int __unregister(struct device *dev, void *null)
 564{
            /* 內聯函數，調用device_unregister
             * 從系統中刪除設備相關的電源方法、sysfs……釋放內存、刪除文件等
             * 減引用次數
             */
 565        spi_unregister_device(to_spi_device(dev));
 566        return 0;
 567}
 568
 569/**
 570 * spi_unregister_master - unregister SPI master controller
 571 * @master: the master being unregistered
 572 * Context: can sleep
 573 *
 574 * This call is used only by SPI master controller drivers, which are the
 575 * only ones directly touching chip registers.
 576 *
 577 * This must be called from context that can sleep.
 578 */
    /* 僅用在SPI主機控制驅動刪除 */
 579void spi_unregister_master(struct spi_master *master)
 580{
 581        int dummy;
 582
 583        mutex_lock(&board_lock);
            /* 刪除設備鏈表 */
 584        list_del(&master->list);
 585        mutex_unlock(&board_lock);
 586
            /* 刪除所有子設備 */
 587        dummy = device_for_each_child(&master->dev, NULL, __unregister);
            /* 刪除設備 */
 588        device_unregister(&master->dev);
 589}
 590EXPORT_SYMBOL_GPL(spi_unregister_master);
 591
 592static int __spi_master_match(struct device *dev, void *data)
 593{
 594        struct spi_master *m;
 595        u16 *bus_num = data;
 596
            /* 比較設備的總線數，一樣返回TRUE */
 597        m = container_of(dev, struct spi_master, dev);
 598        return m->bus_num == *bus_num;
 599}
 600
 601/**
 602 * spi_busnum_to_master - look up master associated with bus_num
 603 * @bus_num: the master's bus number
 604 * Context: can sleep
 605 *
 606 * This call may be used with devices that are registered after
 607 * arch init time.  It returns a refcounted pointer to the relevant
 608 * spi_master (which the caller must release), or NULL if there is
 609 * no such master registered.
 610 */
 611struct spi_master *spi_busnum_to_master(u16 bus_num)
 612{
 613        struct device           *dev;
 614        struct spi_master       *master = NULL;
 615
            /* 在主機設備類中查找與bus_num匹配的設備
             * 找到則返回主機設備結構體指針
             */
 616        dev = class_find_device(&spi_master_class, NULL, &bus_num,
 617                                __spi_master_match);
 618        if (dev)
 619                master = container_of(dev, struct spi_master, dev);
 620        /* reference got in class_find_device */
 621        return master;
 622}
 623EXPORT_SYMBOL_GPL(spi_busnum_to_master);

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接下來，看SPI的核心方法。

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