Linux音频设备驱动_OSS驱动框架（二）————OSS驱动架构代码vmsnd.c

在vmsnd驱动模块被加载时函数init_vwsnd()被调用，音频驱动被初始化，驱动初始化过程会查找硬件配置和匹配相应的驱动程序。函数init_vwsnd()的主要内容如下：

static int __init init_vwsnd(void)
{
    int err;

    DBGXV("\n");
    DBGXV("sound::vwsnd::init_module()\n");
    /*驱动的探测函数*/
    if (!probe_vwsnd(&the_hw_config))
        return -ENODEV;
    /*驱动附着函数*/
    err = attach_vwsnd(&the_hw_config);
    if (err < 0)
        return err;
    return 0;
}

在函数attach_vwsnd()中，调用了对数字音频设备的注册函数register_sound_dsp()和对混频器接口的注册函数register_sound_mixer()。函数的主要内容如下：

static int __init attach_vwsnd(struct address_info *hw_config)
{
    vwsnd_dev_t *devc = NULL;
    int err = -ENOMEM;

    DBGEV("(hw_config=0x%p)\n", hw_config);
    /*为devc分配空间*/
    devc = kmalloc(sizeof (vwsnd_dev_t), GFP_KERNEL);
    if (devc == NULL)
        goto fail0;
    /*下面是给结构体devc各个字段赋值*/
    err = li_create(&devc->lith, hw_config->io_base);
    if (err)
        goto fail1;

    init_waitqueue_head(&devc->open_wait);

    devc->rport.hwbuf_size = HWBUF_SIZE;
    devc->rport.hwbuf_vaddr = __get_free_pages(GFP_KERNEL, HWBUF_ORDER);
    if (!devc->rport.hwbuf_vaddr)
        goto fail2;
    devc->rport.hwbuf = (void *) devc->rport.hwbuf_vaddr;
    devc->rport.hwbuf_paddr = virt_to_phys(devc->rport.hwbuf);

     *
     * We set the input side's DMA base address here.  It will remain
     * valid until the driver is unloaded.
     */
    /*设置输入侧的DMA基地址，保持它到驱动被卸载前*/
    li_writel(&devc->lith, LI_COMM1_BASE,
          devc->rport.hwbuf_paddr >> 8 | 1 << (37 - 8));

    devc->wport.hwbuf_size = HWBUF_SIZE;
    devc->wport.hwbuf_vaddr = __get_free_pages(GFP_KERNEL, HWBUF_ORDER);
    if (!devc->wport.hwbuf_vaddr)
        goto fail3;
    devc->wport.hwbuf = (void *) devc->wport.hwbuf_vaddr;
    devc->wport.hwbuf_paddr = virt_to_phys(devc->wport.hwbuf);
    DBGP("wport hwbuf = 0x%p\n", devc->wport.hwbuf);

    DBGDO(shut_up++);
    err = ad1843_init(&devc->lith);
    DBGDO(shut_up--);
    if (err)
        goto fail4;

    /* install interrupt handler */

    err = request_irq(hw_config->irq, vwsnd_audio_intr, 0, "vwsnd", devc);
    if (err)
        goto fail5;

    /* register this device's drivers. */

    devc->audio_minor = register_sound_dsp(&vwsnd_audio_fops, -1);
    if ((err = devc->audio_minor) < 0) {
        DBGDO(printk(KERN_WARNING
                 "attach_vwsnd: register_sound_dsp error %d\n",
                 err));
        goto fail6;
    }
    devc->mixer_minor = register_sound_mixer(&vwsnd_mixer_fops,
                         devc->audio_minor >> 4);
    if ((err = devc->mixer_minor) < 0) {
        DBGDO(printk(KERN_WARNING
                 "attach_vwsnd: register_sound_mixer error %d\n",
                 err));
        goto fail7;
    }

    /* Squirrel away device indices for unload routine. */

    hw_config->slots[0] = devc->audio_minor;

    /* Initialize as much of *devc as possible */

    mutex_init(&devc->open_mutex);
    mutex_init(&devc->io_mutex);
    mutex_init(&devc->mix_mutex);
    devc->open_mode = 0;
    spin_lock_init(&devc->rport.lock);
    init_waitqueue_head(&devc->rport.queue);
    devc->rport.swstate = SW_OFF;
    devc->rport.hwstate = HW_STOPPED;
    devc->rport.flags = 0;
    devc->rport.swbuf = NULL;
    spin_lock_init(&devc->wport.lock);
    init_waitqueue_head(&devc->wport.queue);
    devc->wport.swstate = SW_OFF;
    devc->wport.hwstate = HW_STOPPED;
    devc->wport.flags = 0;
    devc->wport.swbuf = NULL;

    /* Success.  Link us onto the local device list. */

    devc->next_dev = vwsnd_dev_list;
    vwsnd_dev_list = devc;
    return devc->audio_minor;

    /* So many ways to fail.  Undo what we did. */

 fail7:
    unregister_sound_dsp(devc->audio_minor);
 fail6:
    free_irq(hw_config->irq, devc);
 fail5:
 fail4:
    free_pages(devc->wport.hwbuf_vaddr, HWBUF_ORDER);
 fail3:
    free_pages(devc->rport.hwbuf_vaddr, HWBUF_ORDER);
 fail2:
    li_destroy(&devc->lith);
 fail1:
    kfree(devc);
 fail0:
    return err;
}

OSS驱动程序在sound/oss目录下，核心代码文件为soundcard.c。该文件中定义了打开设备文件，读设备文件（录音），写设备文件（播放），关闭设备文件等功能。