alsa声卡分析alsa-utils调用过程（二）-tinymixer

继上一篇文章：http://www.cnblogs.com/linhaostudy/p/8515277.html

三、tinymixer调用分析：（tinymixer.log搜索节点：/dev/snd/controlCx）

还是一样，系统调用从应用层到kernel层，都要通过VFS来到file_operations；

我们使用tinymixer "SEC_MI2S_RX Audio Mixer MultiMedia1" 1打开通道看一下相应的流程；

log中的open("/dev/snd_controlCx")中对应的file_operations中：

 /*

  *  INIT PART

  */

 static const struct file_operations snd_ctl_f_ops =

 {

     .owner =    THIS_MODULE,

     .read =        snd_ctl_read,

     .open =        snd_ctl_open,

     .release =    snd_ctl_release,

     .llseek =    no_llseek,

     .poll =        snd_ctl_poll,

     .unlocked_ioctl =    snd_ctl_ioctl,

     .compat_ioctl =    snd_ctl_ioctl_compat,

     .fasync =    snd_ctl_fasync,

 };

tinymixer首先先调用open操作函数集；也就是snd_ctl_open打开control逻辑设备；

我们主要分析ioctl函数，由file_operations来到snd_ctl_ioctl函数中来：

 static long snd_ctl_ioctl(struct file *file, unsigned int cmd, unsigned long arg)

 {

     struct snd_ctl_file *ctl;

     struct snd_card *card;

     struct snd_kctl_ioctl *p;

     void __user *argp = (void __user *)arg;

     int __user *ip = argp;

     int err;

     ctl = file->private_data;

     card = ctl->card;

     if (snd_BUG_ON(!card))

         return -ENXIO;

     switch (cmd) {

     case SNDRV_CTL_IOCTL_PVERSION:

         return put_user(SNDRV_CTL_VERSION, ip) ? -EFAULT : ;

     case SNDRV_CTL_IOCTL_CARD_INFO:

         return snd_ctl_card_info(card, ctl, cmd, argp);

     case SNDRV_CTL_IOCTL_ELEM_LIST:

         return snd_ctl_elem_list(card, argp);

     case SNDRV_CTL_IOCTL_ELEM_INFO:

         return snd_ctl_elem_info_user(ctl, argp);

     case SNDRV_CTL_IOCTL_ELEM_READ:

         return snd_ctl_elem_read_user(card, argp);

     case SNDRV_CTL_IOCTL_ELEM_WRITE:

         return snd_ctl_elem_write_user(ctl, argp);

     case SNDRV_CTL_IOCTL_ELEM_LOCK:

         return snd_ctl_elem_lock(ctl, argp);

     case SNDRV_CTL_IOCTL_ELEM_UNLOCK:

         return snd_ctl_elem_unlock(ctl, argp);

     case SNDRV_CTL_IOCTL_ELEM_ADD:

         return snd_ctl_elem_add_user(ctl, argp, );

     case SNDRV_CTL_IOCTL_ELEM_REPLACE:

         return snd_ctl_elem_add_user(ctl, argp, );

     case SNDRV_CTL_IOCTL_ELEM_REMOVE:

         return snd_ctl_elem_remove(ctl, argp);

     case SNDRV_CTL_IOCTL_SUBSCRIBE_EVENTS:

         return snd_ctl_subscribe_events(ctl, ip);

     case SNDRV_CTL_IOCTL_TLV_READ:

         return snd_ctl_tlv_ioctl(ctl, argp, );

     case SNDRV_CTL_IOCTL_TLV_WRITE:

         return snd_ctl_tlv_ioctl(ctl, argp, );

     case SNDRV_CTL_IOCTL_TLV_COMMAND:

         return snd_ctl_tlv_ioctl(ctl, argp, -);

     case SNDRV_CTL_IOCTL_POWER:

         return -ENOPROTOOPT;

     case SNDRV_CTL_IOCTL_POWER_STATE:

 #ifdef CONFIG_PM

         return put_user(card->power_state, ip) ? -EFAULT : ;

 #else

         return put_user(SNDRV_CTL_POWER_D0, ip) ? -EFAULT : ;

 #endif

     }

     down_read(&snd_ioctl_rwsem);

     list_for_each_entry(p, &snd_control_ioctls, list) {

         err = p->fioctl(card, ctl, cmd, arg);

         if (err != -ENOIOCTLCMD) {

             up_read(&snd_ioctl_rwsem);

             return err;

         }

     }

     up_read(&snd_ioctl_rwsem);

     snd_printdd("unknown ioctl = 0x%x\n", cmd);

     return -ENOTTY;

 }

通过tinymixer.log搜索ioctl可以看到，进入：

 case SNDRV_CTL_IOCTL_ELEM_WRITE:

         return snd_ctl_elem_write_user(ctl, argp);

相应流程如下：

|->snd_ctl_ioctl

   |->snd_ctl_elem_write_user

     |->snd_ctl_elem_wirte

       |->kctl->put

          |=snd_soc_dapm_put_volsw

            |->snd_soc_dapm_mixer_update_power//找到使用这个kcontrol的path，根据该kcontrol的值来更新path的connect状态

               //更新path->connect状态

kcontrol、dapm widget、route/path创建与注册和它们之间的关系可以见：

ALSA声卡驱动的DAPM（一）-DPAM详解

ALSA声卡驱动的DAPM（二）-建立过程

巴特西

alsa声卡分析alsa-utils调用过程（二）-tinymixer

三、tinymixer调用分析：（tinymixer.log搜索节点：/dev/snd/controlCx）

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