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