一.ALSA核心层注册流程分析

驱动目录：kernel-4.9/sound/core/sound.c

struct file_operations snd_fops ={.owner = THIS_MODULE,.open = snd_open, (inode, file)---->struct snd_minor *mptr = snd_minors[minor];---->file->f_op = fops_get(mptr->f_ops);---->file->f_op->open(inode, file);.llseek = noop_llseek,}

1.alsa_sound_init()

---->register_chrdev(major, "alsa", &snd_fops)---->__register_chrdev(major, 0, 256, name, fops);

这里注册了256个cdev

驱动目录：kernel-4.9/sound/core/control.c

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,
};

snd_ctl_dev_register(struct snd_device *device)
---->sprintf(name, "controlC%i", cardnum);---->snd_register_device(SNDRV_DEVICE_TYPE_CONTROL, card, -1,&snd_ctl_f_ops, card, name)) < 0)

驱动目录：

kernel-4.9/sound/core/sound.c 

kernel-4.9/sound/core/control.c

---->snd_register_device_for_dev(int type, struct snd_card *card, int dev,struct file_operations *f_ops,void *private_data,char *name, struct device *device)---->preg->type = type;---->preg->card = card ? card->number : -1;---->preg->device = dev;---->preg->f_ops = f_ops;---->preg->private_data = private_data;---->snd_minors[minor] = preg;---->device_create(sound_class, device, MKDEV(major,minor),private_data, "%s", name);//dev节点         /dev/sound/controlC0

2.snd_ctl_create(struct snd_card *card)

---->static  struct snd_device_ops  ops = {.dev_free = snd_ctl_dev_free,.dev_register =snd_ctl_dev_register,.dev_disconnect = snd_ctl_dev_disconnect,};

创建snd_card的一个实例snd_card_new

kernel-4.9/sound/core/device.c

---->snd_device_new(card, SNDRV_DEV_CONTROL, card, &ops)----> list_add(&dev->list, &card->devices)

然后通过snd_card_register注册到内核中：kernel-4.9/sound/core/init.c

3.snd_card_register (struct snd_card *card)

----> device_create(sound_class, card->dev, MKDEV(0, 0), card, "card%i", card->number);
//dev节点         /dev/sound/card0
---->snd_device_register_all(card)---->list_for_each_entry(dev, &card->devices, list)----> dev->ops->dev_register(dev)
----> init_info_for_card(card);// 建立一些相应的proc和sysfs下的文件或属性节点

4.如何要完成一个声卡驱动

如果要完成一个完整的声卡驱动，其应该满足3步曲，那就是申请、初始化和注册才能成功。

（1）创建snd_card的一个实例snd_card_new

（2）初始化结构体

（3）通过snd_card_register注册到内核中