浅析ASoC-audio驱动oss框架下/dev/dsp与alsa框架下设备节点打开和创建简易流程
对于oss设备节点
1. soundcore_fops -- 提供主设备号为14的oss节点open("/dev/dsp")操作soundcore_open,最后将调用snd_pcm_oss_open
2. snd_pcm_oss_f_reg -- 提供最终的file->f_op应用程序调用方法集
对于alsa设备节点
1. snd_fops -- 提供主设备号为116的alsa节点open("/dev/pcmC0D1c")操作snd_open
2. snd_pcm_f_ops[2] -- 提供最终的file->f_op应用程序调用方法集snd_pcm_f_ops[0]用于放音,snd_pcm_f_ops[1]用于录音.
可能后面的流程都是混杂的,不能区分很清楚,所以先来看最直观的oss设备节点"/dev/dsp"打开流程[luther.gliethttp].
static const struct file_operations soundcore_fops=
{
/* We must have an owner or the module locking fails */
.owner = THIS_MODULE,
.open = soundcore_open, // 类似chrdev_open的实现,现在很多集中管理的驱动都这样
}; // 来界定设备[luther.gliethttp].
static const struct file_operations snd_pcm_oss_f_reg =
{
.owner = THIS_MODULE,
.read = snd_pcm_oss_read,
.write = snd_pcm_oss_write,
.open = snd_pcm_oss_open,
.release = snd_pcm_oss_release,
.poll = snd_pcm_oss_poll,
.unlocked_ioctl = snd_pcm_oss_ioctl,
.compat_ioctl = snd_pcm_oss_ioctl_compat,
.mmap = snd_pcm_oss_mmap,
};
我们先来看看打开/dev/dsp字符设备节点的流程[luther.gliethttp].
luther@gliethttp:~$ ll /dev/dsp
crw-rw----+ 1 root audio 14, 3 2009-08-15 14:59 /dev/dsp
module_init(init_soundcore); // 模块人口
static int __init init_soundcore(void)
{
// #define SOUND_MAJOR 14
if (register_chrdev(SOUND_MAJOR, "sound", &soundcore_fops)==-1) { // 主设备号为14的所有256个字符设备节点都将调用该方法集
printk(KERN_ERR "soundcore: sound device already in use.\n"); // 比如打开/dev/dsp设备,那么将首先执行这里的soundcore_open
return -EBUSY;
}
sound_class = class_create(THIS_MODULE, "sound"); // 创建/sys/class/sound类目录[luther.gliethttp]
if (IS_ERR(sound_class))
return PTR_ERR(sound_class);
return 0;
}
int soundcore_open(struct inode *inode, struct file *file)
{
int unit = iminor(inode); // 根据inode节点的minor次设备号锁定声卡设备,对于inode节点的自动创建在后面我们会慢慢谈到[luther.gliethttp].
struct sound_unit *s;
......
/*
* Allocations
*
* 0 *16 Mixers
* 1 *8 Sequencers
* 2 *16 Midi
* 3 *16 DSP
* 4 *16 SunDSP
* 5 *16 DSP16
* 6 -- sndstat (obsolete)
* 7 *16 unused
* 8 -- alternate sequencer (see above)
* 9 *16 raw synthesizer access
* 10 *16 unused
* 11 *16 unused
* 12 *16 unused
* 13 *16 unused
* 14 *16 unused
* 15 *16 unused
static struct sound_unit *chains[SOUND_STEP];
*/
chain=unit&0x0F; // 当前不超过16个SOUND_STEP
s = __look_for_unit(chain, unit); // 从chains[chain]全局链表上寻找索引号为unit的sound_unit.
if (s)
new_fops = fops_get(s->unit_fops); // 使用s->unit_fops=snd_pcm_oss_f_reg替换原有的soundcore_fops函数集
file->f_op = new_fops;
err = file->f_op->open(inode,file); // 使用snd_pcm_oss_open进一步打开
}
static struct sound_unit *__look_for_unit(int chain, int unit)
{
struct sound_unit *s;
s=chains[chain];
while(s && s->unit_minor <= unit)
{
if(s->unit_minor==unit)
return s; // ok,找到
s=s->next;
}
return NULL;
}
到目前为止我们粗略讨论了打开/dev/dsp设备节点的流程,下面我们继续看看创建/dev/dsp设备节点的流程是怎么样的[luther.gliethttp],
module_init(alsa_pcm_oss_init)还有一个module_init(alsa_mixer_oss_init)和alsa_pcm_oss_init过程差不多.
==>alsa_pcm_oss_init // 登记snd_pcm_oss_notify,同时为snd_pcm_devices链表上的的pcm设备执行snd_pcm_oss_register_minor函数
==*>snd_pcm_notify(&snd_pcm_oss_notify, 0) // 将snd_pcm_oss_notify追加到snd_pcm_notify_list通知链表
list_add_tail(¬ify->list, &snd_pcm_notify_list);
list_for_each_entry(pcm, &snd_pcm_devices, list) // 同时为snd_pcm_oss_notify遍历已经注册登记到snd_pcm_devices链表上的的pcm设备
notify->n_register(pcm); // 为他们分别执行snd_pcm_oss_notify的n_register方法[luther.gliehtttp]
static struct snd_pcm_notify snd_pcm_oss_notify =
{
.n_register = snd_pcm_oss_register_minor,
.n_disconnect = snd_pcm_oss_disconnect_minor,
.n_unregister = snd_pcm_oss_unregister_minor,
};
snd_pcm_oss_register_minor // 当检测到新的声卡设备时,就会调用该notifer函数,为其注册登记生成设备节点
==> register_oss_dsp(pcm, 0);和register_oss_dsp(pcm, 1); // index=0或者index=1,即第0个16组或者第1个16组
static void register_oss_dsp(struct snd_pcm *pcm, int index)
{
char name[128];
sprintf(name, "dsp%i%i", pcm->card->number, pcm->device);
if (snd_register_oss_device(SNDRV_OSS_DEVICE_TYPE_PCM,
pcm->card, index, &snd_pcm_oss_f_reg,// 实际完成控制设备的fops,即:snd_pcm_oss_f_reg
pcm, name) < 0) {
snd_printk(KERN_ERR "unable to register OSS PCM device %i:%i\n",
pcm->card->number, pcm->device);
}
}
snd_register_oss_device(int type, struct snd_card *card, int dev,
const struct file_operations *f_ops, void *private_data,
const char *name)
==> int minor = snd_oss_kernel_minor(type, card, dev); // minor = SNDRV_MINOR_OSS(card->number, (dev ? SNDRV_MINOR_OSS_PCM1 : SNDRV_MINOR_OSS_PCM));
==> preg->device = dev; // 我这里minor等于3
==> preg->f_ops = f_ops;
==> snd_oss_minors[minor] = preg; // 放到oss设备数组中,这样在snd_pcm_oss_open时可以打开
==> register_sound_special_device(f_ops, minor, carddev); // minor>=3
/**
* register_sound_special_device - register a special sound node
* @fops: File operations for the driver
* @unit: Unit number to allocate
* @dev: device pointer
*
* Allocate a special sound device by minor number from the sound
* subsystem. The allocated number is returned on succes. On failure
* a negative error code is returned.
*/
int register_sound_special_device(const struct file_operations *fops, int unit,
struct device *dev)
{
const int chain = unit % SOUND_STEP; // SOUND_STEP为16,分别代表主设备类型,每个主设备类型下可以追加n个同类型的音频设备.
int max_unit = 128 + chain;
const char *name;
char _name[16];
switch (chain) {
case 0:
name = "mixer";
break;
case 1:
name = "sequencer";
if (unit >= SOUND_STEP)
goto __unknown;
max_unit = unit + 1;
break;
case 2:
name = "midi";
break;
case 3:
name = "dsp";
break;
case 4:
name = "audio";
break;
case 8:
name = "sequencer2";
if (unit >= SOUND_STEP)
goto __unknown;
max_unit = unit + 1;
break;
case 9:
name = "dmmidi";
break;
case 10:
name = "dmfm";
break;
case 12:
name = "adsp";
break;
case 13:
name = "amidi";
break;
case 14:
name = "admmidi";
break;
default:
{
__unknown:
sprintf(_name, "unknown%d", chain);
if (unit >= SOUND_STEP)
strcat(_name, "-");
name = _name;
}
break;
}
return sound_insert_unit(&chains[chain], fops, -1, unit, max_unit,
name, S_IRUSR | S_IWUSR, dev); // 将方法集snd_pcm_oss_f_reg注册上去
}
static int sound_insert_unit(struct sound_unit **list, const struct file_operations *fops, int index, int low, int top, const char *name, umode_t mode, struct device *dev)
{
struct sound_unit *s = kmalloc(sizeof(*s), GFP_KERNEL);
int r;
if (!s)
return -ENOMEM; // index等于-1,表示动态获取一个可用的设备节点号.
spin_lock(&sound_loader_lock); // 每16个设备为一组,index表示第几组.
r = __sound_insert_unit(s, list, fops, index, low, top); // 插入到上面提到的chains[3]中,inode节点的minor设备号
spin_unlock(&sound_loader_lock); // 从最小值3开始按i*16方式递增,
// 即/dev/dsp的节点号为(14,3),
// /dev/dsp1的节点号为(14,19),
// /dev/dsp2的节点号为(14,35)依次类推[luther.gliethttp].
// 最后s->unit_minor=动态获取的一个空闲id
// s->unit_fops=snd_pcm_oss_f_reg
if (r < 0)
goto fail;
else if (r < SOUND_STEP)
sprintf(s->name, "sound/%s", name);
else
sprintf(s->name, "sound/%s%d", name, r / SOUND_STEP);
// 调用device_create广播设备信息到user space,udev创建
// 相应的字符设备节点/dev/dsp等[luther.gliethttp].
device_create(sound_class, dev, MKDEV(SOUND_MAJOR, s->unit_minor), // MKDEV(SOUND_MAJOR, s->unit_minor)为/dev/dsp设备的
NULL, s->name+6); // 节点号,主节点号SOUND_MAJOR等于14,子节点minor等于s->unit_minor
return r;
fail:
kfree(s);
return r;
}
上面snd_pcm_oss_notify中的n_register方法即:snd_pcm_oss_register_minor是在snd_pcm_oss_notify注册时主动执行的,
那在设备注册的时候又是怎么被动的引用n_register方法的呢?下面我们来看看,
先来看看设备注册,
/* audio subsystem */
static struct snd_soc_device TLG_snd_devdata = {
.machine = &snd_soc_machine_TLG,
.platform = &ep93xx_soc_platform,
.codec_dev = &soc_codec_dev_xxxxx,
};
static struct platform_device *TLG_snd_device;
module_init(TLG_init);
static int __init TLG_init(void) // 平台audio设备初始化入口
{
TLG_snd_device = platform_device_alloc("soc-audio", -1); // 他将被名为"soc-audio"的platform总线下的驱动程序驱动[luther.gliethttp]
platform_set_drvdata(TLG_snd_device, &TLG_snd_devdata);
TLG_snd_devdata.dev = &TLG_snd_device->dev;
ret = platform_device_add(TLG_snd_device);
}
static struct platform_driver soc_driver = {
.driver = {
.name = "soc-audio",
},
.probe = soc_probe,
.remove = soc_remove,
.suspend = soc_suspend,
.resume = soc_resume,
};
/* probes a new socdev */
static int soc_probe(struct platform_device *pdev)
{
// /* TLG audio machine driver */
// static struct snd_soc_machine snd_soc_machine_TLG = {
// .name = "TLG",
// .dai_link = TLG_dai, // /* CPU <--> Codec DAI links */核心在这里,Digital Audio Interface (DAI)
// .num_links = ARRAY_SIZE(TLG_dai),
// };
int ret = 0, i;
struct snd_soc_device *socdev = platform_get_drvdata(pdev);
struct snd_soc_machine *machine = socdev->machine;
struct snd_soc_platform *platform = socdev->platform;
struct snd_soc_codec_device *codec_dev = socdev->codec_dev;
if (machine->probe) { // snd_soc_machine_TLG
ret = machine->probe(pdev);
if(ret < 0)
return ret;
}
for (i = 0; i < machine->num_links; i++) {
// TLG_dai
struct snd_soc_cpu_dai *cpu_dai = machine->dai_link[i].cpu_dai;
if (cpu_dai->probe) {
ret = cpu_dai->probe(pdev);
if(ret < 0)
goto cpu_dai_err;
}
}
if (codec_dev->probe) { // soc_codec_dev_xxxxx
ret = codec_dev->probe(pdev); // xxxxx_soc_probe,完成节点创建工作
if(ret < 0)
goto cpu_dai_err;
}
// struct snd_pcm_ops ep93xx_pcm_ops = {
// .open = ep93xx_pcm_open,
// .close = ep93xx_pcm_close,
// .ioctl = snd_pcm_lib_ioctl,
// .hw_params = ep93xx_pcm_hw_params,
// .hw_free = ep93xx_pcm_hw_free,
// .prepare = ep93xx_pcm_prepare,
// .trigger = ep93xx_pcm_trigger,
// .pointer = ep93xx_pcm_pointer,
// .mmap = ep93xx_pcm_mmap,
// };
// struct snd_soc_platform ep93xx_soc_platform = {
// .name = "ep93xx-audio",
// .pcm_ops = &ep93xx_pcm_ops,
// .pcm_new = ep93xx_pcm_new,
// .pcm_free = ep93xx_pcm_free_dma_buffers,
// };
if (platform->probe) { // ep93xx_soc_platform
ret = platform->probe(pdev);
if(ret < 0)
goto platform_err;
}
......
}
struct snd_soc_codec_device soc_codec_dev_xxxxx中的xxxxx_soc_probe枚举函数
static int xxxxx_soc_probe(struct platform_device *pdev)
{
snd_soc_new_pcms(socdev, SNDRV_DEFAULT_IDX1, SNDRV_DEFAULT_STR1); // 创建alsa节点设备 -- major等于160的设备节点
ret = snd_soc_register_card(socdev); // 创建oss节点设备 -- major等于14的/dev/dsp等
}
xxxxx_soc_probe
==> snd_soc_new_pcms(socdev, SNDRV_DEFAULT_IDX1, SNDRV_DEFAULT_STR1);
==> soc_new_pcm(socdev, &card->dai_link[i], i); // 为每一个DAI数字音频接口流通道注册一个pcm.
/* create a new pcm */
static int soc_new_pcm(struct snd_soc_device *socdev,
struct snd_soc_dai_link *dai_link, int num)
{
struct snd_soc_codec *codec = socdev->codec;
struct snd_soc_codec_dai *codec_dai = dai_link->codec_dai;
struct snd_soc_cpu_dai *cpu_dai = dai_link->cpu_dai;
......
// 将ep9312开发板音频数据部分控制方法赋值给默认的soc_pcm_ops静态统一结构体[luther.gliethttp]
// socdev -- TLG_snd_devdata
// platform -- ep93xx_soc_platform
// pcm_ops -- ep93xx_pcm_ops
ret = snd_pcm_new(codec->card, new_name, codec->pcm_devs++, playback,
capture, &pcm);
......
// /* ASoC PCM operations */
// static struct snd_pcm_ops soc_pcm_ops = {
// .open = soc_pcm_open,
// .close = soc_codec_close,
// .hw_params = soc_pcm_hw_params,
// .hw_free = soc_pcm_hw_free,
// .prepare = soc_pcm_prepare,
// .trigger = soc_pcm_trigger,
// };
soc_pcm_ops.mmap = socdev->platform->pcm_ops->mmap; // 开发板自己的mmap方法
soc_pcm_ops.pointer = socdev->platform->pcm_ops->pointer;
soc_pcm_ops.ioctl = socdev->platform->pcm_ops->ioctl; // 开发板自己的ioctl方法
soc_pcm_ops.copy = socdev->platform->pcm_ops->copy;
soc_pcm_ops.silence = socdev->platform->pcm_ops->silence;
soc_pcm_ops.ack = socdev->platform->pcm_ops->ack;
soc_pcm_ops.page = socdev->platform->pcm_ops->page;
if (playback) // 放音通道,见下面[luther.gliethttp]
snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_PLAYBACK, &soc_pcm_ops); // 这样stream的ops就直接使用上了与platform平台相关的专有控制函数了.
if (capture) // 录音通道,见下面
snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_CAPTURE, &soc_pcm_ops);
ret = socdev->platform->pcm_new(codec->card, codec_dai, pcm);
if (ret < 0) {
printk(KERN_ERR "asoc: platform pcm constructor failed\n");
kfree(rtd);
return ret;
}
pcm->private_free = socdev->platform->pcm_free;
......
}
/**
* snd_pcm_set_ops - set the PCM operators
* @pcm: the pcm instance
* @direction: stream direction, SNDRV_PCM_STREAM_XXX
* @ops: the operator table
*
* Sets the given PCM operators to the pcm instance.
*/
void snd_pcm_set_ops(struct snd_pcm *pcm, int direction, struct snd_pcm_ops *ops)
{
struct snd_pcm_str *stream = &pcm->streams[direction]; // 有2种值:SNDRV_PCM_STREAM_PLAYBACK(放音)和SNDRV_PCM_STREAM_CAPTURE(录音)
struct snd_pcm_substream *substream; // pcm->streams[]在snd_pcm_new()中创建[luther.gliethttp].
for (substream = stream->substream; substream != NULL; substream = substream->next)
substream->ops = ops; // 遍历所有substream流通道,赋予其控制该stream流数据的该ops操作方法集soc_pcm_ops[luther.gliehttp]
}
==> snd_pcm_new(codec->card, new_name, codec->pcm_devs++, playback, capture, &pcm)
==> static struct snd_device_ops ops = {
.dev_free = snd_pcm_dev_free,
.dev_register = snd_pcm_dev_register,
.dev_disconnect = snd_pcm_dev_disconnect,
};
pcm->device = device;等于codec->pcm_devs++索引值
==> snd_device_new(card, SNDRV_DEV_PCM, pcm, &ops);
int snd_device_new(struct snd_card *card, snd_device_type_t type,
void *device_data, struct snd_device_ops *ops)
{
struct snd_device *dev;
......
dev = kzalloc(sizeof(*dev), GFP_KERNEL);
......
dev->ops = ops; // 上面snd_pcm_new()中static类型的ops方法集,
// 含有.dev_register = snd_pcm_dev_register
list_add(&dev->list, &card->devices); /* add to the head of list */
return 0;
}
下面是oss设备节点和alsa设备节点创建流程的核心部分[luther.gliethttp].
xxxxx_soc_probe
==> snd_soc_register_card(socdev)
==> snd_card_register(card)
==> snd_device_register_all(card)
/*
* register all the devices on the card.
* called from init.c
*/
int snd_device_register_all(struct snd_card *card)
{
struct snd_device *dev;
int err;
snd_assert(card != NULL, return -ENXIO);
list_for_each_entry(dev, &card->devices, list) { // 注册card设备链表上的所有DAI控制链路的stream流通道[luther.gliethttp].
if (dev->state == SNDRV_DEV_BUILD && dev->ops->dev_register) {
if ((err = dev->ops->dev_register(dev)) < 0) // 即:snd_pcm_dev_register
return err;
dev->state = SNDRV_DEV_REGISTERED;
}
}
return 0;
}
==> dev->ops->dev_register(dev) 即:snd_pcm_dev_register
/*
* snd_pcm_new
* static struct snd_device_ops ops = {
* .dev_free = snd_pcm_dev_free,
* .dev_register = snd_pcm_dev_register,
* .dev_disconnect = snd_pcm_dev_disconnect,
* };
* ==> snd_device_new(card, SNDRV_DEV_PCM, pcm, &ops)
*/
static int snd_pcm_dev_register(struct snd_device *device)
{
char str[16];
......
sprintf(str, "pcmC%iD%ip", pcm->card->number, pcm->device);
或
sprintf(str, "pcmC%iD%ic", pcm->card->number, pcm->device);
err = snd_register_device_for_dev(devtype, pcm->card,
pcm->device, // 这里的pcm->device就是snd_pcm_new()函数中codec->pcm_devs++
&snd_pcm_f_ops[cidx], // alsa方法集,包含录音和放音[luther.gliethttp]
pcm, str, dev); // 注册alsa设备节点
......
list_for_each_entry(notify, &snd_pcm_notify_list, list)
notify->n_register(pcm); // 调用上面介绍的snd_pcm_oss_register_minor注册notifier注册OSS设备节点
......
}
int snd_register_device_for_dev(int type, struct snd_card *card, int dev,
const struct file_operations *f_ops,
void *private_data,
const char *name, struct device *device)
{
......
preg->device = dev;
preg->f_ops = f_ops; // 对应&snd_pcm_f_ops[cidx]这个alsa方法集,包含录音和放音
#ifdef CONFIG_SND_DYNAMIC_MINORS
minor = snd_find_free_minor();
#else
minor = snd_kernel_minor(type, card, dev); // 这里的dev就是snd_pcm_new()函数中codec->pcm_devs++
if (minor >= 0 && snd_minors[minor]) // 定义最多256个minor设备#define SNDRV_OS_MINORS 256
minor = -EBUSY;
#endif
snd_minors[minor] = preg; // 记录到alsa设备维护静态数组中,当open时会查找对应的preg.
preg->dev = device_create(sound_class, device, MKDEV(major, minor), // uevnt将创建MKDEV(major, minor)节点alsa设备节点
private_data, "%s", name); // 该major在alsa_sound_init中,默认为
// static int major = CONFIG_SND_MAJOR;
// #define CONFIG_SND_MAJOR 116 /* standard configuration */
......
}
#define CONFIG_SND_MAJOR 116 /* standard configuration */
static int major = CONFIG_SND_MAJOR;
module_init(alsa_sound_init)
alsa_sound_init
==> register_chrdev(major, "alsa", &snd_fops) // 主设备号为116的所有设备都为alsa设备,节点方法集为snd_fops
static const struct file_operations snd_fops = // alsa的设备名为pcmC0D1c或pcmC0D1p等[luther.gliethttp].
{
.owner = THIS_MODULE,
.open = snd_open
};
snd_open
==> __snd_open(inode, file);
==> __snd_open
unsigned int minor = iminor(inode);
mptr = snd_minors[minor];
file->f_op = fops_get(mptr->f_ops);
file->f_op->open(inode, file);
const struct file_operations snd_pcm_f_ops[2] = {
{ // alsa使用到的SNDRV_PCM_STREAM_PLAYBACK放音方法集[luther.gliethttp]
.owner = THIS_MODULE,
.write = snd_pcm_write,
.aio_write = snd_pcm_aio_write,
.open = snd_pcm_playback_open,
.release = snd_pcm_release,
.poll = snd_pcm_playback_poll,
.unlocked_ioctl = snd_pcm_playback_ioctl,
.compat_ioctl = snd_pcm_ioctl_compat,
.mmap = snd_pcm_mmap,
.fasync = snd_pcm_fasync,
.get_unmapped_area = dummy_get_unmapped_area,
},
{ // alsa使用到的SNDRV_PCM_STREAM_CAPTURE录音方法集[luther.gliethttp]
.owner = THIS_MODULE,
.read = snd_pcm_read,
.aio_read = snd_pcm_aio_read,
.open = snd_pcm_capture_open,
.release = snd_pcm_release,
.poll = snd_pcm_capture_poll,
.unlocked_ioctl = snd_pcm_capture_ioctl,
.compat_ioctl = snd_pcm_ioctl_compat,
.mmap = snd_pcm_mmap,
.fasync = snd_pcm_fasync,
.get_unmapped_area = dummy_get_unmapped_area,
}
};
至此,/dev/dsp设备节点和alsa设备节点在udev的配合下就按上面简单叙述的流程创建完成了[luther.gliethttp].
