Linux音频OSS的buffer分析

统一术语

1. JZ 君正4760b mips

2. Audio buff 就是整个list_head+ list_node *4 + 整个音频区

3. APP 应用程序

整体使用框图

Buff分配流程

首先在probe JZ mixer设备的时候进行初始化DMA及缓冲buff. 在函数init_jz_i2s中调用audio_init_endpoint进行实始化。

fragsize= JZCODEC_RW_BUFFER_SIZE * PAGE_SIZE;

fragstotal= JZCODEC_RW_BUFFER_TOTAL;

audio_init_endpoint(&out_endpoint,fragsize, fragstotal);

audio_init_endpoint(&in_endpoint,fragsize, fragstotal);

fragsize= JZCODEC_RW_BUFFER_SIZE * PAGE_SIZE;fragstotal= JZCODEC_RW_BUFFER_TOTAL;audio_init_endpoint(&out_endpoint,fragsize, fragstotal);audio_init_endpoint(&in_endpoint,fragsize, fragstotal);

进入audio_init_endpoint函数，在这里先表一下in_endpoint和out_ endpoint结构体，初始化为0.

static audio_pipe out_endpoint = {

.mem = 0,

.savenode = 0,

.fragsize = 0,

.fragstotal = 0,

.trans_state = 0,

};

static audio_pipe in_endpoint= {

.mem = 0,

.savenode = 0,

.fragsize = 0,

.fragstotal = 0,

.trans_state = 0,

};

static audio_pipe out_endpoint = {.mem = 0,.savenode = 0,.fragsize = 0,.fragstotal = 0,.trans_state = 0,};static audio_pipe in_endpoint= {.mem = 0,.savenode = 0,.fragsize = 0,.fragstotal = 0,.trans_state = 0,};

void audio_init_endpoint(audio_pipe*endpoint, unsigned int pagesize,

unsigned int count)

{

audio_resizemem_endpoint(endpoint,pagesize, count);

spin_lock_init(&endpoint->lock);

init_waitqueue_head(&endpoint->q_full);

endpoint->avialable_couter= 0;

endpoint->filter= NULL;

if(endpoint == &in_endpoint) {

init_audio_audiodma(endpoint,CODEC_RMODE);

//INIT_WORK(&endpoint->work, audio_in_endpoint_work);

endpoint->handle= handle_in_endpoint_work;

}

if(endpoint == &out_endpoint) {

init_audio_audiodma(endpoint,CODEC_WMODE);

//INIT_WORK(&endpoint->work, audio_out_endpoint_work);

endpoint->handle= handle_out_endpoint_work;

}

int audio_resizemem_endpoint(audio_pipe*endpoint, unsigned int pagesize,

unsigned int count)

{

intret = init_audio_node(&endpoint->mem, pagesize, count,(int*)&endpoint->

fragmem_start);

if(ret) {

endpoint->fragsize= pagesize;

endpoint->fragstotal= count;

endpoint->memsize= ret;

}

returnret;

}

void audio_init_endpoint(audio_pipe*endpoint, unsigned int pagesize,unsigned int count){audio_resizemem_endpoint(endpoint,pagesize, count);spin_lock_init(&endpoint->lock);init_waitqueue_head(&endpoint->q_full);endpoint->avialable_couter= 0;endpoint->filter= NULL;if(endpoint == &in_endpoint) {init_audio_audiodma(endpoint,CODEC_RMODE);//INIT_WORK(&endpoint->work, audio_in_endpoint_work);endpoint->handle= handle_in_endpoint_work;}if(endpoint == &out_endpoint) {init_audio_audiodma(endpoint,CODEC_WMODE);//INIT_WORK(&endpoint->work, audio_out_endpoint_work);endpoint->handle= handle_out_endpoint_work;}}int audio_resizemem_endpoint(audio_pipe*endpoint, unsigned int pagesize,unsigned int count){intret = init_audio_node(&endpoint->mem, pagesize, count,(int*)&endpoint->fragmem_start);if(ret) {endpoint->fragsize= pagesize;endpoint->fragstotal= count;endpoint->memsize= ret;}returnret;}

我们进入audio_resizemem_endpoint分析内存的分配, 其中调用init_audio_node进行实质的
分配，先介绍一下这里的变量意义,了解了这些意义，分析起来就得心应手了，迫不及待
了。

JZCODEC_RW_BUFFER_SIZE // 1 * 4096

JZCODEC_RW_BUFFER_TOTAL; // 4个buff

unsignedint fact; //分配物理页的order

audio_node *pbuff; //代表1个audio node

audio_head *phead; //代表整个audiobuff 链表

unsignedint *mem; //分配得到整个audiobuff的虚拟地址

structlist_head *audio_wfree; //freebuff 链表

structlist_head *audio_wuse; //usebuff 链表

int memsize; //链表头+节点+audiobuff占用总空间

int datasize; //audiobuff占用的总空间

int headlistsize; //链表头+4个节点占用总空间

JZCODEC_RW_BUFFER_SIZE // 1 * 4096JZCODEC_RW_BUFFER_TOTAL; // 4个buffunsignedint fact; //分配物理页的orderaudio_node *pbuff; //代表1个audio nodeaudio_head *phead; //代表整个audiobuff 链表unsignedint *mem; //分配得到整个audiobuff的虚拟地址structlist_head *audio_wfree; //freebuff 链表structlist_head *audio_wuse; //usebuff 链表int memsize; //链表头+节点+audiobuff占用总空间int datasize; //audiobuff占用的总空间int headlistsize; //链表头+4个节点占用总空间

//Alloc memory first, to avail fail

datasize = ALIGN_PAGE_SIZE(pagesize * count);

headlistsize = ALIGN_PAGE_SIZE(count *sizeof(audio_node) + sizeof(audio_head));

memsize = headlistsize + datasize;

fact = get_order(memsize);

mem= (unsigned int *)__get_free_pages(GFP_KERNEL | GFP_DMA, fact);

//Alloc memory first, to avail faildatasize = ALIGN_PAGE_SIZE(pagesize * count);headlistsize = ALIGN_PAGE_SIZE(count *sizeof(audio_node) + sizeof(audio_head));memsize = headlistsize + datasize;fact = get_order(memsize);mem= (unsigned int *)__get_free_pages(GFP_KERNEL | GFP_DMA, fact);

首先获得整个audiobuff的大小 datasize, 再获得list_head + list_node * 4的大小
headlistsize, 然后计算总大小memsize, 用__get_free_pages分配连续的物理地址空间，这里
注意一下，返回的是物理地址。

//Free old buffer

if(*memory) {

phead = (audio_head *)*memory;

fact = phead->fact;

free_pages((unsignedlong)*memory, fact);

*memory = NULL;

}

*memory= mem;

//Free old bufferif(*memory) {phead = (audio_head *)*memory;fact = phead->fact;free_pages((unsignedlong)*memory, fact);*memory = NULL;}*memory= mem;

这里检查一下是不是有分配audiobuff, 如果有就释放掉，再将新分配的地址赋值给memory.
在mixer的ioctl中SNDCTL_DSP_SETFRAGMENT也会重新分配大小的。

phead = (audio_head *)*memory;

phead->fact = fact;

phead->listsize = headlistsize;

phead->datasize = datasize;

audio_wuse = &(phead->use);

audio_wfree = &(phead->free);

INIT_LIST_HEAD(audio_wuse);

INIT_LIST_HEAD(audio_wfree);

phead = (audio_head *)*memory;phead->fact = fact;phead->listsize = headlistsize;phead->datasize = datasize;audio_wuse = &(phead->use);audio_wfree = &(phead->free);INIT_LIST_HEAD(audio_wuse);INIT_LIST_HEAD(audio_wfree);

接下来就是给listhead赋值，然后初始化audio_wuse和audio_wfree链表。

pbuff= (audio_node *)((unsigned int)*memory + sizeof(audio_head));

*fragmem_start= (int)((unsigned int)*memory + headlistsize);

for(i = 0; i < count; i++) {

pbuff->pBuf = (unsigned int)*memory + headlistsize +pagesize * i;

pbuff->phyaddr = (unsigned int)virt_to_phys((void*)pbuff->pBuf);

pbuff->start = 0;

pbuff->end = 0;

DEBUG

pbuff->pBufID = i;

DPRINT_Q("audio_notebuffer[%d] = %x\n", i, (unsigned int)pbuff->pBuf);

list_add(&pbuff->list,audio_wfree);

pbuff++;

}

pbuff= (audio_node *)((unsigned int)*memory + sizeof(audio_head));*fragmem_start= (int)((unsigned int)*memory + headlistsize);for(i = 0; i < count; i++) {pbuff->pBuf = (unsigned int)*memory + headlistsize +pagesize * i;pbuff->phyaddr = (unsigned int)virt_to_phys((void*)pbuff->pBuf);pbuff->start = 0;pbuff->end = 0;#ifdef Q_DEBUGpbuff->pBufID = i;#endifDPRINT_Q("audio_notebuffer[%d] = %x\n", i, (unsigned int)pbuff->pBuf);list_add(&pbuff->list,audio_wfree);pbuff++;}

在这里将audio_wfree 链表全部初始化，注意此时wfree链表中有4个结点，wuse中

没有结点。

if (ret) {

endpoint->fragsize =pagesize;

endpoint->fragstotal =count;

endpoint->memsize = ret;

}

if (ret) {endpoint->fragsize =pagesize;endpoint->fragstotal =count;endpoint->memsize = ret;}

接下来返回到audio_resizemem_endpoint，将endpoint结构赋值。

Audio buff分配好后，再返回到audio_init_endpoint对DMA进行初始化，这里根据传
入的是play或者record进行初始化，大致上是雷同的，这里只分析 replay的初始化

if ((ch =jz_request_aic_dma(DMA_ID_I2S_TX,"audio dac", jz_i2s_dma_irq,IRQF_DISABLED,

endpoint)) < 0) {

printk(KERN_ERR "%s:can't reqeust DMA DAC channel.\n", __FUNCTION__);

return -1;

}

chan->io = i;

chan->dev_id = dev_id;

chan->dev_str = dev_str;

chan->fifo_addr = CPHYSADDR(AIC_DR);

switch (dev_id) {

case DMA_ID_AIC_TX:

chan->mode = DMA_AIC_TX_CMD_UNPACK | DMA_MODE_WRITE;

chan->source = DMAC_DRSR_RS_AICOUT;

break;

case DMA_ID_AIC_RX:

chan->mode = DMA_32BIT_RX_CMD | DMA_MODE_READ;

chan->source = DMAC_DRSR_RS_AICIN;

break;

default:

printk("JZ AIC: %s:%d,need fix !!!\n", __FUNCTION__, __LINE__);

BUG_ON(1);

}

if ((ch =jz_request_aic_dma(DMA_ID_I2S_TX,"audio dac", jz_i2s_dma_irq,IRQF_DISABLED,endpoint)) < 0) {printk(KERN_ERR "%s:can't reqeust DMA DAC channel.\n", __FUNCTION__);return -1;}chan->io = i;chan->dev_id = dev_id;chan->dev_str = dev_str;chan->fifo_addr = CPHYSADDR(AIC_DR);switch (dev_id) {case DMA_ID_AIC_TX:chan->mode = DMA_AIC_TX_CMD_UNPACK | DMA_MODE_WRITE;chan->source = DMAC_DRSR_RS_AICOUT;break;case DMA_ID_AIC_RX:chan->mode = DMA_32BIT_RX_CMD | DMA_MODE_READ;chan->source = DMAC_DRSR_RS_AICIN;break;default:printk("JZ AIC: %s:%d,need fix !!!\n", __FUNCTION__, __LINE__);BUG_ON(1);}

调用jz_request_aic_dma函数注册DMA中断，填写chan的模式与地址填充，最后启动
AIC DMA的时钟，再返回到init_audio_replaydma中，初始化寄存器，DMA就初始化OK了。
至此整个AUDIO BUFF就初始化完成了。

播放流程分析

先上图来说话:

首先进入jz_audio_write函数，里边有两个分支，根据模式进行区分的，第1种是使用
mmap方式传输的，由于我们要分析audio buff, 就不关注mmap方式了，各位如有想了解
的话，可以发与我讨论, dyronchina@gmail.com, 下边就直接进入audiobuff 方式的
jz_audio_write_data函数分析。

while(count >= pout_endpoint->fragsize) {

bat_cnt= endpoint_put_userdata(pout_endpoint,

&(buffer[usecount]),

pout_endpoint->fragsize);

//Prepare data success.

if(bat_cnt > 0) {

usecount+= bat_cnt;

count-= bat_cnt;

DPRINT("bat_cnt= %d\n", bat_cnt);

}

//Perhaps non node is avialable.

elseif (bat_cnt == 0) {

DPRINT("bat_cnt== 0\n");

break;

}

//Error occured.

else{

//break and handle prepared data.

if(usecount > 0) {

DPRINT("bat_cnt< 0, usecount > 0\n");

break;

}

//Has not prepared any data and return error when prepared data.

else{

DPRINT("bat_cnt< 0, usecount == 0\n");

returnbat_cnt;

}

while(count >= pout_endpoint->fragsize) {bat_cnt= endpoint_put_userdata(pout_endpoint,&(buffer[usecount]),pout_endpoint->fragsize);//Prepare data success.if(bat_cnt > 0) {usecount+= bat_cnt;count-= bat_cnt;DPRINT("bat_cnt= %d\n", bat_cnt);}//Perhaps non node is avialable.elseif (bat_cnt == 0) {DPRINT("bat_cnt== 0\n");break;}//Error occured.else{//break and handle prepared data.if(usecount > 0) {DPRINT("bat_cnt< 0, usecount > 0\n");break;}//Has not prepared any data and return error when prepared data.else{DPRINT("bat_cnt< 0, usecount == 0\n");returnbat_cnt;}}}

首先检查传入音频块的大小，必须大于fragsize(4096)，先来整体分析这个函数，然后
再进入内部分析细节，bat_cnt 根据返回值进行处理，返回0表明没有wfree节点，就直接
跳出，进行播放录音了。

DPRINT("<<<);

node= endpoint_get_outnode(endpoint);

if(!node)

return0;

if(copy_from_user((void *)node->pBuf, buffer, count)) {

printk("JZI2S: copy_from_user failed !\n");

return-EFAULT;

}

LEAVE();

returnendpoint_post_outnode(endpoint,node,count);

DPRINT("<<