基于uda34x的ALSA声卡驱动之s3c24xx-pcm.c

#include
#include
#include
#include
#include
#include

#include
#include
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#include
#include
#include
#include

#include "s3c24xx-pcm.h"

#define S3C24XX_PCM_DEBUG 0
#if S3C24XX_PCM_DEBUG
#define DBG(x...) printk(KERN_DEBUG "s3c24xx-pcm: " x)
#else
#define DBG(x...)
#endif
//定义了一些缓冲区信息，在函数s3c24xx_pcm_open中用于初始化结构体substream->runtime->hw
static const struct snd_pcm_hardware s3c24xx_pcm_hardware = {
.info= SNDRV_PCM_INFO_INTERLEAVED |
SNDRV_PCM_INFO_BLOCK_TRANSFER |
SNDRV_PCM_INFO_MMAP |
SNDRV_PCM_INFO_MMAP_VALID |
SNDRV_PCM_INFO_PAUSE |
SNDRV_PCM_INFO_RESUME,
.formats= SNDRV_PCM_FMTBIT_S16_LE |
SNDRV_PCM_FMTBIT_U16_LE |
SNDRV_PCM_FMTBIT_U8 |
SNDRV_PCM_FMTBIT_S8,
.channels_min= 2,
.channels_max= 2,
.buffer_bytes_max= 128*1024,
.period_bytes_min= PAGE_SIZE,
.period_bytes_max= PAGE_SIZE*2,
.periods_min= 2,
.periods_max= 128,
.fifo_size= 32,
};
//缓存管理结构体在函数s3c24xx_pcm_open中挂到runtime->private_data上
//该结构体在函数s3c24xx_pcm_hw_params中被初始化
//所管理的缓存区域的分配在函数s3c24xx_pcm_preallocate_dma_buffer中
struct s3c24xx_runtime_data {
spinlock_t lock;
int state;
unsigned int dma_loaded;//已插入DMA备用存储链的存储段数
unsigned int dma_limit;//缓存段的最大数字
unsigned int dma_period;//每段缓存的最大存储数据量
dma_addr_t dma_start;//缓存区的开始地址
dma_addr_t dma_pos;//第一个未被插入DMA备用缓存链的存储段地址
dma_addr_t dma_end;//缓存区的尾地址
//结构params在函数s3c24xx_pcm_hw_params中被初始化prtd->params = dma;
struct s3c24xx_pcm_dma_params *params;
};

/* s3c24xx_pcm_enqueue
*
* place a dma buffer onto the queue for the dma system
* to handle.
*/
static void s3c24xx_pcm_enqueue(struct snd_pcm_substream *substream)
{
struct s3c24xx_runtime_data *prtd = substream->runtime->private_data;
dma_addr_t pos = prtd->dma_pos;
int ret;

DBG("Entered %sn", __func__);

while (prtd->dma_loaded < prtd->dma_limit) {
unsigned long len = prtd->dma_period;

DBG("dma_loaded: %dn", prtd->dma_loaded);

if ((pos + len) > prtd->dma_end) {
len = prtd->dma_end - pos;
DBG(KERN_DEBUG "%s: corrected dma len %ldn",
__func__, len);
}
//将缓存插入DMA备用缓存链，pos必须是物理地址，它将被写入DMA的初始化目的或源寄存器
ret = s3c2410_dma_enqueue(prtd->params->channel,
substream, pos, len);

if (ret == 0) {
prtd->dma_loaded++;
pos += prtd->dma_period;
if (pos >= prtd->dma_end)
pos = prtd->dma_start;
} else
break;
}

prtd->dma_pos = pos;
}
//当一段缓存用完时该函数将在中断处理函数中被调用
static void s3c24xx_audio_buffdone(struct s3c2410_dma_chan *channel,
void *dev_id, int size,
enum s3c2410_dma_buffresult result)
{
struct snd_pcm_substream *substream = dev_id;
struct s3c24xx_runtime_data *prtd;

DBG("Entered %sn", __func__);

if (result == S3C2410_RES_ABORT || result == S3C2410_RES_ERR)
return;

prtd = substream->runtime->private_data;

if (substream)
snd_pcm_period_elapsed(substream);

spin_lock(&prtd->lock);
if (prtd->state & ST_RUNNING) {
prtd->dma_loaded--;//用完一段缓存，将该缓存插入DMA备用链表尾。整个缓存区为一环形缓存区
s3c24xx_pcm_enqueue(substream);
}

spin_unlock(&prtd->lock);
}

static int s3c24xx_pcm_hw_params(struct snd_pcm_substream *substream,
struct snd_pcm_hw_params *params)
{
struct snd_pcm_runtime *runtime = substream->runtime;
struct s3c24xx_runtime_data *prtd = runtime->private_data;
struct snd_soc_pcm_runtime *rtd = substream->private_data;
struct s3c24xx_pcm_dma_params *dma = rtd->dai->cpu_dai->dma_data;
//从结构体params->intervals中获取缓冲区大小
unsigned long totbytes = params_buffer_bytes(params);
int ret = 0;

DBG("Entered %sn", __func__);

/* return if this is a bufferless transfer e.g.
* codec <--> BT codec or GSM modem -- lg FIXME */
if (!dma)
return 0;

/* this may get called several times by oss emulation
* with different params -HW */
if (prtd->params == NULL) {
/* prepare DMA */
//结构体dma为s3c24xx_i2s_pcm_stereo_out或s3c24xx_i2s_pcm_stereo_in
//在文件s3c24xx-i2s.c中定义
//结构体params为s3c24xx_runtime_data
prtd->params = dma;

DBG("params %p, client %p, channel %dn", prtd->params,
prtd->params->client, prtd->params->channel);
//申请一DMA通道
ret = s3c2410_dma_request(prtd->params->channel,
prtd->params->client, NULL);

if (ret < 0) {
DBG(KERN_ERR "failed to get dma channeln");
return ret;
}
}
//该函数主要实现chan->callback_fn = rtn;即让chan->callback_fn指向函数s3c24xx_audio_buffdone
s3c2410_dma_set_buffdone_fn(prtd->params->channel,
s3c24xx_audio_buffdone);
//用已分配的缓存区substream->dma_buffer区初始化substream->runtime的一些变量
snd_pcm_set_runtime_buffer(substream, &substream->dma_buffer);

runtime->dma_bytes = totbytes;

spin_lock_irq(&prtd->lock);
prtd->dma_loaded = 0;
prtd->dma_limit = runtime->hw.periods_min;
prtd->dma_period = params_period_bytes(params);//获取一段缓存的大小
prtd->dma_start = runtime->dma_addr;
prtd->dma_pos = prtd->dma_start;
prtd->dma_end = prtd->dma_start + totbytes;
spin_unlock_irq(&prtd->lock);

return 0;
}

static int s3c24xx_pcm_hw_free(struct snd_pcm_substream *substream)
{
struct s3c24xx_runtime_data *prtd = substream->runtime->private_data;

DBG("Entered %sn", __func__);

/* TODO - do we need to ensure DMA flushed */
snd_pcm_set_runtime_buffer(substream, NULL);

if (prtd->params) {
s3c2410_dma_free(prtd->params->channel, prtd->params->client);
prtd->params = NULL;
}

return 0;
}

static int s3c24xx_pcm_prepare(struct snd_pcm_substream *substream)
{
struct s3c24xx_runtime_data *prtd = substream->runtime->private_data;
int ret = 0;

DBG("Entered %sn", __func__);

/* return if this is a bufferless transfer e.g.
* codec <--> BT codec or GSM modem -- lg FIXME */
if (!prtd->params)
return 0;

/* channel needs configuring for mem=>device, increment memory addr,
* sync to pclk, half-word transfers to the IIS-FIFO. */
if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK) {//如果为放音
s3c2410_dma_devconfig(prtd->params->channel,//配置初始化目的寄存器和相应控制寄存器
S3C2410_DMASRC_MEM, S3C2410_DISRCC_INC |
S3C2410_DISRCC_APB, prtd->params->dma_addr);

s3c2410_dma_config(prtd->params->channel,
prtd->params->dma_size,//配置DMA控制寄存器，将配置值存于chan->dcon = dcon;
S3C2410_DCON_SYNC_PCLK |
S3C2410_DCON_HANDSHAKE);
} else {//录音，
s3c2410_dma_config(prtd->params->channel,
prtd->params->dma_size,//配置初始化源寄存器和相应控制寄存器
S3C2410_DCON_HANDSHAKE |
S3C2410_DCON_SYNC_PCLK);

s3c2410_dma_devconfig(prtd->params->channel,
S3C2410_DMASRC_HW, 0x3,
prtd->params->dma_addr);
}

/* flush the DMA channel */
s3c2410_dma_ctrl(prtd->params->channel, S3C2410_DMAOP_FLUSH);
prtd->dma_loaded = 0;
prtd->dma_pos = prtd->dma_start;

/* enqueue dma buffers */
s3c24xx_pcm_enqueue(substream);//将缓存链插入DMA备用缓存链

return ret;
}

static int s3c24xx_pcm_trigger(struct snd_pcm_substream *substream, int cmd)
{
struct s3c24xx_runtime_data *prtd = substream->runtime->private_data;
int ret = 0;

DBG("Entered %sn", __func__);

spin_lock(&prtd->lock);

switch (cmd) {
case SNDRV_PCM_TRIGGER_START:
case SNDRV_PCM_TRIGGER_RESUME:
case SNDRV_PCM_TRIGGER_PAUSE_RELEASE:
prtd->state |= ST_RUNNING;//装载DMA缓存，开始DMA数据传输
s3c2410_dma_ctrl(prtd->params->channel, S3C2410_DMAOP_START);
s3c2410_dma_ctrl(prtd->params->channel, S3C2410_DMAOP_STARTED);
break;