ALSA 驱动中dma的配置

/*
 * prepare DMA for pcm
 */
int i2s_dma_prepare(struct snd_pcm_substream *substream)
{
	struct snd_pcm_runtime *runtime = substream->runtime;
	struct sep0611_runtime_data *prtd = runtime->private_data;
	struct dma_info *p_dma_info;
	unsigned long i2s_fifo_width = 1;	/* 16 bits in default */
	int ret;
	
	/* we need call the i2s_dma_prepare after set hw_params, such as in pcm_prepare */
	if(runtime->format == 0){
		printk("ERR:please ensure the hw_params has been set correctly\n");
		return -EINVAL;
	}
	
	p_dma_info = kmalloc(sizeof(struct dma_info), GFP_KERNEL);
	if(!p_dma_info){
		return -ENOMEM;
	}
	
	if(substream->stream == SNDRV_PCM_STREAM_PLAYBACK){
		p_dma_info->trans_type = MEM_TO_DEV;
   		p_dma_info->src_addr = prtd->dma_buffer;
   		p_dma_info->dst_addr = I2S_BASE + I2