At Fri, 29 Jun 2012 20:34:24 +0530, Laxman Dewangan wrote:

Hi Takashi, Thanks for sample code. It helps lot.

On Friday 29 June 2012 05:43 PM, Takashi Iwai wrote:

...

At Fri, 29 Jun 2012 15:53:15 +0530, Laxman Dewangan wrote:

...

Some of the ARM based soc allocate the writecombine dma buffer for pcm substreams. They have the same codes for managing this buffer. Moving this to the core/pcm files so that they can use that directly.

Remove the code from Tegra PCM and use these new library function.

This is enabled only for ARM specific and can be extended to other architecture if they support the writecombine dma buffer.

This patch is based on detail discussion on patch: [PATCH] ASoC: snd_dmaengine: add common api for pcm_mmap And suggestion from Lars and Takashi.

Looking through your patch, I think an easier integration is just to add writecombine option to memalloc.c which calls dma_alloc_writecombine() instead of dma_alloc_coherent().

The addition for mmap is still an open question. Again, an easier option so far looks like just add the call of dma_alloc_writecombine() in snd_pcm_lib_default_mmap(). Alternatively, we can create an individual mmap pcm_ops as we discussed.

Below is a totally untested patch, but you can imagine what I meant.

After this change, replace with snd_pcm_lib_malloc_pages with SNDRV_DMA_TYPE_DEV_WC, and that's all you need in the driver side.

We can not use the snd_pcm_lib_malloc_pages() in the pcm_new callback because at this time the substream->runtime is not initialized and it leads to the kernel crash.

I used the apis as

int snd_soc_pcm_new_wc_dma_buffer(struct snd_soc_pcm_runtime *rtd, size_t max_bytes) { ::::::::::::: substream = pcm->streams[SNDRV_PCM_STREAM_PLAYBACK].substream; if (substream) { substream->dma_buffer.dev.type = SNDRV_DMA_TYPE_DEV_WC; ret = snd_pcm_lib_malloc_pages(substream, max_bytes); if (ret) goto err; } :::::::: }

int snd_pcm_lib_malloc_pages(struct snd_pcm_substream *substream, size_t size) { struct snd_pcm_runtime *runtime; struct snd_dma_buffer *dmab = NULL;

     if (PCM_RUNTIME_CHECK(substream))
             return -EINVAL;

     if (snd_BUG_ON(substream->dma_buffer.dev.type ==
                    SNDRV_DMA_TYPE_UNKNOWN))
             return -EINVAL;

     runtime = substream->runtime;

     if (runtime->dma_buffer_p) {

---------------Kernel crash at this point ----------

So I used the snd_dma_alloc_pages() from the driver to allocate WC memory.

snd_pcm_lib_malloc_pages() should be called only from hw_params. Prior to that, you need to set up the dam_buffer type by calling snd_pcm_lib_preallocate_pages() or snd_pcm_lib_preallocate_pages_for_all() at the time to create a PCM instance. The size can be 0 if not necessary to allocate there but later on demand.

...

+/* allocate the coherent DMA pages */ +static void *snd_malloc_dev_pages(struct device *dev, size_t size, dma_addr_t *dma) +{

• return __snd_malloc_dev_pages(dev, size, dma, dma_alloc_coherent);

This does not get compiled in ARM because dma_alloc_coherant is macro defined as

#define dma_alloc_coherent(d, s, h, f) dma_alloc_attrs(d, s, h, f, NULL)

Ah, OK.

thanks,

Takashi

static inline void *dma_alloc_attrs(struct device *dev, size_t size, dma_addr_t *dma_handle, gfp_t flag, struct dma_attrs *attrs)

I fixed this by static void *_dma_alloc_coherent(struct device *dev, size_t size, dma_addr_t *dma_handle, gfp_t flag) { return dma_alloc_coherent(dev, size, dma_handle, flag); }

/* allocate the coherent DMA pages */ static void *snd_malloc_dev_pages(struct device *dev, size_t size, dma_addr_t *dma) { return _snd_malloc_dev_pages(dev, size, dma, _dma_alloc_coherent); }