Re: [PATCH 0/3] ASoC: Move pcm writecombine dma buffer allocation to core

Laxman Dewangan
2012-06-29T15:07:24Z

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.

> +/* 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)

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);
}