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

[Laxman Dewangan <ldewangan@nvidia.com>]

On Friday 29 June 2012 08:52 PM, Takashi Iwai wrote:
> At Fri, 29 Jun 2012 20:34:24 +0530,
> Laxman Dewangan wrote:
>> Hi Takashi,
>> Thanks for sample code. It helps lot.
>>
>> 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.

It worked well. Cool implementation.

I will send the patch of memalloc and for Tegra actually using this feature.

Thanks for suggestion and help.


Laxman