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

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Date:	Fri, 29 Jun 2012 21:19:29 +0530
From:	Laxman Dewangan <ldewangan@...dia.com>
To:	Takashi Iwai <tiwai@...e.de>
CC:	"lrg@...com" <lrg@...com>,
	"broonie@...nsource.wolfsonmicro.com" 
	<broonie@...nsource.wolfsonmicro.com>,
	"lars@...afoo.de" <lars@...afoo.de>,
	Stephen Warren <swarren@...dia.com>,
	"perex@...ex.cz" <perex@...ex.cz>,
	"clemens@...isch.de" <clemens@...isch.de>,
	"alsa-devel@...a-project.org" <alsa-devel@...a-project.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/3] ASoC: Move pcm writecombine dma buffer allocation
 to core

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
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