[alsa-devel] [PATCH 00/17] ASoC: Towards a generic dmaengine PCM driver

Mark Brown broonie at kernel.org
Tue Apr 16 17:33:36 CEST 2013

On Mon, Apr 15, 2013 at 07:19:47PM +0200, Lars-Peter Clausen wrote:

> This series adds a (almost) generic dmaengine PCM driver for ASoC. The tegra,
> spear, omap, imx, mxs, ep93xx and ux500 platforms are converted to use the
> generic driver instead of their own custom implementation. The driver builds on
> top of the dmaengine PCM library and adds the missing bits. The driver was

This all looks pretty good modulo testing and so on.

>  * The size of the pre-allocated audio buffer. All platforms seem use different
>    sizes and since some of them might be sensitive to changes to the buffer
>    size this series keeps the original size for now. But we should probably try
>    to decide on a sane default for this and maybe allow ASoC board drivers to
>    overwrite it somehow.

Or the platform for that matter of course.

> The driver uses snd_pcm_lib_preallocate_pages to preallocate the memory buffer.
> snd_pcm_lib_preallocate_pages internally uses dma_alloc_coherent, while most of
> the platforms converted in this series use dma_alloc_writecombine. Laxman
> Dewangan submitted a patch[1] a couple of months ago to add support for
> dma_alloc_writecombine to snd_pcm_lib_preallocate_pages, I always thought the
> patch had been merged, but it looks like I was mistaken. So if there are
> concerns about performance regression due to using coherent instead of
> writecombine mappings we'll have to postpone converting these platforms until
> Laxman's patch has been merged.

Can you resend that to Takashi, it sounds like if it's not been merged
it's probably due to it getting dropped rather than any great objection?
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