At Thu, 28 Jun 2012 18:34:02 +0530, Laxman Dewangan wrote:

On Thursday 28 June 2012 06:27 PM, Takashi Iwai wrote:

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At Thu, 28 Jun 2012 18:05:53 +0530, Laxman Dewangan wrote:

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On Thursday 28 June 2012 05:58 PM, Mark Brown wrote:

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On Thu, Jun 28, 2012 at 02:30:26PM +0200, Lars-Peter Clausen wrote:

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On 06/28/2012 02:18 PM, Mark Brown wrote:

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Oh, dear - this means we don't actually have a generic API at all. Is there any effort being made to make this generally available?

Yes there is, and in fact in next/master there is generic dma_mmap_writecombine. I'm not quite sure how it behaves on non ARM archs though. But in theory it should fallback to a normal coherent mapping. Marek did a lot of work on this, I've put him on Cc.

So can we put the function snd_pcm_lib_writecombine_mmap() in the pcm_native.c and only export this api for ARM i.e. under macro #ifdef CONFIG_ARM so that ARM based SOCs like Tegra/epa3xx/mxs/spear can directly use that one? Or, wait for this common API until all ARCH support it?

I think it's fine to put it first in ALSA side with some ifdef. A similar trick is already found for snd_pcm_lib_mmap_iomem. See include/sound/pcm.h.

But, actually it's a still question what if an architecture doesn't support the mmap of writecombine at all. The proposed patch doesn't allow you to know whether writecombine-mmap is possible or not on the running architecture until you really try to call it and fail. It's a missing piece, IMO.

Lars wanted to move the buffer allocation also to common place.

Which common place?

Then how about this? create new file and header for snd-pcm-writecombine-buffer.c/.h and put this in sound/core. Select this file compilation through config SND_PCM_WRITECOMBINE_BUFFER which will be select this config through sound/soc/xxx/Kconfig if they want to use. This will provide three apis: new, free and mmap.

Way too much hustles than necessary...

Takashi