At Thu, 28 Jun 2012 18:05:53 +0530, Laxman Dewangan wrote:
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:
On 06/28/2012 02:18 PM, Mark Brown wrote:
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.
Takashi