linux-kernel - Re: [alsa-devel] [PATCH] ASoC: snd_dmaengine: add common api for pcm

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Date:	Thu, 28 Jun 2012 16:03:25 +0200
From:	Takashi Iwai <tiwai@...e.de>
To:	Lars-Peter Clausen <lars@...afoo.de>
Cc:	Laxman Dewangan <ldewangan@...dia.com>,
	"alsa-devel@...a-project.org" <alsa-devel@...a-project.org>,
	Stephen Warren <swarren@...dia.com>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"lrg@...com" <lrg@...com>
Subject: Re: [alsa-devel] [PATCH] ASoC: snd_dmaengine: add common api for	pcm_mmap

At Thu, 28 Jun 2012 14:44:43 +0200,
Lars-Peter Clausen wrote:
> 
> On 06/28/2012 01:56 PM, Laxman Dewangan wrote:
> > On Thursday 28 June 2012 04:21 PM, Mark Brown wrote:
> >> * PGP Signed by an unknown key
> >>
> >> On Thu, Jun 28, 2012 at 12:31:26PM +0530, Laxman Dewangan wrote:
> >>> The pcm mmap for the substream dma buffer is done using the
> >>> dma_mmap_writecombine().
> >>> Some of the chip sound driver like Spear, Tegra, Davinci,
> >>> ep93xx,snd_imx, snd_mxs, NUC900, OMAP, Samsung are doing this
> >>> mapping locally.
> >>> Add api in the snd dmaengine driver so that different client of
> >>> snd dmaengine can use this rather than implementing locally.
> >> OK, but I'd expect this to come along with one or more patches
> >> converting at least some of the users to the new API...
> > 
> > This is effort towards moving the Tegra pcm driver for dmangine based dma
> > driver inplace of legacy dma driver for Tegra which have private API.
> > 
> > Currently, following 4 pcm driver can use this API directly keeping that
> > they already using the generic snd dmaengine pcm driver.
> > ep93xx,
> > spear,
> > fsl,
> > mxs.
> > And Tegra will be next.
> > 
> > Other driver which can use this API are davinci, OMAP, samsung but because
> > they are not using the snd_dmaengine_pcm driver's api as of now so not be
> > very much useful for them.
> 
> Btw. all these drivers basically use the same code for buffer preallocation.
> Since how the buffer is mmaped is related to how it is allocated it might be
> worth to factor this out at the same time as well.

Hrm.  Do you mean hacking more on sound/core/memalloc.c, or sanitize
all these stuff?  Adding dma_alloc_writecombine() variant is easy, but
at the same time, I also would like to rip off this ugly thing.


Takashi
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