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

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Date:	Fri, 29 Jun 2012 18:18:56 +0200
From:	Takashi Iwai <tiwai@...e.de>
To:	Lars-Peter Clausen <lars@...afoo.de>
Cc:	Laxman Dewangan <ldewangan@...dia.com>, "lrg@...com" <lrg@...com>,
	"broonie@...nsource.wolfsonmicro.com" 
	<broonie@...nsource.wolfsonmicro.com>,
	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

At Fri, 29 Jun 2012 18:06:52 +0200,
Lars-Peter Clausen wrote:
> 
> On 06/29/2012 05:04 PM, Laxman Dewangan wrote:
> > [...]
> > 
> > 
> >> +/* allocate the coherent DMA pages */
> >> +static void *snd_malloc_dev_pages(struct device *dev, size_t size,
> >> dma_addr_t *dma)
> >> +{
> >> +    return __snd_malloc_dev_pages(dev, size, dma, dma_alloc_coherent);
> > 
> > This does not get compiled in ARM because dma_alloc_coherant is macro
> > defined as
> > 
> > #define dma_alloc_coherent(d, s, h, f) dma_alloc_attrs(d, s, h, f, NULL)
> > 
> > static inline void *dma_alloc_attrs(struct device *dev, size_t size,
> >                                        dma_addr_t *dma_handle, gfp_t flag,
> >                                        struct dma_attrs *attrs)
> > 
> > 
> > I fixed this by
> > static void *_dma_alloc_coherent(struct device *dev, size_t size,
> >                 dma_addr_t *dma_handle, gfp_t flag)
> > {
> >         return dma_alloc_coherent(dev, size, dma_handle, flag);
> > }
> > 
> > /* allocate the coherent DMA pages */
> > static void *snd_malloc_dev_pages(struct device *dev, size_t size,
> > dma_addr_t *dma)
> > {
> >         return _snd_malloc_dev_pages(dev, size, dma, _dma_alloc_coherent);
> > }
> 
> I think all dma_alloc_* functions use dma_alloc_attrs internally these days.
> I think it might be a better idea just to use dma_alloc_attrs in
> __snd_malloc_dev_pages and just pass a dma_attrs struct instead of a function.
> 
> Something like:
> 
> static void *__snd_malloc_dev_pages(struct device *dev, size_t size,
> 			    dma_addr_t *dma, struct dma_attrs *attrs)
> {
> ....
> 	res = dma_alloc_attrs(dev, PAGE_SIZE << pg, dma, gfp_flags, attrs);
> ....
> }
> 
> 
> static void *snd_malloc_dev_pages(struct device *dev, size_t size,
> 	dma_addr_t *dma)
> {
> 	return __snd_malloc_dev_pages(dev, size, dma, NULL);
> }
> 
> static void *snd_malloc_dev_wc_pages(struct device *dev, size_t size,
> 	dma_addr_t *dma)
> {
> 	DEFINE_DMA_ATTRS(attrs);
> 	dma_set_attr(DMA_ATTR_WRITE_COMBINE, &attrs);
> 
> 	return __snd_malloc_dev_pages(dev, size, dma, &attrs);
> }
> 
> Same applies for freeing the memory again.

Yes, that'd be cleaner.
But I prefer the code still workable on 3.5-base kernel, which makes
easier to test and merge for 3.6, at first. 

So, let's clean up these indirect calls once after all things are
settled down at 3.6-rc1.  It can be applied even before 3.6-rc2.


Takashi
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