[alsa-devel] [PATCH 0/3] ASoC: Move pcm writecombine dma buffer allocation to core

[Lars-Peter Clausen]

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.

- Lars