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

Takashi Iwai
2012-06-29T15:23:01Z

At Fri, 29 Jun 2012 20:34:24 +0530,
Laxman Dewangan wrote:
>
> Hi Takashi,
> Thanks for sample code. It helps lot.
>
> On Friday 29 June 2012 05:43 PM, Takashi Iwai wrote:
> > At Fri, 29 Jun 2012 15:53:15 +0530,
> > Laxman Dewangan wrote:
> >> Some of the ARM based soc allocate the writecombine dma buffer for
> >> pcm substreams. They have the same codes for managing this buffer.
> >> Moving this to the core/pcm files so that they can use that directly.
> >>
> >> Remove the code from Tegra PCM and use these new library function.
> >>
> >> This is enabled only for ARM specific and can be extended to other
> >> architecture if they support the writecombine dma buffer.
> >>
> >> This patch is based on detail discussion on patch:
> >> [PATCH] ASoC: snd_dmaengine: add common api for pcm_mmap
> >> And suggestion from Lars and Takashi.
> > Looking through your patch, I think an easier integration is just to
> > add writecombine option to memalloc.c which calls
> > dma_alloc_writecombine() instead of dma_alloc_coherent().
> >
> > The addition for mmap is still an open question. Again, an easier
> > option so far looks like just add the call of dma_alloc_writecombine()
> > in snd_pcm_lib_default_mmap(). Alternatively, we can create an
> > individual mmap pcm_ops as we discussed.
> >
> > Below is a totally untested patch, but you can imagine what I meant.
> >
> > After this change, replace with snd_pcm_lib_malloc_pages with
> > SNDRV_DMA_TYPE_DEV_WC, and that's all you need in the driver side.
>
> We can not use the snd_pcm_lib_malloc_pages() in the pcm_new callback
> because at this time the substream->runtime is not initialized and it
> leads to the kernel crash.
>
> I used the apis as
>
> int snd_soc_pcm_new_wc_dma_buffer(struct snd_soc_pcm_runtime *rtd,
> size_t max_bytes)
> {
> :::::::::::::
> substream = pcm->streams[SNDRV_PCM_STREAM_PLAYBACK].substream;
> if (substream) {
> substream->dma_buffer.dev.type = SNDRV_DMA_TYPE_DEV_WC;
> ret = snd_pcm_lib_malloc_pages(substream, max_bytes);
> if (ret)
> goto err;
> }
> ::::::::
> }
>
>
> int snd_pcm_lib_malloc_pages(struct snd_pcm_substream *substream, size_t
> size)
> {
> struct snd_pcm_runtime *runtime;
> struct snd_dma_buffer *dmab = NULL;
>
> if (PCM_RUNTIME_CHECK(substream))
> return -EINVAL;
>
> if (snd_BUG_ON(substream->dma_buffer.dev.type ==
> SNDRV_DMA_TYPE_UNKNOWN))
> return -EINVAL;
>
> runtime = substream->runtime;
>
> if (runtime->dma_buffer_p) {
> ---------------Kernel crash at this point ----------
>
> So I used the snd_dma_alloc_pages() from the driver to allocate WC memory.

snd_pcm_lib_malloc_pages() should be called only from hw_params.
Prior to that, you need to set up the dam_buffer type by calling
snd_pcm_lib_preallocate_pages() or
snd_pcm_lib_preallocate_pages_for_all() at the time to create a PCM
instance. The size can be 0 if not necessary to allocate there but
later on demand.

>
> > +/* 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)

Ah, OK.

thanks,

Takashi

> 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);
> }
>