[alsa-devel] Can I mmap buffer allocated using SNDRV_DMA_TYPE_CONTINUOUS?

[Takashi Iwai]

At Thu, 12 Jul 2007 19:24:24 +0530,
Pharaoh . wrote:
> 
> okay, I am on ARM..so better I do not use preallocation scheme with
> CONTINUOUS flag in case I want to mmap my dma buffer. In fact, I tried
> mmaping it, but it didn't work as expected.

On ARM, the mmap support is a bit tricky, so far.
The preallocation itself should work with SNDRV_DMA_TYPE_TYPE_DEV.
But you'd need the mmap PCM ops to call dma_mmap_coherent() there
instead of the default ALSA mmap handler.


Takashi

> 
> On 7/12/07, Takashi Iwai <tiwai at suse.de> wrote:
> > At Wed, 11 Jul 2007 18:17:49 +0530,
> > Pharaoh . wrote:
> > >
> > > On 7/11/07, Pharaoh . <pharaoh137 at gmail.com> wrote:
> > > >
> > > > Hi,
> > > > I have allocated the DMA buffer using snd_pcm_lib_malloc_pages() and
> > > > it was preallocated as:
> > > >
> > > > snd_pcm_lib_preallocate_pages_for_all(pcm,
> > > >                                              SNDRV_DMA_TYPE_CONTINUOUS,
> > > >                                              snd_dma_continuous_data
> > > >                                              (GFP_KERNEL),
> > > >                                              128 * 1024, 128 * 1024);
> > > >
> > > > Can I mmap such a dma buffer? I think yes...
> > > >
> > > > -pharaoh.
> > > >
> > >
> > >
> > > I dont think it can be mmapped.
> >
> > It can be basically, but not on all architectures.
> > For example, ARM has a problem with coherency.
> >
> >
> > Takashi
> >
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