At Fri, 03 Aug 2007 21:50:36 +0800,
Songmao Tian wrote:
> Atsushi Nemoto wrote:
> > On Wed, 01 Aug 2007 15:56:48 +0800, Songmao Tian <firstname.lastname@example.org> wrote:
> >> The problem is clear:
> >> 1. dma_alloc_noncoherent() return a non-cached address, and
> >> virt_to_page() need a cached logical addr (Have I named it right?)
> >> 2. mmaped dam buffer should be non-cached.
> >> We have a ugly patch, but we want to solve the problem cleanly, so can
> >> anyone show me the way?
> > virt_to_page() is used in many place in mm so making it robust might
> > affect performance. IMHO virt_to_page() seems too low-level as DMA
> > API.
> > If something like dma_virt_to_page(dev, cpu_addr) which can take a cpu
> > address returned by dma_xxx APIs was defined, MIPS can implement it
> > appropriately.
> > And then pgprot_noncached issues still exist...
> > ---
> > Atsushi Nemoto
> I agree, and I am investigating to implement a dma_map_coherent, but It
> seems dma_map_coherent doesn't solve all the problem and will change a
> lot of code:(
It won't be that much. You'll need to change snd_pcm_default_mmap()
in sound/core/pcm_native.c to call dma_mmap_coherent() directly
instead of nopage ops. But, this won't work with SG-buffers, which
requires some more additional works.