Re: DMA API issues

[Takashi Iwai <tiwai@suse.de>]

At Wed, 23 Jun 2004 16:44:19 +0100,
Russell King wrote:
> 
> On Wed, Jun 23, 2004 at 05:36:57PM +0200, Takashi Iwai wrote:
> > > and a similar one for the ARM-specific "write combining" case (for
> > > framebuffers utilising the DMA API)?
> > 
> > pgprot_noncached() is used on many other architectures in fbmem.c
> > (well, not really, but the result is identical).
> > Should it be provided as another one, or is it used as default in
> > dma_mmap_coherent()?
> 
> The whole point is to kill the idea that drivers should have to know
> about page protection crap.  That should be wholely contained within
> the architecture implementation.

I agree.  My question is whether we need to handle different cases
with cached, non-cached and writecombine, according to the demand of
the driver.  In other words, do we always handle these mmap pages to
be non-cached (except for writecombine version)?


> > Also, it would be nice to have a version for sg-buffer, too.
> 
> Well, we don't have a sg-buffer version of dma_alloc_coherent(),
> so we don't have a sg-buffer version of dma_mmap_coherent().

That sound reasonable :)


Takashi