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Re: ALSA on MIPS platform

To: Ralf Baechle <ralf@linux-mips.org>
Subject: Re: ALSA on MIPS platform
From: "Maciej W. Rozycki" <macro@linux-mips.org>
Date: Wed, 8 Aug 2007 13:40:51 +0100 (BST)
Cc: Takashi Iwai <tiwai@suse.de>, Atsushi Nemoto <anemo@mba.ocn.ne.jp>, jiankemeng@gmail.com, tiansm@lemote.com, linux-mips@linux-mips.org, alsa-devel@alsa-project.org, greg@kroah.com
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On Wed, 8 Aug 2007, Ralf Baechle wrote:

> > Yep, but OTOH, the arch code doesn't provide a proper standard way to
> > mmap the pages allocated via dma_alloc_coherent().  That's the missing
> > piece, especially on mips and sparc.  ARM has already one.
> > 
> > My wish is implementing dma_mmap_coherent() on all architectures, so
> > that the driver can use it safely without messy ifdefs.
> 
> Adding dma_mmap_coherent has been proposed in 2004 but the discussion for
> some reason went nowhere because it apparently isn't implementable on
> PARISC due to cache synonyms - on MIPS we'd solve those issues where they
> exist by using uncached or writethrough mappings, as apropriate.

 Hmm, why should everybody suffer from some limitation of some peculiar 
architecture?  I would suggest to let them find an architecture-specific 
way of addressing the problem -- they surely have a good control over 
their own code and can implement a workaround that would not impede all 
the others.

 Ralf, do you have an idea about what their issue exactly is?

  Maciej

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