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Re: [PATCH 3/5] ALSA: pcm - fix page conversion on non-coherent MIPS arc

To: Ralf Baechle <ralf@linux-mips.org>
Subject: Re: [PATCH 3/5] ALSA: pcm - fix page conversion on non-coherent MIPS arch
From: Takashi Iwai <tiwai@suse.de>
Date: Fri, 27 Nov 2009 10:20:12 +0100
Cc: alsa-devel@alsa-project.org, Wu Zhangjin <wuzhangjin@gmail.com>, Thomas Bogendoerfer <tsbogend@alpha.franken.de>, linux-mips@linux-mips.org, Benjamin Herrenschmidt <benh@kernel.crashing.org>, Kumar Gala <galak@gate.crashing.org>, Becky Bruce <beckyb@kernel.crashing.org>
In-reply-to: <20091127084635.GA18741@linux-mips.org>
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At Fri, 27 Nov 2009 08:46:35 +0000,
Ralf Baechle wrote:
> 
> On Thu, Nov 26, 2009 at 04:13:06PM +0100, Takashi Iwai wrote:
> 
> > The non-coherent MIPS arch doesn't give the correct address by a simple
> > virt_to_page() for pages allocated via dma_alloc_coherent().
> > 
> > Original patch by Wu Zhangjin <wuzj@lemote.com>.  A proper check of the
> > buffer allocation type was added to avoid the wrong conversion.
> 
> The origins of this patch go back far further.  The oldest patch I could
> find which is a superset of this was written by Atsushi Nemoto and
> various incarnations of it have been sumitted to and reject by me
> a number of times through the years.
> 
> > Note that this doesn't fix perfectly: the pages should be marked with
> > proper pgprot value.  This will be done in a future implementation like
> > the conversion to dma_mmap_coherent().
> > 
> > Signed-off-by: Takashi Iwai <tiwai@suse.de>
> 
> So while this is ugly I don't think this patch will actually make the
> the situation worse for any MIPS platform.  So with both eyes closed:
> 
> Acked-by: Ralf Baechle <ralf@linux-mips.org>

I added your ack with the comment about the origins to the GIT
commit now.

Thanks for closing your eyes ;)  Hopefully this hack can be removed
again shortly...


Takashi

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