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Re: [PATCH] mips: Add dma_mmap_coherent()

To: Takashi Iwai <tiwai@suse.de>
Subject: Re: [PATCH] mips: Add dma_mmap_coherent()
From: tsbogend@alpha.franken.de (Thomas Bogendoerfer)
Date: Fri, 22 Aug 2008 16:36:22 +0200
Cc: ralf@linux-mips.org, James Bottomley <James.Bottomley@HansenPartnership.com>, linux-mips@linux-mips.org, Parisc List <linux-parisc@vger.kernel.org>
In-reply-to: <s5h7ia9nya3.wl%tiwai@suse.de>
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <s5hzln7vd9d.wl%tiwai@suse.de> <1219255088.3258.45.camel@localhost.localdomain> <s5hr68ivfer.wl%tiwai@suse.de> <1219326912.3265.2.camel@localhost.localdomain> <s5hhc9enyqa.wl%tiwai@suse.de> <s5hfxoynyn4.wl%tiwai@suse.de> <20080821214118.GA12516@alpha.franken.de> <s5hbpzl8tvz.wl%tiwai@suse.de> <20080822094131.GA6717@alpha.franken.de> <s5h7ia9nya3.wl%tiwai@suse.de>
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On Fri, Aug 22, 2008 at 12:23:48PM +0200, Takashi Iwai wrote:
>       unsigned long prot = pgprot_val(_prot) & ~_CACHE_MASK;
> #ifdef CONFIG_SGI_IP32
> #ifdef CONFIG_CPU_R10000
>       prot = prot | _CACHE_UNCACHED_ACCELERATED;
> #else
>       prot = prot | _CACHE_CACHABLE_NO_WA;
> #endif
> #else
>       prot = prot | _CACHE_UNCACHED;
> #endif
>       return __pgprot(prot);

this won't work for recording channels on IP32, because the write trough
mapping will hide updates done via DMA.

I'd start with just

prot |= _CACHE_UNCACHED

and if some MIPS system needs more specific treatment, we just add
that later.

Thomas.

-- 
Crap can work. Given enough thrust pigs will fly, but it's not necessary a
good idea.                                                [ RFC1925, 2.3 ]

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