linux-kernel - Re: AW: PowerPC PCI DMA issues (prefetch/coherency?)

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Message-ID: <4A487720.5080500@oxtel.com>
Date:	Mon, 29 Jun 2009 09:11:12 +0100
From:	Chris Pringle <chris.pringle@...el.com>
To:	Sergej.Stepanov@....de
CC:	scottwood@...escale.com, linuxppc-dev@...ts.ozlabs.org,
	linux-kernel@...r.kernel.org
Subject: Re: AW: PowerPC PCI DMA issues (prefetch/coherency?)

Hi Sergej,

I've attached the patch used to fix this issue. Both the patch to 
pgtable32.h and head_32.S are required in order to make it work. The 
change to pgtable32.h ensures that all pages are marked cache coherent 
(results in setting the M bit). The change to head_32.S ensures that the 
M bit is not unconditionally masked out - it should only be masked out 
if CPU_FTR_NEED_COHERENT is not set.

Hope this helps.

Cheers,
Chris

Sergej.Stepanov@....de wrote:
>> The other part of the fix is in asm-powerpc/pgtable32.h. _PAGE_BASE
>> needs _PAGE_COHERENT in order to work correctly, and in fact there is
>> now a comment in there to that affect in 2.6.29. Backporting that change
>> has made it work on 2.6.26. Both this patch, and the fix to head_32.S
>> are needed for it to work correctly on older kernels.
>>
>> Chris
>>     
>
> Hello Chris,
>
> sorry for dummy, but if it possible, could you, please, send a corresponding summary patch of backporting you've done for older kernels?
> or just summary of that changes once again?
>
> Many thanks
>
> Sergej.


-- 

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Chris Pringle
Software Engineer

Miranda Technologies Ltd.
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Tel. +44 1491 820206
Fax. +44 1491 820001
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View attachment "dma-cache-coherency-fix.patch" of type "text/x-patch" (2591 bytes)