Subject: Re: [bg-linux] [PATCH 5/7] [RFC] force 32-byte aligned kmallocs

From: Kazutomo Yoshii <[email-masked]>
Date: Thu, 19 May 2011 20:32:14 -0500

On 05/19/2011 07:36 PM, Benjamin Herrenschmidt wrote:
> On Wed, 2011-05-18 at 16:24 -0500, Eric Van Hensbergen wrote:
>    
>> For BGP, it is convenient for 'kmalloc' to come back with 32-byte
>> aligned units for torus DMA
>>
>> Signed-off-by: Eric Van Hensbergen<[email-masked]>
>> ---
>>   arch/powerpc/include/asm/page_32.h |    2 +-
>>   1 files changed, 1 insertions(+), 1 deletions(-)
>>
>> diff --git a/arch/powerpc/include/asm/page_32.h b/arch/powerpc/include/asm/page_32.h
>> index 68d73b2..fb0a7ae 100644
>> --- a/arch/powerpc/include/asm/page_32.h
>> +++ b/arch/powerpc/include/asm/page_32.h
>> @@ -9,7 +9,7 @@
>>
>>   #define VM_DATA_DEFAULT_FLAGS	VM_DATA_DEFAULT_FLAGS32
>>
>> -#ifdef CONFIG_NOT_COHERENT_CACHE
>> +#if defined(CONFIG_NOT_COHERENT_CACHE) || defined(CONFIG_BGP)
>>   #define ARCH_DMA_MINALIGN	L1_CACHE_BYTES
>>   #endif
>>      
> Is DMA cache coherent on BG/P ? That's odd for a 4xx base :-)
>    

Actually DMA sends invalidate requests to the snoop unit(L2 level).
BGP SoC is a bit different from other 4xx base.

Some details can be found in
www.scc.acad.bg/documentation/team.pdf

- kaz

> Cheers,
> Ben.
>
>
>
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