[PATCH 2/2] arm64: Support DMA_ATTR_WRITE_COMBINE

[Laura Abbott]

On 3/13/2014 10:52 AM, Catalin Marinas wrote:
> On Thu, Mar 13, 2014 at 05:45:16PM +0000, Laura Abbott wrote:
>> DMA_ATTR_WRITE_COMBINE is currently ignored. Set the pgprot
>> appropriately for non coherent opperations.
>>
>> Signed-off-by: Laura Abbott <lauraa at codeaurora.org>
>> ---
>>   Potential addition on top of the coherent work as well. Writecombine
>>   and dmacoherent seem to be the same at the moment but it might be
>>   good practice to have the two be separate?
>>
>>   arch/arm64/mm/dma-mapping.c | 13 +++++++++++--
>>   1 file changed, 11 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/arm64/mm/dma-mapping.c b/arch/arm64/mm/dma-mapping.c
>> index 9a639bf..d2c0027 100644
>> --- a/arch/arm64/mm/dma-mapping.c
>> +++ b/arch/arm64/mm/dma-mapping.c
>> @@ -29,6 +29,15 @@
>>   struct dma_map_ops *dma_ops;
>>   EXPORT_SYMBOL(dma_ops);
>>
>> +
>> +static inline pgprot_t __get_dma_pgprot(struct dma_attrs *attrs, pgprot_t prot)
>> +{
>> +	prot = dma_get_attr(DMA_ATTR_WRITE_COMBINE, attrs) ?
>> +			    pgprot_writecombine(prot) :
>> +			    pgprot_dmacoherent(prot);
>> +	return prot;
>> +}
>
> pgprot_writecombine and pgprot_dmacoherent are the same on arm64 (and
> ARMv6/v7). So when the DMA is coherent on an SoC, we need to leave the
> prot unchanged if !DMA_ATTR_WRITE_COMBINE.
>

Ah yes I missed that. I'll fix it up.

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