Re: [PATCH v2 1/5] x86: make dma_alloc_coherent() return zeroedmemory if CMA is enabled

From: Akinobu Mita
Date: Thu Jan 16 2014 - 18:34:47 EST

2014/1/16 Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>:
> On Tue, Jan 14, 2014 at 11:13:46PM +0900, Akinobu Mita wrote:
>> Calling dma_alloc_coherent() with __GFP_ZERO must return zeroed memory.
>> But when the contiguous memory allocator (CMA) is enabled on x86 and
>> the memory region is allocated by dma_alloc_from_contiguous(), it
>> doesn't return zeroed memory. Because dma_generic_alloc_coherent()
> So why not fix it there to return zeroed out memory?

I thought it looked nicer than this patch as we can remove memset
from all caller of dma_alloc_from_contiguous(). But if I look at
the caller on arm, we can't simply remove the memset because
__dma_clear_buffer() is used there for ensuring cache flushing and
it is used in many places.

Of course we can do redundant memset in dma_alloc_from_contiguous(),
but now I think this patch is less impact for fixing this problem.
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