On Tue, Jun 14, 2011 at 12:30:44AM +0900, KyongHo Cho wrote:

On Tue, Jun 14, 2011 at 12:07 AM, Arnd Bergmann [off-list ref] wrote:

quoted

I'm sure that the graphics people will disagree with you on that.
Having the frame buffer mapped in write-combine mode is rather
important when you want to efficiently output videos from your
CPU.

I agree with you.
But I am discussing about dma_alloc_writecombine() in ARM.
You can see that only ARM and AVR32 implement it and there are few
drivers which use it.
No function in dma_map_ops corresponds to dma_alloc_writecombine().
That's why Marek tried to add 'alloc_writecombine' to dma_map_ops.

FWIW, on ARMv6 and later hardware, the dma_alloc_coherent() provides
writecombine memory (i.e. Normal Noncacheable), so no need for
dma_alloc_writecombine(). On earlier architectures it is creating
Strongly Ordered mappings (no writecombine).

-- 
Catalin