On Tue, Jun 14, 2011 at 12:30:44AM +0900, KyongHo Cho wrote:
On Tue, Jun 14, 2011 at 12:07 AM, Arnd Bergmann arnd@arndb.de wrote:
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).