Re: [PATCH][RFC] asm-generic:remove calling flush_write_buffers() in dma_sync_*_for_cpu

[Ming Lei <tom.leiming@gmail.com>]

2009/6/29 Joerg Roedel <joerg.roedel@amd.com>:
>>
>> IMHO, even we do not call flush_write_buffer(), CPU can read correct
>> data from the
>> dma buffer since write buffer can't affect cache, right?
>
> flush_write_buffer is not about cache flushing. It is about read/write
> reordering in the CPU. Think of it as a memory barrier. On most x86

You mean we may need a memory barrier between writing data from bouncing buffer
to dma buffer and reading data from dma buffer, do you?

> systems this function is therefore a nop. Cache flushing for
> architectures without cache-coherent DMA is typically handled in their
> low-level dma-api code (I have seen that at least in parisc32).



-- 
Lei Ming