Re: [PATCH 2/2] ath9k: fix dma sync in rx path

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

2010/5/14 Felix Fietkau <nbd@openwrt.org>:
> On 2010-05-14 3:16 PM, tom.leiming@gmail.com wrote:
>> From: Ming Lei <tom.leiming@gmail.com>
>>
>> If buffer is to be accessed by cpu after dma transfer is over, but
>> between dma mapping and dma unmapping, we should use
>> dma_sync_single_for_cpu to sync the buffer between cpu with
>> device. And dma_sync_single_for_device is used to let
>> device gain the buffer again.
> I think this patch is wrong. On most MIPS devices,
> dma_sync_single_for_cpu is a no-op. In fact, with this patch, the rx
> path fails very quickly.

Sorry for  my  bad email client.

On most MIPS devices,  dma_sync_single_for_cpu does same things
almost with dma_unmap_single(plat_unmap_dma_mem is no-op). If
dma_unmap_single is enough, dma_sync_single_for_cpu is certainly
enough,
isn't it?

For the usage of dma_sync_single_for_cpu or dma_sync_single_for_device,
Documentation/DMA-API*.txt give more details.

> I believe keeping the dma_sync_single_for_device variant is necessary
> for all syncs.

Thanks,

-- 
Lei Ming