[PATCH] usb: musb: host: Issue a memory barrier before staring the DMA

[Alan Stern]

On Thu, 5 Aug 2010, Santosh Shilimkar wrote:

> This patch fixes the issue which was observed while transfering
> a large file ( > 20MB) over USB (OMAP MUSB controller acts as USB host)
> to an attached USB thumb drive.
> 
> It was found that CDB field of CBW packet was set to 0x0. This was
> due to missing a barrier before DMA engine starts transfer.
> This  buffer is  allocated using dma_alloc_coherent which gives
> non-cacheble but bufferable memory and hence needed a write
> memory barrier to flush the write buffer.

If you see this problem when the controller uses DMA acting as a host,
does this mean the same problem might occur when it uses DMA acting as
a peripheral?

Alan Stern