> -----Original Message----- > From: Alan Stern [mailto:stern@xxxxxxxxxxxxxxxxxxx] > Sent: Thursday, August 05, 2010 8:34 PM > To: Shilimkar, Santosh > Cc: linux-usb@xxxxxxxxxxxxxxx; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; > Mankad, Maulik Ojas; Russell King; Felipe Balbi > Subject: Re: [PATCH] usb: musb: host: Issue a memory barrier before > staring the DMA > > 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? > The peripheral USB drivers seems to have using standard kernel dma-mapping framework which internally takes care of the ordering issues. This is one of the cases where buffer is allocated using "dma_alloc_coherent" for which except ordering issue , there is no maintainace is necessary. Regards, Santosh -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
