> -----Original Message----- > From: Russell King - ARM Linux [mailto:linux@xxxxxxxxxxxxxxxx] > Sent: Tuesday, July 27, 2010 4:12 PM > To: Shilimkar, Santosh > Cc: Mankad, Maulik Ojas; linux-usb@xxxxxxxxxxxxxxx; linux- > omap@xxxxxxxxxxxxxxx; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx > Subject: Re: Issue with file transfers to a mass storage device on SMP > system > > On Tue, Jul 27, 2010 at 03:49:29PM +0530, Shilimkar, Santosh wrote: > > > On Tue, Jul 27, 2010 at 03:08:54PM +0530, Shilimkar, Santosh wrote: > > > > As discussed, the main reason is the cache maintenance isn't done on > > > > "bcb->CDB" buffers and hence the data remains in CPU write buffer > > > > instead of the physical memory on which DMA operates. > > > > > > struct bulk_cb_wrap { > > > __le32 Signature; /* contains 'USBC' */ > > > __u32 Tag; /* unique per command id */ > > > __le32 DataTransferLength; /* size of data */ > > > __u8 Flags; /* direction in bit 0 */ > > > __u8 Lun; /* LUN normally 0 */ > > > __u8 Length; /* of of the CDB */ > > > __u8 CDB[16]; /* max command */ > > > }; > > > > > > So, CDB is contained within bcb...bcb+sizeof(*bcb). > > > > > > The bcb is passed to usb_stor_bulk_transfer_buf: > > > > > > result = usb_stor_bulk_transfer_buf(us, us->send_bulk_pipe, > > > bcb, cbwlen, NULL); > > > > > > which fills it into a URB: > > > > > > usb_fill_bulk_urb(us->current_urb, us->pusb_dev, pipe, buf, > > > length, > > > usb_stor_blocking_completion, NULL); > > > > > > This sets the URB buffer pointers: > > > > > > urb->transfer_buffer = transfer_buffer; > > > urb->transfer_buffer_length = buffer_length; > > > > > > And this buffer should be dma-mapped and dma-unmapped as appropriate. > > > > > > Wasn't there an issue with the DMA mapping being used with a PIO USB > > > host recently? Is that the problem here? > > That's correct. > > The last issue was otherway round where we were doing map/unmpap on PIO > buffer. > > That's exactly what I said. > > > This issue is because "CDB[16]", is not cleaned up before merging it > into CBW. > > The CDB array is part of the CBW (struct bulk_cb_wrap). When the > struct bulk_cb_wrap is mapped for DMA, the CDB will also be as it > is contained entirely within the CBW structure. > > As USB deals with the whole of the CBW as one block, it can't be that > half of it is being DMA-mapped and the other half isn't - something > else must be going on. If the CDB was a separate chunk of memory, I > could believe what you're suggesting. > > What we _do_ know is that 2.6.35-rc5 misses Catalin's barrier patches > for readl+writel, which means that there are ordering issues between > writing to memory and writing to devices. This is what is going on > here, and it is confirmed by this: > > | (3)Using wmb() (Write memory barrier) before starting DMA transfer in > MUSB > | driver fixes the issue. > > from Maulik. The fix is to have Catalin's ordered IO accessors which > add the wmb() internally to writel() to ensure that memory accesses > are visible. We have already those patches Russell and still see the issue. I think WMB is helping because data is just 16 bytes which can reside in WB. Had it been a bigger buffer this wouldn't have worked. Will get back to you with more data on this. -- 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
