> -----Original Message----- > From: Mankad, Maulik Ojas > Sent: Tuesday, July 27, 2010 12:05 PM > To: linux-usb@xxxxxxxxxxxxxxx > Cc: Shilimkar, Santosh; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; linux- > omap@xxxxxxxxxxxxxxx > Subject: Issue with file transfers to a mass storage device on SMP system > > Hello, > > I am working on OMAP4 which has two ARM Cortex A9 microprocessors (SMP > system) with 2.6.35-rc5 kernel. > > I have an issue whereby transferring a large file (>20MB) over USB (OMAP > Mentor USB controller acts as USB host) to an attached USB thumb drive > fails. > > The USB analyzer trace shows that the 31 bytes CBW packet is corrupted and > device responds with a STALL when this issue occurs. > > Further it was found that the CBWCB field (the last 16 bytes which > contains > the command to be executed by the device) of the CBW packet was Zero in > the > failure case. Also the first 15 bytes of the CBW packet contained valid > data. > > The code snippet below from usb_stor_Bulk_transport () in > drivers/usb/storage/transport.c looks to be a problem area. > > /* copy the command payload */ > > memset(bcb->CDB, 0, sizeof(bcb->CDB)); > memcpy(bcb->CDB, srb->cmnd, bcb->Length); > > Looks like when the issue occurs the memory (bcb->CDB) is not yet updated > due to likely out of order execution due to SMP. > 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. In working scenario's, there might be a barrier in the path which is helping you. 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
