> From: Hans de Goede > > Copy the sg alignment trick from the usb-storage driver, without this I'm > seeing intermittent errors when using uas devices with an ehci controller. > > Signed-off-by: Hans de Goede <hdegoede@xxxxxxxxxx> > --- > drivers/usb/storage/uas.c | 18 ++++++++++++++++++ > 1 file changed, 18 insertions(+) > > diff --git a/drivers/usb/storage/uas.c b/drivers/usb/storage/uas.c > index 3c4cf1e..2b946dd 100644 > --- a/drivers/usb/storage/uas.c > +++ b/drivers/usb/storage/uas.c > @@ -928,6 +928,24 @@ static int uas_eh_bus_reset_handler(struct scsi_cmnd *cmnd) > static int uas_slave_alloc(struct scsi_device *sdev) > { > sdev->hostdata = (void *)sdev->host->hostdata; > + > + /* USB has unusual DMA-alignment requirements: Although the > + * starting address of each scatter-gather element doesn't matter, > + * the length of each element except the last must be divisible > + * by the Bulk maxpacket value. There's currently no way to > + * express this by block-layer constraints, so we'll cop out > + * and simply require addresses to be aligned at 512-byte > + * boundaries. This is okay since most block I/O involves > + * hardware sectors that are multiples of 512 bytes in length, > + * and since host controllers up through USB 2.0 have maxpacket > + * values no larger than 512. > + * > + * But it doesn't suffice for Wireless USB, where Bulk maxpacket > + * values can be as large as 2048. To make that work properly > + * will require changes to the block layer. > + */ > + blk_queue_update_dma_alignment(sdev->request_queue, (512 - 1)); The comment isn't true for anything connected to xhci. Pragmatically the solution might be reasonable though. (IIRC the usenet code knows whether it can do 'random' SG.) David -- 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