On Wed, 10 Apr 2019, Bollinger, Seth wrote: > > On Apr 9, 2019, at 2:13 PM, Bollinger, Seth <Seth.Bollinger@xxxxxxxx<mailto:Seth.Bollinger@xxxxxxxx>> wrote: > > > > > Seth, you can try adding: > > > > > > blk_queue_virt_boundary(sdev->request_queue, 1024 - 1) > > > > > > in drivers/usb/storage/scsiglue.c:slave_alloc(), just after the call to > > > blk_queue_update_dma_alignment(). Perhaps that will help > > > > > > > I will do that as a test. However, I’m concerned that we’re solving only a specific case. Won’t it fail in a similar way if a different subsystem does the same thing (USB modem or > video drivers, etc.)? > > Just to follow up, this does seem to solve the specific problem. Great! Okay, here's an actual patch for you to try. I have removed the blk_queue_update_dma_alignment() call because it doesn't seem to be necessary. The starting location of each scatterlist element is unimportant; only the length matters. If this works, I will submit it as a bugfix for the kernel. Alan Stern drivers/usb/storage/scsiglue.c | 21 ++++++++------------- 1 file changed, 8 insertions(+), 13 deletions(-) Index: usb-4.x/drivers/usb/storage/scsiglue.c =================================================================== --- usb-4.x.orig/drivers/usb/storage/scsiglue.c +++ usb-4.x/drivers/usb/storage/scsiglue.c @@ -65,6 +65,7 @@ static const char* host_info(struct Scsi static int slave_alloc (struct scsi_device *sdev) { struct us_data *us = host_to_us(sdev->host); + int maxp; /* * Set the INQUIRY transfer length to 36. We don't use any of @@ -74,22 +75,16 @@ static int slave_alloc (struct scsi_devi sdev->inquiry_len = 36; /* - * USB has unusual DMA-alignment requirements: Although the - * starting address of each scatter-gather element doesn't matter, + * USB has unusual scatter-gather requirements: Although the + * starting address of each scatterlist 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. + * by the Bulk maxpacket value. Fortunately this value is always + * a power of 2. * - * 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. + * Inform the block layer about this requirement. */ - blk_queue_update_dma_alignment(sdev->request_queue, (512 - 1)); + maxp = usb_maxpacket(us->pusb_dev, us->recv_bulk_pipe, 0); + blk_queue_virt_boundary(sdev->request_queue, maxp - 1); /* Tell the SCSI layer if we know there is more than one LUN */ if (us->protocol == USB_PR_BULK && us->max_lun > 0)
