Commit 37599f96 authored by Hans de Goede's avatar Hans de Goede Committed by Sarah Sharp
Browse files

uas: Make sure sg elements are properly aligned

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: default avatarHans de Goede <>
Signed-off-by: default avatarSarah Sharp <>
parent 8e453155
......@@ -925,6 +925,24 @@ 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));
return 0;
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