---

yaml
---
r: 104631
b: refs/heads/master
c: f756cbd
h: refs/heads/master
i:
  104629: 930e6c7
  104627: a7611a9
  104623: 500a753
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 86c57edf60f5c98adb496880f56cd0e5a3423153
+refs/heads/master: f756cbd458ab71c996a069cb3928fb1e2d7cd9cc

trunk/drivers/usb/storage/scsiglue.c

@@ -71,7 +71,6 @@ static const char* host_info(struct Scsi_Host *host)
 static int slave_alloc (struct scsi_device *sdev)
 {
 	struct us_data *us = host_to_us(sdev->host);
-	struct usb_host_endpoint *bulk_in_ep;
 
 	/*
 	 * Set the INQUIRY transfer length to 36.  We don't use any of
@@ -80,16 +79,22 @@ static int slave_alloc (struct scsi_device *sdev)
 	 */
 	sdev->inquiry_len = 36;
 
-	/* Scatter-gather buffers (all but the last) must have a length
-	 * divisible by the bulk maxpacket size.  Otherwise a data packet
-	 * would end up being short, causing a premature end to the data
-	 * transfer.  We'll use the maxpacket value of the bulk-IN pipe
-	 * to set the SCSI device queue's DMA alignment mask.
+	/* 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.
 	 */
-	bulk_in_ep = us->pusb_dev->ep_in[usb_pipeendpoint(us->recv_bulk_pipe)];
-	blk_queue_update_dma_alignment(sdev->request_queue,
-			le16_to_cpu(bulk_in_ep->desc.wMaxPacketSize) - 1);
-			/* wMaxPacketSize must be a power of 2 */
+	blk_queue_update_dma_alignment(sdev->request_queue, (512 - 1));
 
 	/*
 	 * The UFI spec treates the Peripheral Qualifier bits in an