USB: usb-storage: use adaptive DMA mask

This patch (as1060) makes usb-storage set the DMA alignment mask for
SCSI slaves to match the maxpacket size of the bulk-IN endpoint,
rather than always setting it to 511.  For full-speed devices that
mask is too restrictive, and wireless USB devices can have maxpacket
sizes larger than 512.
Signed-off-by: NAlan Stern <stern@rowland.harvard.edu>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

drivers/usb/storage/scsiglue.c

@@ -73,6 +73,7 @@ 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
@@ -84,12 +85,13 @@ static int slave_alloc (struct scsi_device *sdev)
 	/* 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.  Since high-speed bulk pipes have a maxpacket size
-	 * of 512, we'll use that as the scsi device queue's DMA alignment
-	 * mask.  Guaranteeing proper alignment of the first buffer will
-	 * have the desired effect because, except at the beginning and
-	 * the end, scatter-gather buffers follow page boundaries. */
-	blk_queue_update_dma_alignment(sdev->request_queue, (512 - 1));
+	 * transfer.  We'll use the maxpacket value of the bulk-IN pipe
+	 * to set the SCSI device queue's DMA alignment mask.
+	 */
+	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 */
 
 	/*
 	 * The UFI spec treates the Peripheral Qualifier bits in an