USB: storage: set bounce limit for non-DMA-capable host controllers

This patch (as1175) makes usb-storage set a SCSI device's
request-queue bounce limit such that all buffers will be located in
addressable memory (i.e., not in high memory) if the host controller's
dma_mask is NULL.  This is necessary when the host controller doesn't
support DMA: If a buffer is in high memory then the both the virtual
and DMA addresses produced by the scatter-gather library will be NULL,
preventing the HCD from accessing the buffer's data.

In particular, the isp1760 driver needs this when used on a system
with more than 1 GB of memory.
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
CC: Matthew Dharm <mdharm-usb@one-eyed-alien.net>
Acked-by: Jens Axboe <jens.axboe@oracle.com>
Tested-by: Thomas Hommel <Thomas.Hommel@gefanuc.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/storage/scsiglue.c

@@ -129,6 +129,14 @@ static int slave_configure(struct scsi_device *sdev)
 					      max_sectors);
 	}
 
+	/* Some USB host controllers can't do DMA; they have to use PIO.
+	 * They indicate this by setting their dma_mask to NULL.  For
+	 * such controllers we need to make sure the block layer sets
+	 * up bounce buffers in addressable memory.
+	 */
+	if (!us->pusb_dev->bus->controller->dma_mask)
+		blk_queue_bounce_limit(sdev->request_queue, BLK_BOUNCE_HIGH);
+
 	/* We can't put these settings in slave_alloc() because that gets
 	 * called before the device type is known.  Consequently these
 	 * settings can't be overridden via the scsi devinfo mechanism. */