[PATCH v2 2/2] usb-storage: always set hw_max_sectors in slave_configure to avoid inappropriate clamping

[Tom Yan <tom.ty89@gmail.com>]

When the scsi request queue is initialized/allocated, the scsi driver clamps
hw_max_sectors against the dma max mapping size of sdev->host->dma_dev. The
device is currently inappriorate to use for USB drives.

Therefore, always (re)set hw_max_sectors in the usb drivers to invalidate the
clamping.

Signed-off-by: Tom Yan <tom.ty89@gmail.com>
---
 drivers/usb/storage/scsiglue.c | 37 ++++++++++++++++------------------
 drivers/usb/storage/uas.c      |  2 ++
 2 files changed, 19 insertions(+), 20 deletions(-)

diff --git a/drivers/usb/storage/scsiglue.c b/drivers/usb/storage/scsiglue.c
index e5a971b83e3f..1f60d777a7e8 100644
--- a/drivers/usb/storage/scsiglue.c
+++ b/drivers/usb/storage/scsiglue.c
@@ -120,6 +120,23 @@ static int slave_configure(struct scsi_device *sdev)
 		 * better throughput on most devices.
 		 */
 		blk_queue_max_hw_sectors(sdev->request_queue, 2048);
+	} else {
+		/*
+		 * Some devices are known to choke with anything larger. It seems like
+		 * the problem stems from the fact that original IDE controllers had
+		 * only an 8-bit register to hold the number of sectors in one transfer
+		 * and even those couldn't handle a full 256 sectors.
+		 *
+		 * Because we want to make sure we interoperate with as many devices as
+		 * possible, we will maintain a 240 sector transfer size limit for USB
+		 * Mass Storage devices.
+		 *
+		 * Tests show that other operating have similar limits with Microsoft
+		 * Windows 7 limiting transfers to 128 sectors for both USB2 and USB3
+		 * and Apple Mac OS X 10.11 limiting transfers to 256 sectors for USB2
+		 * and 2048 for USB3 devices.
+		 */
+		blk_queue_max_hw_sectors(sdev->request_queue, 240);
 	}
 
 	/*
@@ -626,26 +643,6 @@ static const struct scsi_host_template usb_stor_host_template = {
 	/* lots of sg segments can be handled */
 	.sg_tablesize =			SG_MAX_SEGMENTS,
 
-
-	/*
-	 * Limit the total size of a transfer to 120 KB.
-	 *
-	 * Some devices are known to choke with anything larger. It seems like
-	 * the problem stems from the fact that original IDE controllers had
-	 * only an 8-bit register to hold the number of sectors in one transfer
-	 * and even those couldn't handle a full 256 sectors.
-	 *
-	 * Because we want to make sure we interoperate with as many devices as
-	 * possible, we will maintain a 240 sector transfer size limit for USB
-	 * Mass Storage devices.
-	 *
-	 * Tests show that other operating have similar limits with Microsoft
-	 * Windows 7 limiting transfers to 128 sectors for both USB2 and USB3
-	 * and Apple Mac OS X 10.11 limiting transfers to 256 sectors for USB2
-	 * and 2048 for USB3 devices.
-	 */
-	.max_sectors =                  240,
-
 	/* emulated HBA */
 	.emulated =			1,
 
diff --git a/drivers/usb/storage/uas.c b/drivers/usb/storage/uas.c
index 813c49914b9a..592e1358822e 100644
--- a/drivers/usb/storage/uas.c
+++ b/drivers/usb/storage/uas.c
@@ -843,6 +843,8 @@ static int uas_slave_configure(struct scsi_device *sdev)
 		blk_queue_max_hw_sectors(sdev->request_queue, 240);
 	else if (us->pusb_dev->speed >= USB_SPEED_SUPER)
 		blk_queue_max_hw_sectors(sdev->request_queue, 2048);
+	else
+		blk_queue_max_hw_sectors(sdev->request_queue, SCSI_DEFAULT_MAX_SECTORS);
 
 	blk_queue_max_hw_sectors(sdev->request_queue,
 		min_t(size_t, queue_max_hw_sectors(sdev->request_queue),
-- 
2.28.0