[PATCH] 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 clamping is apparently inappriorate to USB drives.

Either way we are calling blk_queue_max_hw_sectors() in the usb drivers for some (but not all) cases, which causes the clamping to be overriden (inconsistently) anyway.

Therefore the usb driver should always set hw_max_sectors and do the clamping against the right device itself.

Signed-off-by: Tom Yan <tom.ty89@gmail.com>
---
 drivers/usb/storage/scsiglue.c | 37 ++++++++++++++++------------------
 drivers/usb/storage/uas.c      | 23 ++++++++++++++++-----
 2 files changed, 35 insertions(+), 25 deletions(-)

diff --git a/drivers/usb/storage/scsiglue.c b/drivers/usb/storage/scsiglue.c
index e5a971b83e3f..804cbc0ba4da 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 08f9296431e9..cffa435afd84 100644
--- a/drivers/usb/storage/uas.c
+++ b/drivers/usb/storage/uas.c
@@ -827,11 +827,6 @@ static int uas_slave_alloc(struct scsi_device *sdev)
 	 */
 	blk_queue_update_dma_alignment(sdev->request_queue, (512 - 1));
 
-	if (devinfo->flags & US_FL_MAX_SECTORS_64)
-		blk_queue_max_hw_sectors(sdev->request_queue, 64);
-	else if (devinfo->flags & US_FL_MAX_SECTORS_240)
-		blk_queue_max_hw_sectors(sdev->request_queue, 240);
-
 	return 0;
 }
 
@@ -839,6 +834,24 @@ static int uas_slave_configure(struct scsi_device *sdev)
 {
 	struct uas_dev_info *devinfo = sdev->hostdata;
 
+	struct us_data *us = host_to_us(sdev->host);
+	struct device *dev = us->pusb_dev->bus->sysdev;
+
+	if (devinfo->flags & US_FL_MAX_SECTORS_64)
+		blk_queue_max_hw_sectors(sdev->request_queue, 64);
+	else if (devinfo->flags & US_FL_MAX_SECTORS_240)
+		blk_queue_max_hw_sectors(sdev->request_queue, 240);
+	else
+		blk_queue_max_hw_sectors(sdev->request_queue, SCSI_DEFAULT_MAX_SECTORS);
+
+	/*
+	 * The max_hw_sectors should be up to maximum size of a mapping for
+	 * the device. Otherwise, a DMA API might fail on swiotlb environment.
+	 */
+	blk_queue_max_hw_sectors(sdev->request_queue,
+		min_t(size_t, queue_max_hw_sectors(sdev->request_queue),
+		      dma_max_mapping_size(dev) >> SECTOR_SHIFT));
+
 	if (devinfo->flags & US_FL_NO_REPORT_OPCODES)
 		sdev->no_report_opcodes = 1;
 
-- 
2.28.0