ufs: adjust queue settings to PRDT limitations

The data byte count field of PRDT indicates the length of data block
which is a segment of data transfer for SCSI commands.  The value of
this field shall have Dword granularity and the the maximum of length
is 256KB.

This adjusts dma pad mask and max segment size to the above-mentioned
PRDT limitations.
Signed-off-by: Akinobu Mita <mita@fixstars.com>
Reviewed-by: Subhash Jadavani <subhashj@codeaurora.org>
Tested-by: Dolev Raviv <draviv@codeaurora.org>
Acked-by: Vinayak Holikatti <vinholikatti@gmail.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

drivers/scsi/ufs/ufshcd.c

@@ -2042,6 +2042,20 @@ int ufshcd_change_queue_depth(struct scsi_device *sdev, int depth, int reason)
 	return depth;
 }
 
+/**
+ * ufshcd_slave_configure - adjust SCSI device configurations
+ * @sdev: pointer to SCSI device
+ */
+static int ufshcd_slave_configure(struct scsi_device *sdev)
+{
+	struct request_queue *q = sdev->request_queue;
+
+	blk_queue_update_dma_pad(q, PRDT_DATA_BYTE_COUNT_PAD - 1);
+	blk_queue_max_segment_size(q, PRDT_DATA_BYTE_COUNT_MAX);
+
+	return 0;
+}
+
 /**
  * ufshcd_slave_destroy - remove SCSI device configurations
  * @sdev: pointer to SCSI device
@@ -3145,6 +3159,7 @@ static struct scsi_host_template ufshcd_driver_template = {
 	.proc_name		= UFSHCD,
 	.queuecommand		= ufshcd_queuecommand,
 	.slave_alloc		= ufshcd_slave_alloc,
+	.slave_configure	= ufshcd_slave_configure,
 	.slave_destroy		= ufshcd_slave_destroy,
 	.change_queue_depth	= ufshcd_change_queue_depth,
 	.eh_abort_handler	= ufshcd_abort,

drivers/scsi/ufs/ufshci.h

@@ -296,6 +296,11 @@ enum {
 	MASK_OCS			= 0x0F,
 };
 
+/* The maximum length of the data byte count field in the PRDT is 256KB */
+#define PRDT_DATA_BYTE_COUNT_MAX	(256 * 1024)
+/* The granularity of the data byte count field in the PRDT is 32-bit */
+#define PRDT_DATA_BYTE_COUNT_PAD	4
+
 /**
  * struct ufshcd_sg_entry - UFSHCI PRD Entry
  * @base_addr: Lower 32bit physical address DW-0