[PATCH v2 10/10] scsi: ufs: Micro-optimize ufshcd_map_sg()

[Bart Van Assche <bvanassche@acm.org>]

Replace two cpu_to_le32() calls by a single cpu_to_le64() call.

Additionally, issue a warning if the length of an scatter gather list
element exceeds what is allowed by the UFSHCI specification.

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
 drivers/scsi/ufs/ufshcd.c | 19 +++++++++++++------
 drivers/scsi/ufs/ufshci.h |  6 ++----
 2 files changed, 15 insertions(+), 10 deletions(-)

diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
index dde4d3f607f2..04cb67995750 100644
--- a/drivers/scsi/ufs/ufshcd.c
+++ b/drivers/scsi/ufs/ufshcd.c
@@ -2379,12 +2379,19 @@ static int ufshcd_map_sg(struct ufs_hba *hba, struct ufshcd_lrb *lrbp)
 		prd_table = lrbp->ucd_prdt_ptr;
 
 		scsi_for_each_sg(cmd, sg, sg_segments, i) {
-			prd_table[i].size  =
-				cpu_to_le32(((u32) sg_dma_len(sg))-1);
-			prd_table[i].base_addr =
-				cpu_to_le32(lower_32_bits(sg->dma_address));
-			prd_table[i].upper_addr =
-				cpu_to_le32(upper_32_bits(sg->dma_address));
+			const unsigned int len = sg_dma_len(sg);
+
+			/*
+			 * From the UFSHCI spec: "Data Byte Count (DBC): A '0'
+			 * based value that indicates the length, in bytes, of
+			 * the data block. A maximum of length of 256KB may
+			 * exist for any entry. Bits 1:0 of this field shall be
+			 * 11b to indicate Dword granularity. A value of '3'
+			 * indicates 4 bytes, '7' indicates 8 bytes, etc."
+			 */
+			WARN_ONCE(len > 256 * 1024, "len = %#x\n", len);
+			prd_table[i].size = cpu_to_le32(len - 1);
+			prd_table[i].addr = cpu_to_le64(sg->dma_address);
 			prd_table[i].reserved = 0;
 		}
 	} else {
diff --git a/drivers/scsi/ufs/ufshci.h b/drivers/scsi/ufs/ufshci.h
index f66cf9e477cb..6a295c88d850 100644
--- a/drivers/scsi/ufs/ufshci.h
+++ b/drivers/scsi/ufs/ufshci.h
@@ -415,14 +415,12 @@ enum {
 
 /**
  * struct ufshcd_sg_entry - UFSHCI PRD Entry
- * @base_addr: Lower 32bit physical address DW-0
- * @upper_addr: Upper 32bit physical address DW-1
+ * @addr: Physical address; DW-0 and DW-1.
  * @reserved: Reserved for future use DW-2
  * @size: size of physical segment DW-3
  */
 struct ufshcd_sg_entry {
-	__le32    base_addr;
-	__le32    upper_addr;
+	__le64    addr;
 	__le32    reserved;
 	__le32    size;
 };