libata-sff: avoid byte swapping in ata_sff_data_xfer()

Handling of the trailing byte in ata_sff_data_xfer() is suboptimal bacause:

- it always initializes the padding buffer to 0 which is not really needed in
  both the read and write cases;

- it has to use memcpy() to transfer a single byte from/to the padding buffer;

- it uses io{read|write}16() accessors which swap bytes on the big endian CPUs
  and so have to additionally convert the data from/to the little endian format
  instead of using io{read|write}16_rep() accessors which are not supposed to
  change the byte ordering.

Signed-off-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>

1 files changed, 13 insertions, 7 deletions

diff --git a/drivers/ata/libata-sff.c b/drivers/ata/libata-sff.c
index bb18415d3d63..bbbb1fab1755 100644
--- a/drivers/ata/libata-sff.c
+++ b/drivers/ata/libata-sff.c
@@ -727,17 +727,23 @@ unsigned int ata_sff_data_xfer(struct ata_device *dev, unsigned char *buf,
         else
                 iowrite16_rep(data_addr, buf, words);
 
-        /* Transfer trailing 1 byte, if any. */
+        /* Transfer trailing byte, if any. */
         if (unlikely(buflen & 0x01)) {
-                __le16 align_buf[1] = { 0 };
-                unsigned char *trailing_buf = buf + buflen - 1;
+                unsigned char pad[2];
 
+                /* Point buf to the tail of buffer */
+                buf += buflen - 1;
+
+                /*
+                 * Use io*16_rep() accessors here as well to avoid pointlessly
+                 * swapping bytes to and fro on the big endian machines...
+                 */
                 if (rw == READ) {
-                        align_buf[0] = cpu_to_le16(ioread16(data_addr));
-                        memcpy(trailing_buf, align_buf, 1);
+                        ioread16_rep(data_addr, pad, 1);
+                        *buf = pad[0];
                 } else {
-                        memcpy(align_buf, trailing_buf, 1);
-                        iowrite16(le16_to_cpu(align_buf[0]), data_addr);
+                        pad[0] = *buf;
+                        iowrite16_rep(data_addr, pad, 1);
                 }
                 words++;
         }