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@xxxxxxxxxxxxx>
---
Oops, the subject got truncated -- resending...
The patch is against the recent Linus' tree but should apply to applicable
branch in the libata tree where it should probably wait for the next merge
window...
drivers/ata/libata-sff.c | 20 +++++++++++++-------
1 files changed, 13 insertions(+), 7 deletions(-)
Index: linux-2.6/drivers/ata/libata-sff.c
===================================================================
--- linux-2.6.orig/drivers/ata/libata-sff.c
+++ linux-2.6/drivers/ata/libata-sff.c
@@ -723,17 +723,23 @@ unsigned int ata_sff_data_xfer(struct at
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++;
}
--
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