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libata-sff: avoid byte swapping in ata_sff_data_xfer()

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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>
This commit is contained in:
Sergei Shtylyov 2009-02-15 23:30:38 +04:00 committed by Jeff Garzik
parent 4da646b7b5
commit 2102d74973
1 changed files with 13 additions and 7 deletions
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20
drivers/ata/libata-sff.c
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@ -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++;
}