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author | Sergei Shtylyov <sshtylyov@ru.mvista.com> | 2009-02-15 23:30:38 +0400 |
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committer | Jeff Garzik <jgarzik@redhat.com> | 2009-06-10 07:50:16 -0400 |
commit | 2102d7497393e982bf38ffe8f5fd3d487104880d (patch) | |
tree | 9693052c22db544384d433e95052d50779377c4a /drivers/ata/libata-sff.c | |
parent | 4da646b7b52552f3b43eae27ffa5aa2c200f6db6 (diff) | |
download | linux-2102d7497393e982bf38ffe8f5fd3d487104880d.tar.gz linux-2102d7497393e982bf38ffe8f5fd3d487104880d.tar.bz2 linux-2102d7497393e982bf38ffe8f5fd3d487104880d.zip |
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>
Diffstat (limited to 'drivers/ata/libata-sff.c')
-rw-r--r-- | drivers/ata/libata-sff.c | 20 |
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++; } |