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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>
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commit
2102d74973
1 changed files with 13 additions and 7 deletions
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@ -727,17 +727,23 @@ unsigned int ata_sff_data_xfer(struct ata_device *dev, unsigned char *buf,
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else
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else
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iowrite16_rep(data_addr, buf, words);
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iowrite16_rep(data_addr, buf, words);
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/* Transfer trailing 1 byte, if any. */
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/* Transfer trailing byte, if any. */
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if (unlikely(buflen & 0x01)) {
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if (unlikely(buflen & 0x01)) {
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__le16 align_buf[1] = { 0 };
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unsigned char pad[2];
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unsigned char *trailing_buf = buf + buflen - 1;
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/* Point buf to the tail of buffer */
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buf += buflen - 1;
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/*
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* Use io*16_rep() accessors here as well to avoid pointlessly
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* swapping bytes to and fro on the big endian machines...
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*/
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if (rw == READ) {
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if (rw == READ) {
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align_buf[0] = cpu_to_le16(ioread16(data_addr));
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ioread16_rep(data_addr, pad, 1);
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memcpy(trailing_buf, align_buf, 1);
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*buf = pad[0];
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} else {
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} else {
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memcpy(align_buf, trailing_buf, 1);
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pad[0] = *buf;
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iowrite16(le16_to_cpu(align_buf[0]), data_addr);
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iowrite16_rep(data_addr, pad, 1);
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}
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}
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words++;
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words++;
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}
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}
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