libata-sff: avoid byte swapping in ata_sff_data_xfer() (2102d749) · Commits · 戴 / test

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>

drivers/ata/libata-sff.c

+13 −7

Original line number	Diff line number	Diff line
		@@ -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++;
		}

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