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Commit 2102d749 authored by Sergei Shtylyov's avatar Sergei Shtylyov Committed by Jeff Garzik
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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: default avatarSergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: default avatarJeff Garzik <jgarzik@redhat.com>
parent 4da646b7

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++;

	}