From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754053AbZBOTa1 (ORCPT ); Sun, 15 Feb 2009 14:30:27 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751355AbZBOTaR (ORCPT ); Sun, 15 Feb 2009 14:30:17 -0500 Received: from rtsoft3.corbina.net ([85.21.88.6]:26210 "EHLO buildserver.ru.mvista.com" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1751095AbZBOTaQ (ORCPT ); Sun, 15 Feb 2009 14:30:16 -0500 From: Sergei Shtylyov Organization: MontaVista Software Inc. To: jgarzik@pobox.com Subject: [PATCH 2/2 resend] libata-sff: avoid byte swapping in ata_sff_data_xfer() Date: Sun, 15 Feb 2009 23:30:38 +0400 User-Agent: KMail/1.5 Cc: linux-ide@vger.kernel.org, linux-kernel@vger.kernel.org, alan@lxorguk.ukuu.org.uk MIME-Version: 1.0 Content-Disposition: inline Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Message-Id: <200902152230.38271.sshtylyov@ru.mvista.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 --- Oops, the subject got truncated -- resending... The patch is against the recent Linus' tree but should apply to applicable branch in the libata tree where it should probably wait for the next merge window... drivers/ata/libata-sff.c | 20 +++++++++++++------- 1 files changed, 13 insertions(+), 7 deletions(-) Index: linux-2.6/drivers/ata/libata-sff.c =================================================================== --- linux-2.6.orig/drivers/ata/libata-sff.c +++ linux-2.6/drivers/ata/libata-sff.c @@ -723,17 +723,23 @@ unsigned int ata_sff_data_xfer(struct at 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++; }