From mboxrd@z Thu Jan 1 00:00:00 1970 From: akpm@linux-foundation.org Subject: [patch for 2.6.33? 1/1] ata: call flush_dcache_page() around PIO data transfers in libata-aff.c Date: Tue, 02 Feb 2010 14:11:08 -0800 Message-ID: <201002022211.o12MB8cJ017441@imap1.linux-foundation.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ANSI_X3.4-1968 Content-Transfer-Encoding: 8bit Return-path: Received: from smtp1.linux-foundation.org ([140.211.169.13]:47479 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756995Ab0BBWNR (ORCPT ); Tue, 2 Feb 2010 17:13:17 -0500 Sender: linux-ide-owner@vger.kernel.org List-Id: linux-ide@vger.kernel.org To: jeff@garzik.org Cc: linux-ide@vger.kernel.org, akpm@linux-foundation.org, catalin.marinas@arm.com, jgarzik@pobox.com, stable@kernel.org, tj@kernel.org From: Catalin Marinas Depending on the direction of the transfer, flush_dcache_page() must be called either before (ATA_TFLAG_WRITE) or after (!ATA_TFLAG_WRITE) the data copying to avoid D-cache aliasing with user space or I-D cache coherency issues (when reading data from an ATA device using PIO, the kernel dirties the D-cache but there is no flush_dcache_page() required on Harvard architectures). This patch allows the ARM boards to use a rootfs on CompactFlash with the PATA platform driver. As Anfei Zhou mentioned in a recent patch ("flush dcache before writing into page to avoid alias"), on some architectures there may be a performance benefit in differentiating the flush_dcache_page() calls based on whether the kernel or the user page needs flushing. IMHO, we should differentiate based on the direction (kernel reading or writing from/to such page). In the ARM case with PIPT Harvard caches (newer processors), the kernel reading from a page that may be mapped in user space shouldn't need cache flushing. The kernel writing to such page would require D-cache flushing because of coherency with the I-cache. Currently on ARM, the latter happens in both cases. Signed-off-by: Catalin Marinas Cc: Jeff Garzik Cc: Tejun Heo Cc: Signed-off-by: Andrew Morton --- drivers/ata/libata-sff.c | 6 ++++++ 1 file changed, 6 insertions(+) diff -puN drivers/ata/libata-sff.c~ata-call-flush_dcache_page-around-pio-data-transfers-in-libata-affc drivers/ata/libata-sff.c --- a/drivers/ata/libata-sff.c~ata-call-flush_dcache_page-around-pio-data-transfers-in-libata-affc +++ a/drivers/ata/libata-sff.c @@ -874,6 +874,9 @@ static void ata_pio_sector(struct ata_qu DPRINTK("data %s\n", qc->tf.flags & ATA_TFLAG_WRITE ? "write" : "read"); + if (do_write) + flush_dcache_page(page); + if (PageHighMem(page)) { unsigned long flags; @@ -893,6 +896,9 @@ static void ata_pio_sector(struct ata_qu do_write); } + if (!do_write) + flush_dcache_page(page); + qc->curbytes += qc->sect_size; qc->cursg_ofs += qc->sect_size; _