Messages in this thread Patch in this message | | | Subject | [PATCH] Call flush_dcache_page around PIO data transfers in libata-aff.c | From | Catalin Marinas <> | Date | Fri, 29 Jan 2010 16:10:26 +0000 |
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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).
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Jeff Garzik <jgarzik@pobox.com> ---
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.
Thanks.
drivers/ata/libata-sff.c | 6 ++++++ 1 files changed, 6 insertions(+), 0 deletions(-)
diff --git a/drivers/ata/libata-sff.c b/drivers/ata/libata-sff.c index 741065c..3d3c854 100644 --- a/drivers/ata/libata-sff.c +++ b/drivers/ata/libata-sff.c @@ -874,6 +874,9 @@ static void ata_pio_sector(struct ata_queued_cmd *qc) 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_queued_cmd *qc) do_write); } + if (!do_write) + flush_dcache_page(page); + qc->curbytes += qc->sect_size; qc->cursg_ofs += qc->sect_size;
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