From: Catalin Marinas <catalin.marinas@xxxxxxx>
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 <catalin.marinas@xxxxxxx>
Cc: Jeff Garzik <jgarzik@xxxxxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
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;
_
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