[libata] Call flush_dcache_page after PIO data transfers in libata-sff.c

flush_dcache_page() must be called 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>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>

drivers/ata/libata-sff.c

@@ -893,6 +893,9 @@ 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;