sata_via: magic vt6421 fix for transmission problems w/ WD drives

vt6421 has problems talking to recent WD drives.  It causes a lot of
transmission errors while high bandwidth transfer as reported in the
following bugzilla entry.

  https://bugzilla.kernel.org/show_bug.cgi?id=15173

Joseph Chan provided the following fix.  I don't have any idea what it
does but I can verify the issue is gone with the patch applied.

Signed-off-by: Tejun Heo <tj@kernel.org>
Originally-from: Joseph Chan <JosephChan@via.com.tw>
Reported-by: Jorrit Tijben <sjorrit@gmail.com>
Cc: stable@kernel.org
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>

1 files changed, 13 insertions, 0 deletions

diff --git a/drivers/ata/sata_via.c b/drivers/ata/sata_via.c
index 101d8c219caf..0ecd0f6aa2c0 100644
--- a/drivers/ata/sata_via.c
+++ b/drivers/ata/sata_via.c
@@ -575,6 +575,19 @@ static void svia_configure(struct pci_dev *pdev)
                 tmp8 |= NATIVE_MODE_ALL;
                 pci_write_config_byte(pdev, SATA_NATIVE_MODE, tmp8);
         }
+
+        /*
+         * vt6421 has problems talking to some drives.  The following
+         * is the magic fix from Joseph Chan <JosephChan@via.com.tw>.
+         * Please add proper documentation if possible.
+         *
+         * https://bugzilla.kernel.org/show_bug.cgi?id=15173
+         */
+        if (pdev->device == 0x3249) {
+                pci_read_config_byte(pdev, 0x52, &tmp8);
+                tmp8 |= 1 << 2;
+                pci_write_config_byte(pdev, 0x52, tmp8);
+        }
 }
 
 static int svia_init_one(struct pci_dev *pdev, const struct pci_device_id *ent)