Add Joseph Chan's explanation of the problem and workaround to the VT6421 magic fix. Signed-off-by: Tejun Heo <tj@xxxxxxxxxx> Cc: Joseph Chan <JosephChan@xxxxxxxxxx> --- drivers/ata/sata_via.c | 18 ++++++++++++++++-- 1 file changed, 16 insertions(+), 2 deletions(-) diff --git a/drivers/ata/sata_via.c b/drivers/ata/sata_via.c index 0ecd0f6..4730c42 100644 --- a/drivers/ata/sata_via.c +++ b/drivers/ata/sata_via.c @@ -578,10 +578,24 @@ static void svia_configure(struct pci_dev *pdev) /* * vt6421 has problems talking to some drives. The following - * is the magic fix from Joseph Chan <JosephChan@xxxxxxxxxx>. - * Please add proper documentation if possible. + * is the fix from Joseph Chan <JosephChan@xxxxxxxxxx>. + * + * When host issues HOLD, device may send up to 20DW of data + * before acknowledging it with HOLDA and the host should be + * able to buffer them in FIFO. Unfortunately, some WD drives + * send upto 40DW before acknowledging HOLD and, in the + * default configuration, this ends up overflowing vt6421's + * FIFO, making the controller abort the transaction with + * R_ERR. + * + * Rx52[2] is the internal 128DW FIFO Flow control watermark + * adjusting mechanism enable bit and the default value 0 + * means host will issue HOLD to device when the left FIFO + * size goes below 32DW. Setting it to 1 makes the watermark + * 64DW. * * https://bugzilla.kernel.org/show_bug.cgi?id=15173 + * http://article.gmane.org/gmane.linux.ide/46352 */ if (pdev->device == 0x3249) { pci_read_config_byte(pdev, 0x52, &tmp8); -- To unsubscribe from this list: send the line "unsubscribe linux-ide" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
