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Commit b475a3b8 authored by Tejun Heo's avatar Tejun Heo Committed by Jeff Garzik
Browse files

sata_via: explain the magic fix 



Add Joseph Chan's explanation of the problem and workaround to the
VT6421 magic fix.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Cc: Joseph Chan <JosephChan@via.com.tw>
Signed-off-by: default avatarJeff Garzik <jgarzik@redhat.com>
parent 386f40c8

drivers/ata/sata_via.c

+16 −2
Original line number Diff line number Diff line
@@ -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@via.com.tw>.

	 * Please add proper documentation if possible.

	 * is the fix from Joseph Chan <JosephChan@via.com.tw>.

	 *

	 * 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);