[PATCH] Fix pio/mwdma programming on ata_piix.c

["Art Haas" <ahaas@airmail.net>]

Hi.

Back in the beginning of February I was sent a patch to test during the
time the CD-ROM identification bug was affecting my computer. The
first posting of the patch appeared on Feb. 3 with Tejun Heo writing:

> Hello, Art Haas, Alan.
> 
> Okay, here's another try at fixing the detection bug.  I went through
> intel ich docs and compared with the ide piix driver.  This patch
> fixes the following problems.
> 
> * Control bits in the timing register wasn't cleared properly while
>   programming PIO mode.
> 
> * MWDMA mode programming cleared the wrong part of control bits.  I
>   think this can fix your problem.
> 
> * MWDMA mode programming cleared udma_mask even when the controller
>   doesn't support UDMA.  This doesn't matter for your case.
> 
> Please test and report the result.  Thanks.

The patch and complete thread can be reviewed here:

http://marc.info/?l=linux-ide&m=117042956705812&w=2

Now that 2.6.22 is open for big modifications, and the queued libata
changes have been pulled by Linus, I'm wondering if the ata_piix.c patch
posted above should be sent. I've built all my kernels since the posting
with the patch and had no problems. As you write above, the patch does
fix some bugs, and as the thread progressed a cleanup or two in the code
was explained as a bug fix - the setting of the 'slave_data' variable
between lines 826 and 834 in particular.

Here's the patch against today's Linus tree if you feel it should make
it into 2.6.22.

Art Haas

diff --git a/drivers/ata/ata_piix.c b/drivers/ata/ata_piix.c
index 55d306a..26c8b5f 100644
--- a/drivers/ata/ata_piix.c
+++ b/drivers/ata/ata_piix.c
@@ -695,8 +695,14 @@ static void piix_set_piomode (struct ata_port *ap, struct ata_device *adev)
 	if (adev->class == ATA_DEV_ATA)
 		control |= 4;	/* PPE enable */
 
+	/* PIO configuration clears DTE unconditionally.  It will be
+	 * programmed in set_dmamode which is guaranteed to be called
+	 * after set_piomode if any DMA mode is available.
+	 */
 	pci_read_config_word(dev, master_port, &master_data);
 	if (is_slave) {
+		/* clear TIME1|IE1|PPE1|DTE1 */
+		master_data &= 0xff0f;
 		/* Enable SITRE (seperate slave timing register) */
 		master_data |= 0x4000;
 		/* enable PPE1, IE1 and TIME1 as needed */
@@ -704,12 +710,14 @@ static void piix_set_piomode (struct ata_port *ap, struct ata_device *adev)
 		pci_read_config_byte(dev, slave_port, &slave_data);
 		slave_data &= (ap->port_no ? 0x0f : 0xf0);
 		/* Load the timing nibble for this slave */
-		slave_data |= ((timings[pio][0] << 2) | timings[pio][1]) << (ap->port_no ? 4 : 0);
+		slave_data |= ((timings[pio][0] << 2) | timings[pio][1])
+						<< (ap->port_no ? 4 : 0);
 	} else {
-		/* Master keeps the bits in a different format */
-		master_data &= 0xccf8;
+		/* clear ISP|RCT|TIME0|IE0|PPE0|DTE0 */
+		master_data &= 0xccf0;
 		/* Enable PPE, IE and TIME as appropriate */
 		master_data |= control;
+		/* load ISP and RCT */
 		master_data |=
 			(timings[pio][0] << 12) |
 			(timings[pio][1] << 8);
@@ -826,7 +834,7 @@ static void do_pata_set_dmamode (struct ata_port *ap, struct ata_device *adev, i
 			master_data &= 0xFF4F;  /* Mask out IORDY|TIME1|DMAONLY */
 			master_data |= control << 4;
 			pci_read_config_byte(dev, 0x44, &slave_data);
-			slave_data &= (0x0F + 0xE1 * ap->port_no);
+			slave_data &= (ap->port_no ? 0x0f : 0xf0);
 			/* Load the matching timing */
 			slave_data |= ((timings[pio][0] << 2) | timings[pio][1]) << (ap->port_no ? 4 : 0);
 			pci_write_config_byte(dev, 0x44, slave_data);
@@ -838,8 +846,11 @@ static void do_pata_set_dmamode (struct ata_port *ap, struct ata_device *adev, i
 				(timings[pio][0] << 12) |
 				(timings[pio][1] << 8);
 		}
-		udma_enable &= ~(1 << devid);
-		pci_write_config_word(dev, master_port, master_data);
+
+		if (ap->udma_mask) {
+			udma_enable &= ~(1 << devid);
+			pci_write_config_word(dev, master_port, master_data);
+		}
 	}
 	/* Don't scribble on 0x48 if the controller does not support UDMA */
 	if (ap->udma_mask)

-- 
Man once surrendering his reason, has no remaining guard against absurdities
the most monstrous, and like a ship without rudder, is the sport of every wind.

-Thomas Jefferson to James Smith, 1822