[libata] change master/slave IDENTIFY order

2.6.21-rc has horrible problems with libata and PATA cable types (and
thus speeds). This occurs because Tejun fixed a pile of other bugs and
we now do cable detect enforcement for drive side detection properly.

Unfortunately we don't do the process around cable detection right. Tejun
identified the problem and pointed to the right Annex in the spec, this patch
implements the needed changes.

The basic requirement is that we have to identify the slave before the
master.

The patch switches the identify order so that we can do the drive side
detection correctly.

[NOTE: patch and description extracted from a larger work written
and signed-off-by Alan Cox]

Signed-off-by: Jeff Garzik <[e-mail]>

drivers/ata/libata-core.c

···
 	for (i = 0; i < ATA_MAX_DEVICES; i++)
 		ap->device[i].pio_mode = XFER_PIO_0;
 
-	/* read IDENTIFY page and configure devices */
-	for (i = 0; i < ATA_MAX_DEVICES; i++) {
+	/* read IDENTIFY page and configure devices. We have to do the identify
+	   specific sequence bass-ackwards so that PDIAG- is released by
+	   the slave device */
+
+	for (i = ATA_MAX_DEVICES - 1; i >=  0; i--) {
 		dev = &ap->device[i];
 
 		if (tries[i])
···
 				     dev->id);
 		if (rc)
 			goto fail;
+	}
+
+	/* After the identify sequence we can now set up the devices. We do
+	   this in the normal order so that the user doesn't get confused */
+
+	for(i = 0; i < ATA_MAX_DEVICES; i++) {
+		dev = &ap->device[i];
+		if (!ata_dev_enabled(dev))
+			continue;
 
 		ap->eh_context.i.flags |= ATA_EHI_PRINTINFO;
 		rc = ata_dev_configure(dev);