[PATCH v2] libata-sff: Don't scan disabled ports when checking for legacy mode.

[Darren Stevens <darren@stevens-zone.net>]

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libata-sff.c checks for legacy mode by testing if both primary
and secondary ports on a controller are in legacy mode and selects
legacy if either one is. However on some southbridge chips (e.g
AMD SB600/SB700) the secondary port is not wired, and when it is 
disabled by setting the disable bit in the PCI header it appears
as a fixed legacy port.
Prevent incorrect detection by not testing ports that are marked
as 'dummy'

Signed-off-by: Darren Stevens <darren@stevens-zone.net>
---

 v2: Changed to using 2 if statements instead of binary logic

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diff --git a/drivers/ata/libata-sff.c b/drivers/ata/libata-sff.c
index 051b615..09bed5d 100644
--- a/drivers/ata/libata-sff.c
+++ b/drivers/ata/libata-sff.c
@@ -2427,11 +2427,21 @@ int ata_pci_sff_activate_host(struct ata_host *host,
 		return rc;
 
 	if ((pdev->class >> 8) == PCI_CLASS_STORAGE_IDE) {
-		u8 tmp8, mask;
+		u8 tmp8, mask = 0;
 
-		/* TODO: What if one channel is in native mode ... */
+		/*
+		 * ATA spec says we should use legacy mode when one
+		 * port is in legacy mode, but disabled ports on some
+		 * PCI hosts appear as fixed legacy ports, e.g SB600/700
+		 * on which the secondary port is not wired, so
+		 * ignore ports that are marked as 'dummy' during
+		 * this check
+		 */
 		pci_read_config_byte(pdev, PCI_CLASS_PROG, &tmp8);
-		mask = (1 << 2) | (1 << 0);
+		if (! ata_port_is_dummy(host->ports[1]))
+			mask = mask | (1 << 2);
+		if (! ata_port_is_dummy(host->ports[0]))
+			mask = mask | (1 << 0);
 		if ((tmp8 & mask) != mask)
 			legacy_mode = 1;
 	}