libata-sff: Don't try and activate channels which are not in use

diff -u --new-file --recursive --exclude-from /usr/src/exclude linux.vanilla-2.6.20-rc3-mm1/drivers/ata/libata-sff.c linux-2.6.20-rc3-mm1/drivers/ata/libata-sff.c
@@ -831,6 +831,21 @@
 }
 
 #ifdef CONFIG_PCI
+
+static int ata_resources_present(struct pci_dev *pdev, int port)
+{
+	int i;
+	
+	/* Check the PCI resources for this channel are enabled */
+	port = port * 2;
+	for (i = 0; i < 2; i ++) {
+		if (pci_resource_start(pdev, port + i) == 0 ||
+			pci_resource_len(pdev, port + i) == 0)
+		return 0;
+	}
+	return 1;
+}
+		
 /**
  *	ata_pci_init_native_mode - Initialize native-mode driver
  *	@pdev:  pci device to be initialized

@@ -862,6 +877,13 @@
 
 	probe_ent->irq = pdev->irq;
 	probe_ent->irq_flags = IRQF_SHARED;
+	
+	/* Discard disabled ports. Some controllers show their
+	   unused channels this way */
+	if (ata_resources_present(pdev, 0) == 0)
+		ports &= ~ATA_PORT_PRIMARY;
+	if (ata_resources_present(pdev, 1) == 0)
+		ports &= ~ATA_PORT_SECONDARY;
 
 	if (ports & ATA_PORT_PRIMARY) {
 		probe_ent->port[p].cmd_addr = pci_resource_start(pdev, 0);