diff --git a/drivers/ide/pci/cmd64x.c b/drivers/ide/pci/cmd64x.c
index f165bf1..63fd929 100644
--- a/drivers/ide/pci/cmd64x.c
+++ b/drivers/ide/pci/cmd64x.c
@@ -1,5 +1,5 @@
 /*
- * linux/drivers/ide/pci/cmd64x.c		Version 1.44	Mar 12, 2007
+ * linux/drivers/ide/pci/cmd64x.c		Version 1.45	Mar 14, 2007
  *
  * cmd64x.c: Enable interrupts at initialization time on Ultra/PCI machines.
  *           Due to massive hardware bugs, UltraDMA is only supported
@@ -684,42 +684,75 @@
 	hwif->drives[1].autodma = hwif->autodma;
 }
 
+static int __devinit init_setup_cmd64x(struct pci_dev *dev, ide_pci_device_t *d)
+{
+	return ide_setup_pci_device(dev, d);
+}
+
+static int __devinit init_setup_cmd646(struct pci_dev *dev, ide_pci_device_t *d)
+{
+	u8 rev = 0;
+
+	/*
+	 * The original PCI0646 didn't have the primary channel enable bit,
+	 * it appeared starting with PCI0646U (i.e. revision ID 3).
+	 */
+	pci_read_config_byte(dev, PCI_REVISION_ID, &rev);
+	if (rev < 3)
+		d->enablebits[0].reg = 0;
+
+	return ide_setup_pci_device(dev, d);
+}
+
 static ide_pci_device_t cmd64x_chipsets[] __devinitdata = {
 	{	/* 0 */
 		.name		= "CMD643",
+		.init_setup	= init_setup_cmd64x,
 		.init_chipset	= init_chipset_cmd64x,
 		.init_hwif	= init_hwif_cmd64x,
 		.channels	= 2,
 		.autodma	= AUTODMA,
+		.enablebits	= {{0x00,0x00,0x00}, {0x51,0x08,0x08}},
 		.bootable	= ON_BOARD,
 	},{	/* 1 */
 		.name		= "CMD646",
+		.init_setup	= init_setup_cmd646,
 		.init_chipset	= init_chipset_cmd64x,
 		.init_hwif	= init_hwif_cmd64x,
 		.channels	= 2,
 		.autodma	= AUTODMA,
-		.enablebits	= {{0x00,0x00,0x00}, {0x51,0x80,0x80}},
+		.enablebits	= {{0x51,0x04,0x04}, {0x51,0x08,0x08}},
 		.bootable	= ON_BOARD,
 	},{	/* 2 */
 		.name		= "CMD648",
+		.init_setup	= init_setup_cmd64x,
 		.init_chipset	= init_chipset_cmd64x,
 		.init_hwif	= init_hwif_cmd64x,
 		.channels	= 2,
 		.autodma	= AUTODMA,
+		.enablebits	= {{0x51,0x04,0x04}, {0x51,0x08,0x08}},
 		.bootable	= ON_BOARD,
 	},{	/* 3 */
 		.name		= "CMD649",
+		.init_setup	= init_setup_cmd64x,
 		.init_chipset	= init_chipset_cmd64x,
 		.init_hwif	= init_hwif_cmd64x,
 		.channels	= 2,
 		.autodma	= AUTODMA,
+		.enablebits	= {{0x51,0x04,0x04}, {0x51,0x08,0x08}},
 		.bootable	= ON_BOARD,
 	}
 };
 
+/*
+ * We may have to modify enablebits for PCI0646, so we'd better pass
+ * a local copy of the ide_pci_device_t structure down the call chain...
+ */
 static int __devinit cmd64x_init_one(struct pci_dev *dev, const struct pci_device_id *id)
 {
-	return ide_setup_pci_device(dev, &cmd64x_chipsets[id->driver_data]);
+	ide_pci_device_t d = cmd64x_chipsets[id->driver_data];
+
+	return d.init_setup(dev, &d);
 }
 
 static struct pci_device_id cmd64x_pci_tbl[] = {