pata_serverworks: Fix problem with some drive combinations

The driver used the channel not the device number for deciding where to
load some timing parameters. Also change so that we clear the UDMA field
as the old driver did. Not believed neccessary but does no harm.
Signed-off-by: Alan Cox <alan@redhat.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>

drivers/ata/pata_serverworks.c

@@ -274,28 +274,27 @@ static void serverworks_set_dmamode(struct ata_port *ap, struct ata_device *adev
 {
 	static const u8 dma_mode[] = { 0x77, 0x21, 0x20 };
 	int offset = 1 + 2 * ap->port_no - adev->devno;
-	int devbits = (2 * ap->port_no + adev->devno);
+	int devbits = 2 * ap->port_no + adev->devno;
 	u8 ultra;
 	u8 ultra_cfg;
 	struct pci_dev *pdev = to_pci_dev(ap->host->dev);
 
 	pci_read_config_byte(pdev, 0x54, &ultra_cfg);
+	pci_read_config_byte(pdev, 0x56 + ap->port_no, &ultra);
+	ultra &= ~(0x0F << (adev->devno * 4));
 
 	if (adev->dma_mode >= XFER_UDMA_0) {
 		pci_write_config_byte(pdev, 0x44 + offset,  0x20);
 
-		pci_read_config_byte(pdev, 0x56 + ap->port_no, &ultra);
-		ultra &= ~(0x0F << (ap->port_no * 4));
 		ultra |= (adev->dma_mode - XFER_UDMA_0)
-					<< (ap->port_no * 4);
-		pci_write_config_byte(pdev, 0x56 + ap->port_no, ultra);
-
+					<< (adev->devno * 4);
 		ultra_cfg |=  (1 << devbits);
 	} else {
 		pci_write_config_byte(pdev, 0x44 + offset,
 			dma_mode[adev->dma_mode - XFER_MW_DMA_0]);
 		ultra_cfg &= ~(1 << devbits);
 	}
+	pci_write_config_byte(pdev, 0x56 + ap->port_no, ultra);
 	pci_write_config_byte(pdev, 0x54, ultra_cfg);
 }