diff --git a/drivers/ata/pata_serverworks.c b/drivers/ata/pata_serverworks.c
index df68806..8bed888 100644
--- a/drivers/ata/pata_serverworks.c
+++ b/drivers/ata/pata_serverworks.c
@@ -274,28 +274,27 @@
 {
 	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);
 }