ahci: disable SNotification capability for ich8

I obseved there is a sata_async_notification() for every ahci
interrupt. But the async notification does nothing (this is hard
disk drive and no pmp). This cause cpu wastes some time on sntf
register access.

It appears ICH AHCI doesn't support SNotification register, but the
controller reports it does. After quirking it, the async notification
disappears.

PS. it appears all ICH don't support SNotification register from ICH
manual, don't know if we need quirk all ICH. I don't have machines
with all kinds of ICH.

Signed-off-by: Shaohua Li <shaohua.li@intel.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>

drivers/ata/ahci.c

@@ -113,6 +113,7 @@ enum {
 	board_ahci_mcp65	= 6,
 	board_ahci_nopmp	= 7,
 	board_ahci_yesncq	= 8,
+	board_ahci_nosntf	= 9,
 
 	/* global controller registers */
 	HOST_CAP		= 0x00, /* host capabilities */
@@ -235,6 +236,7 @@ enum {
 	AHCI_HFLAG_NO_SUSPEND		= (1 << 10), /* don't suspend */
 	AHCI_HFLAG_SRST_TOUT_IS_OFFLINE	= (1 << 11), /* treat SRST timeout as
 							link offline */
+	AHCI_HFLAG_NO_SNTF		= (1 << 12), /* no sntf */
 
 	/* ap->flags bits */
 
@@ -508,14 +510,22 @@ static const struct ata_port_info ahci_port_info[] = {
 		.udma_mask	= ATA_UDMA6,
 		.port_ops	= &ahci_ops,
 	},
-	/* board_ahci_yesncq */
+	[board_ahci_yesncq] =
 	{
 		AHCI_HFLAGS	(AHCI_HFLAG_YES_NCQ),
 		.flags		= AHCI_FLAG_COMMON,
 		.pio_mask	= ATA_PIO4,
 		.udma_mask	= ATA_UDMA6,
 		.port_ops	= &ahci_ops,
 	},
+	[board_ahci_nosntf] =
+	{
+		AHCI_HFLAGS	(AHCI_HFLAG_NO_SNTF),
+		.flags		= AHCI_FLAG_COMMON,
+		.pio_mask	= ATA_PIO4,
+		.udma_mask	= ATA_UDMA6,
+		.port_ops	= &ahci_ops,
+	},
 };
 
 static const struct pci_device_id ahci_pci_tbl[] = {
@@ -531,7 +541,7 @@ static const struct pci_device_id ahci_pci_tbl[] = {
 	{ PCI_VDEVICE(INTEL, 0x2683), board_ahci }, /* ESB2 */
 	{ PCI_VDEVICE(INTEL, 0x27c6), board_ahci }, /* ICH7-M DH */
 	{ PCI_VDEVICE(INTEL, 0x2821), board_ahci }, /* ICH8 */
-	{ PCI_VDEVICE(INTEL, 0x2822), board_ahci }, /* ICH8 */
+	{ PCI_VDEVICE(INTEL, 0x2822), board_ahci_nosntf }, /* ICH8 */
 	{ PCI_VDEVICE(INTEL, 0x2824), board_ahci }, /* ICH8 */
 	{ PCI_VDEVICE(INTEL, 0x2829), board_ahci }, /* ICH8M */
 	{ PCI_VDEVICE(INTEL, 0x282a), board_ahci }, /* ICH8M */
@@ -849,6 +859,12 @@ static void ahci_save_initial_config(struct pci_dev *pdev,
 		cap &= ~HOST_CAP_PMP;
 	}
 
+	if ((cap & HOST_CAP_SNTF) && (hpriv->flags & AHCI_HFLAG_NO_SNTF)) {
+		dev_printk(KERN_INFO, &pdev->dev,
+			   "controller can't do SNTF, turning off CAP_SNTF\n");
+		cap &= ~HOST_CAP_SNTF;
+	}
+
 	if (pdev->vendor == PCI_VENDOR_ID_JMICRON && pdev->device == 0x2361 &&
 	    port_map != 1) {
 		dev_printk(KERN_INFO, &pdev->dev,