ahci: work around ATI SB600 h/w quirk

This addresses the recent ATI SB600 errata, where the hardware does
not like 256-length PRD entries during FPDMA (aka NCQ).

It hurts performance on SB600, but it is more important to get a
correct patch eliminating the data corruption/lockups, and then later
on tune for performance.

We simply limit each command to a maximum of 255 sectors, on SB600.
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>

drivers/ata/ahci.c

@@ -186,6 +186,7 @@ enum {
 	AHCI_HFLAG_NO_MSI		= (1 << 5), /* no PCI MSI */
 	AHCI_HFLAG_NO_PMP		= (1 << 6), /* no PMP */
 	AHCI_HFLAG_NO_HOTPLUG		= (1 << 7), /* ignore PxSERR.DIAG.N */
+	AHCI_HFLAG_SECT255		= (1 << 8), /* max 255 sectors */
 
 	/* ap->flags bits */
 
@@ -255,6 +256,7 @@ static void ahci_vt8251_error_handler(struct ata_port *ap);
 static void ahci_p5wdh_error_handler(struct ata_port *ap);
 static void ahci_post_internal_cmd(struct ata_queued_cmd *qc);
 static int ahci_port_resume(struct ata_port *ap);
+static void ahci_dev_config(struct ata_device *dev);
 static unsigned int ahci_fill_sg(struct ata_queued_cmd *qc, void *cmd_tbl);
 static void ahci_fill_cmd_slot(struct ahci_port_priv *pp, unsigned int tag,
 			       u32 opts);
@@ -294,6 +296,8 @@ static const struct ata_port_operations ahci_ops = {
 	.check_altstatus	= ahci_check_status,
 	.dev_select		= ata_noop_dev_select,
 
+	.dev_config		= ahci_dev_config,
+
 	.tf_read		= ahci_tf_read,
 
 	.qc_defer		= sata_pmp_qc_defer_cmd_switch,
@@ -425,7 +429,7 @@ static const struct ata_port_info ahci_port_info[] = {
 	/* board_ahci_sb600 */
 	{
 		AHCI_HFLAGS	(AHCI_HFLAG_IGN_SERR_INTERNAL |
-				 AHCI_HFLAG_32BIT_ONLY | AHCI_HFLAG_NO_PMP),
+				 AHCI_HFLAG_SECT255 | AHCI_HFLAG_NO_PMP),
 		.flags		= AHCI_FLAG_COMMON,
 		.link_flags	= AHCI_LFLAG_COMMON,
 		.pio_mask	= 0x1f, /* pio0-4 */
@@ -1176,6 +1180,14 @@ static void ahci_init_controller(struct ata_host *host)
 	VPRINTK("HOST_CTL 0x%x\n", tmp);
 }
 
+static void ahci_dev_config(struct ata_device *dev)
+{
+	struct ahci_host_priv *hpriv = dev->link->ap->host->private_data;
+
+	if (hpriv->flags & AHCI_HFLAG_SECT255)
+		dev->max_sectors = 255;
+}
+
 static unsigned int ahci_dev_classify(struct ata_port *ap)
 {
 	void __iomem *port_mmio = ahci_port_base(ap);