[libata] ahci: Restore SB600 SATA controller 64 bit DMA

Community reported one SB600 SATA issue(BZ #9412), which led to 64 bit
DMA disablement for all SB600 revisions by driver maintainers with
commits c7a42156 and
4cde32fc.

But the root cause is ASUS M2A-VM system BIOS bug in old revisions
like 0901, while forcing into 32bit DMA happens to work as workaround.
Now it's time to withdraw 4cde32fc
so as to restore the SB600 SATA 64bit DMA capability.
This patch is also adding the workaround for M2A-VM old BIOS revisions,
but users are suggested to upgrade their system BIOS to the latest one
if they meet this issue.
Signed-off-by: Shane Huang <shane.huang@amd.com>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>

drivers/ata/ahci.c

@@ -431,8 +431,7 @@ 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_MSI |
-				 AHCI_HFLAG_SECT255),
+				 AHCI_HFLAG_NO_MSI | AHCI_HFLAG_SECT255),
 		.flags		= AHCI_FLAG_COMMON,
 		.pio_mask	= ATA_PIO4,
 		.udma_mask	= ATA_UDMA6,
@@ -2585,6 +2584,51 @@ static void ahci_p5wdh_workaround(struct ata_host *host)
 	}
 }
 
+/*
+ * SB600 ahci controller on ASUS M2A-VM can't do 64bit DMA with older
+ * BIOS.  The oldest version known to be broken is 0901 and working is
+ * 1501 which was released on 2007-10-26.  Force 32bit DMA on anything
+ * older than 1501.  Please read bko#9412 for more info.
+ */
+static bool ahci_asus_m2a_vm_32bit_only(struct pci_dev *pdev)
+{
+	static const struct dmi_system_id sysids[] = {
+		{
+			.ident = "ASUS M2A-VM",
+			.matches = {
+				DMI_MATCH(DMI_BOARD_VENDOR,
+					  "ASUSTeK Computer INC."),
+				DMI_MATCH(DMI_BOARD_NAME, "M2A-VM"),
+			},
+		},
+		{ }
+	};
+	const char *cutoff_mmdd = "10/26";
+	const char *date;
+	int year;
+
+	if (pdev->bus->number != 0 || pdev->devfn != PCI_DEVFN(0x12, 0) ||
+	    !dmi_check_system(sysids))
+		return false;
+
+	/*
+	 * Argh.... both version and date are free form strings.
+	 * Let's hope they're using the same date format across
+	 * different versions.
+	 */
+	date = dmi_get_system_info(DMI_BIOS_DATE);
+	year = dmi_get_year(DMI_BIOS_DATE);
+	if (date && strlen(date) >= 10 && date[2] == '/' && date[5] == '/' &&
+	    (year > 2007 ||
+	     (year == 2007 && strncmp(date, cutoff_mmdd, 5) >= 0)))
+		return false;
+
+	dev_printk(KERN_WARNING, &pdev->dev, "ASUS M2A-VM: BIOS too old, "
+		   "forcing 32bit DMA, update BIOS\n");
+
+	return true;
+}
+
 static bool ahci_broken_system_poweroff(struct pci_dev *pdev)
 {
 	static const struct dmi_system_id broken_systems[] = {
@@ -2745,6 +2789,10 @@ static int ahci_init_one(struct pci_dev *pdev, const struct pci_device_id *ent)
 	if (board_id == board_ahci_sb700 && pdev->revision >= 0x40)
 		hpriv->flags &= ~AHCI_HFLAG_IGN_SERR_INTERNAL;
 
+	/* apply ASUS M2A_VM quirk */
+	if (ahci_asus_m2a_vm_32bit_only(pdev))
+		hpriv->flags |= AHCI_HFLAG_32BIT_ONLY;
+
 	if (!(hpriv->flags & AHCI_HFLAG_NO_MSI))
 		pci_enable_msi(pdev);
 

drivers/firmware/dmi_scan.c

@@ -596,6 +596,7 @@ int dmi_get_year(int field)
 
 	return year;
 }
+EXPORT_SYMBOL(dmi_get_year);
 
 /**
  *	dmi_walk - Walk the DMI table and get called back for every record