ahci: Acer SA5-271 SSD Not Detected Fix

commit 8bfd1743 upstream.

(Correction in this resend: fixed function name acer_sa5_271_workaround; fixed
 the always-true condition in the function; fixed description.)

On the Acer Switch Alpha 12 (model number: SA5-271), the internal SSD may not
get detected because the port_map and CAP.nr_ports combination causes the driver
to skip the port that is actually connected to the SSD. More specifically,
either all SATA ports are identified as DUMMY, or all ports get ``link down''
and never get up again.

This problem occurs occasionally. When this problem occurs, CAP may hold a
value of 0xC734FF00 or 0xC734FF01 and port_map may hold a value of 0x00 or 0x01.
When this problem does not occur, CAP holds a value of 0xC734FF02 and port_map
may hold a value of 0x07. Overriding the CAP value to 0xC734FF02 and port_map to
0x7 significantly reduces the occurrence of this problem.

Link: https://bugzilla.kernel.org/attachment.cgi?id=253091Signed-off-by: Sui Chen <suichen6@gmail.com>
Tested-by: Damian Ivanov <damianatorrpm@gmail.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/ata/ahci.c

@@ -1313,6 +1313,40 @@ static inline void ahci_gtf_filter_workaround(struct ata_host *host)
 {}
 #endif
 
+/*
+ * On the Acer Aspire Switch Alpha 12, sometimes all SATA ports are detected
+ * as DUMMY, or detected but eventually get a "link down" and never get up
+ * again. When this happens, CAP.NP may hold a value of 0x00 or 0x01, and the
+ * port_map may hold a value of 0x00.
+ *
+ * Overriding CAP.NP to 0x02 and the port_map to 0x7 will reveal all 3 ports
+ * and can significantly reduce the occurrence of the problem.
+ *
+ * https://bugzilla.kernel.org/show_bug.cgi?id=189471
+ */
+static void acer_sa5_271_workaround(struct ahci_host_priv *hpriv,
+				    struct pci_dev *pdev)
+{
+	static const struct dmi_system_id sysids[] = {
+		{
+			.ident = "Acer Switch Alpha 12",
+			.matches = {
+				DMI_MATCH(DMI_SYS_VENDOR, "Acer"),
+				DMI_MATCH(DMI_PRODUCT_NAME, "Switch SA5-271")
+			},
+		},
+		{ }
+	};
+
+	if (dmi_check_system(sysids)) {
+		dev_info(&pdev->dev, "enabling Acer Switch Alpha 12 workaround\n");
+		if ((hpriv->saved_cap & 0xC734FF00) == 0xC734FF00) {
+			hpriv->port_map = 0x7;
+			hpriv->cap = 0xC734FF02;
+		}
+	}
+}
+
 static int ahci_init_interrupts(struct pci_dev *pdev, unsigned int n_ports,
 				struct ahci_host_priv *hpriv)
 {
@@ -1565,6 +1599,10 @@ static int ahci_init_one(struct pci_dev *pdev, const struct pci_device_id *ent)
 			 "online status unreliable, applying workaround\n");
 	}
 
+
+	/* Acer SA5-271 workaround modifies private_data */
+	acer_sa5_271_workaround(hpriv, pdev);
+
 	/* CAP.NP sometimes indicate the index of the last enabled
 	 * port, at other times, that of the last possible port, so
 	 * determining the maximum port number requires looking at