ahci: Add check for device presence (PCIe hot unplug) in ahci_stop_engine()

Exit directly with ENODEV, if the AHCI controller is not available
anymore. Otherwise a delay of 500ms for each port is added to the remove
function while trying to issue a command on the non-existent controller.
Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Tejun Heo <tj@kernel.org>

drivers/ata/libahci.c

@@ -665,6 +665,16 @@ int ahci_stop_engine(struct ata_port *ap)
 	if ((tmp & (PORT_CMD_START | PORT_CMD_LIST_ON)) == 0)
 		return 0;
 
+	/*
+	 * Don't try to issue commands but return with ENODEV if the
+	 * AHCI controller not available anymore (e.g. due to PCIe hot
+	 * unplugging). Otherwise a 500ms delay for each port is added.
+	 */
+	if (tmp == 0xffffffff) {
+		dev_err(ap->host->dev, "AHCI controller unavailable!\n");
+		return -ENODEV;
+	}
+
 	/* setting HBA to idle */
 	tmp &= ~PORT_CMD_START;
 	writel(tmp, port_mmio + PORT_CMD);