gpio: No NULL owner

BugLink: https://bugs.launchpad.net/bugs/1777389

commit 7d18f0a1 upstream.

Sometimes a GPIO is fetched with NULL as parent device, and
that is just fine. So under these circumstances, avoid using
dev_name() to provide a name for the GPIO line.
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Cc: Daniel Rosenberg <drosen@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Juerg Haefliger <juergh@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

drivers/gpio/gpiolib.c

@@ -2186,6 +2186,8 @@ struct gpio_desc *__must_check gpiod_get_index(struct device *dev,
 	struct gpio_desc *desc = NULL;
 	int status;
 	enum gpio_lookup_flags lookupflags = 0;
+	/* Maybe we have a device name, maybe not */
+	const char *devname = dev ? dev_name(dev) : "?";
 
 	dev_dbg(dev, "GPIO lookup for consumer %s\n", con_id);
 
@@ -2214,8 +2216,11 @@ struct gpio_desc *__must_check gpiod_get_index(struct device *dev,
 		return desc;
 	}
 
-	/* If a connection label was passed use that, else use the device name as label */
-	status = gpiod_request(desc, con_id ? con_id : dev_name(dev));
+	/*
+	 * If a connection label was passed use that, else attempt to use
+	 * the device name as label
+	 */
+	status = gpiod_request(desc, con_id ? con_id : devname);
 	if (status < 0)
 		return ERR_PTR(status);