gpiolib: allow line names from device props to override driver names

Some GPIO providers set names for GPIO lines that match the names of
the pins on the SoC, or variations on that theme. These names are
generic more often that not, such as pioC12 in the at91 case. These
generic names block the possibility to set more useful GPIO line
names with device properties (i.e. gpio-line-names).

Allow overriding a generic name given by the GPIO driver if there is
a name given to the GPIO line using device properties, but leave the
generic name alone if no better name is available.

However, there is a risk. If user space is depending on the above
mentioned fixed GPIO names, AND there are device properties that
previously did not reach the surface, the name change might cause
regressions. But hopefully this stays below the radar...

Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Tested-by: Alexander Dahl <ada@thorsis.com>
Signed-off-by: Peter Rosin <peda@axentia.se>
Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>
Signed-off-by: Valentin Caron <valentin.caron@foss.st.com>
Change-Id: I26f7f2e1dcc49a7496da0d36ee526a4594189890
Reviewed-on: https://gerrit.st.com/c/mpu/oe/st/linux-stm32/+/271951
Reviewed-by: CITOOLS <MDG-smet-aci-reviews@list.st.com>
Reviewed-by: CIBUILD <MDG-smet-aci-builds@list.st.com>
Reviewed-by: Amelie DELAUNAY <amelie.delaunay@foss.st.com>
Reviewed-by: Antonio Maria BORNEO <antonio.borneo@st.com>
Reviewed-by: Eric FOURMONT <eric.fourmont-ext@st.com>
Domain-Review: Amelie DELAUNAY <amelie.delaunay@foss.st.com>

Author: peda-r

drivers/gpio/gpiolib.c

@@ -422,8 +422,16 @@ static int devprop_gpiochip_set_names(struct gpio_chip *chip)
 	if (count > chip->ngpio)
 		count = chip->ngpio;
 
-	for (i = 0; i < count; i++)
-		gdev->descs[i].name = names[chip->offset + i];
+	for (i = 0; i < count; i++) {
+		/*
+		 * Allow overriding "fixed" names provided by the GPIO
+		 * provider. The "fixed" names are more often than not
+		 * generic and less informative than the names given in
+		 * device properties.
+		 */
+		if (names[chip->offset + i] && names[chip->offset + i][0])
+			gdev->descs[i].name = names[chip->offset + i];
+	}
 
 	kfree(names);
 
@@ -708,10 +716,12 @@ int gpiochip_add_data_with_key(struct gpio_chip *gc, void *data,
 	INIT_LIST_HEAD(&gdev->pin_ranges);
 #endif
 
-	if (gc->names)
+	if (gc->names) {
 		ret = gpiochip_set_desc_names(gc);
-	else
-		ret = devprop_gpiochip_set_names(gc);
+		if (ret)
+			goto err_remove_from_list;
+	}
+	ret = devprop_gpiochip_set_names(gc);
 	if (ret)
 		goto err_remove_from_list;