gpio: Fix return value mismatch of function gpiod_get_from_of_node()

In case the requested gpio property is not found in the device tree, some
callers of gpiod_get_from_of_node() expect a return value of NULL, others
expect -ENOENT.
In particular devm_fwnode_get_index_gpiod_from_child() expects -ENOENT.
Currently it gets a NULL, which breaks the loop that tries all
gpio_suffixes. The result is that a gpio property is not found, even
though it is there.

This patch changes gpiod_get_from_of_node() to return -ENOENT instead
of NULL when the requested gpio property is not found in the device
tree. Additionally it modifies all calling functions to properly
evaluate the return value.

Another approach would be to leave the return value of
gpiod_get_from_of_node() as is and fix the bug in
devm_fwnode_get_index_gpiod_from_child(). Other callers would still need
to be reworked. The effort would be the same as with the chosen solution.

Signed-off-by: Georg Waibel <[e-mail]>
Reviewed-by: Krzysztof Kozlowski <[e-mail]>
Reviewed-by: Linus Walleij <[e-mail]>
Signed-off-by: Mark Brown <[e-mail]>

drivers/gpio/gpiolib.c

···
  *
  * Returns:
  * On successful request the GPIO pin is configured in accordance with
- * provided @dflags. If the node does not have the requested GPIO
- * property, NULL is returned.
+ * provided @dflags.
  *
  * In case of error an ERR_PTR() is returned.
  */
···
 					index, &flags);
 
 	if (!desc || IS_ERR(desc)) {
-		/* If it is not there, just return NULL */
-		if (PTR_ERR(desc) == -ENOENT)
-			return NULL;
 		return desc;
 	}
 

drivers/regulator/da9211-regulator.c

···
 				  0,
 				  GPIOD_OUT_HIGH | GPIOD_FLAGS_BIT_NONEXCLUSIVE,
 				  "da9211-enable");
+		if (IS_ERR(pdata->gpiod_ren[n]))
+			pdata->gpiod_ren[n] = NULL;
 		n++;
 	}
 

drivers/regulator/s2mps11.c

···
 				0,
 				GPIOD_OUT_HIGH | GPIOD_FLAGS_BIT_NONEXCLUSIVE,
 				"s2mps11-regulator");
-		if (IS_ERR(gpio[reg])) {
+		if (PTR_ERR(gpio[reg]) == -ENOENT)
+			gpio[reg] = NULL;
+		else if (IS_ERR(gpio[reg])) {
 			dev_err(&pdev->dev, "Failed to get control GPIO for %d/%s\n",
 				reg, rdata[reg].name);
 			continue;

drivers/regulator/s5m8767.c

···
 			0,
 			GPIOD_OUT_HIGH | GPIOD_FLAGS_BIT_NONEXCLUSIVE,
 			"s5m8767");
-		if (IS_ERR(rdata->ext_control_gpiod))
+		if (PTR_ERR(rdata->ext_control_gpiod) == -ENOENT)
+			rdata->ext_control_gpiod = NULL;
+		else if (IS_ERR(rdata->ext_control_gpiod))
 			return PTR_ERR(rdata->ext_control_gpiod);
 
 		rdata->id = i;

drivers/regulator/tps65090-regulator.c

···
 								    "dcdc-ext-control-gpios", 0,
 								    gflags,
 								    "tps65090");
-			if (IS_ERR(rpdata->gpiod))
-				return ERR_CAST(rpdata->gpiod);
-			if (!rpdata->gpiod)
+			if (PTR_ERR(rpdata->gpiod) == -ENOENT) {
 				dev_err(&pdev->dev,
 					"could not find DCDC external control GPIO\n");
+				rpdata->gpiod = NULL;
+			} else if (IS_ERR(rpdata->gpiod))
+				return ERR_CAST(rpdata->gpiod);
 		}
 
 		if (of_property_read_u32(tps65090_matches[idx].of_node,