gpiolib: Keep returning EPROBE_DEFER when we should

Commits c8582339 ("gpio: of: Support SPI nonstandard GPIO properties")
and 6a537d48 ("gpio: of: Support regulator nonstandard GPIO
properties") have introduced a regression in the way error codes from
of_get_named_gpiod_flags are handled.

Previously, those errors codes were returned immediately, but the two
commits mentioned above are now overwriting the error pointer, meaning that
whatever value has been returned will be dropped in favor of whatever the
two new functions will return.

This might not be a big deal except for EPROBE_DEFER, on which GPIOlib
customers will depend on, and that will now be returned as an hard error
which means that they will not probe anymore, instead of gently deferring
their probe.

Since EPROBE_DEFER basically means that we have found a valid property but
there was no GPIO controller registered to handle it, fix this issues by
returning it as soon as we encounter it.

Fixes: c8582339 ("gpio: of: Support SPI nonstandard GPIO properties")
Fixes: 6a537d48 ("gpio: of: Support regulator nonstandard GPIO properties")
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
[Fold in fix to the fix]
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/gpio/gpiolib-of.c

@@ -241,6 +241,19 @@ struct gpio_desc *of_find_gpio(struct device *dev, const char *con_id,
 
 		desc = of_get_named_gpiod_flags(dev->of_node, prop_name, idx,
 						&of_flags);
+		/*
+		 * -EPROBE_DEFER in our case means that we found a
+		 * valid GPIO property, but no controller has been
+		 * registered so far.
+		 *
+		 * This means we don't need to look any further for
+		 * alternate name conventions, and we should really
+		 * preserve the return code for our user to be able to
+		 * retry probing later.
+		 */
+		if (IS_ERR(desc) && PTR_ERR(desc) == -EPROBE_DEFER)
+			return desc;
+
 		if (!IS_ERR(desc) || (PTR_ERR(desc) != -ENOENT))
 			break;
 	}