gpiolib: Extend software-node support to support secondary software-nodes

When a software-node gets added to a device which already has another
fwnode as primary node it will become the secondary fwnode for that
device.

Currently if a software-node with GPIO properties ends up as the secondary
fwnode then gpiod_find_by_fwnode() will fail to find the GPIOs.

Add a new gpiod_fwnode_lookup() helper which falls back to calling
gpiod_find_by_fwnode() with the secondary fwnode if the GPIO was not
found in the primary fwnode.

Fixes: e7f9ff5 ("gpiolib: add support for software nodes")
Cc: stable@vger.kernel.org
Signed-off-by: Hans de Goede <hansg@kernel.org>
Reviewed-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Link: https://lore.kernel.org/r/20250920200955.20403-1-hansg@kernel.org
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

Author: Hans de Goede

drivers/gpio/gpiolib.c

@@ -4604,6 +4604,23 @@ static struct gpio_desc *gpiod_find_by_fwnode(struct fwnode_handle *fwnode,
 	return desc;
 }
 
+static struct gpio_desc *gpiod_fwnode_lookup(struct fwnode_handle *fwnode,
+					     struct device *consumer,
+					     const char *con_id,
+					     unsigned int idx,
+					     enum gpiod_flags *flags,
+					     unsigned long *lookupflags)
+{
+	struct gpio_desc *desc;
+
+	desc = gpiod_find_by_fwnode(fwnode, consumer, con_id, idx, flags, lookupflags);
+	if (gpiod_not_found(desc) && !IS_ERR_OR_NULL(fwnode))
+		desc = gpiod_find_by_fwnode(fwnode->secondary, consumer, con_id,
+					    idx, flags, lookupflags);
+
+	return desc;
+}
+
 struct gpio_desc *gpiod_find_and_request(struct device *consumer,
 					 struct fwnode_handle *fwnode,
 					 const char *con_id,
@@ -4622,8 +4639,8 @@ struct gpio_desc *gpiod_find_and_request(struct device *consumer,
 	int ret = 0;
 
 	scoped_guard(srcu, &gpio_devices_srcu) {
-		desc = gpiod_find_by_fwnode(fwnode, consumer, con_id, idx,
-					    &flags, &lookupflags);
+		desc = gpiod_fwnode_lookup(fwnode, consumer, con_id, idx,
+					   &flags, &lookupflags);
 		if (gpiod_not_found(desc) && platform_lookup_allowed) {
 			/*
 			 * Either we are not using DT or ACPI, or their lookup