[PATCH] gpiolib: Extend software-node support to support secondary software-nodes

[Hans de Goede <hansg@kernel.org>]

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 check to gpiod_find_by_fwnode() to try a software-node lookup on
the secondary fwnode if the GPIO was not found in the primary fwnode.

Fixes: e7f9ff5dc90c ("gpiolib: add support for software nodes")
Cc: stable@vger.kernel.org
Cc: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Hans de Goede <hansg@kernel.org>
---
I found this issue while testing "platform/x86: x86-android-tablets:
convert wm1502 devices to GPIO references":
https://lore.kernel.org/platform-driver-x86/20250810-x86-andoroid-tablet-v2-7-9c7a1b3c32b2@gmail.com/
which adds a software node with GPIO lookup info the a spi-10WM5102:00
device which has an ACPI fwnode as primary fwnode.
---
 drivers/gpio/gpiolib.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index 0d2b470a252e..b619fea498c8 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -4601,6 +4601,12 @@ static struct gpio_desc *gpiod_find_by_fwnode(struct fwnode_handle *fwnode,
 		desc = swnode_find_gpio(fwnode, con_id, idx, lookupflags);
 	}
 
+	if (desc == ERR_PTR(-ENOENT) && fwnode && is_software_node(fwnode->secondary)) {
+		dev_dbg(consumer, "using secondary-swnode '%pfw' for '%s' GPIO lookup\n",
+			fwnode->secondary, name);
+		desc = swnode_find_gpio(fwnode->secondary, con_id, idx, lookupflags);
+	}
+
 	return desc;
 }
 
-- 
2.51.0