[RFC/RFT PATCH] gpiolib: reverse-assign the fwnode to struct gpio_chip

[Bartosz Golaszewski <brgl@xxxxxxxx>]

From: Bartosz Golaszewski <bartosz.golaszewski@xxxxxxxxxx>

struct gpio_chip is not only used to carry the information needed to
set-up a GPIO device but is also used in all GPIOLIB callbacks and is
passed to the matching functions of lookup helpers.

In that last case, it is currently impossible to match a GPIO device by
fwnode unless it was explicitly assigned to the chip in the provider
code. If the fwnode is taken from the parent device, the pointer in
struct gpio_chip will remain NULL.

If we have a parent device but gc->fwnode was not assigned by the
provider, let's assign it ourselves so that lookup by fwnode can work in
all cases.

Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@xxxxxxxxxx>
---
This is something that Dipen reported with one of the tegra drivers where
a GPIO lookup by fwnode does not work because the fwnode pointer in struct
gpio_chip is NULL. This patch addresses this use-case.

 drivers/gpio/gpiolib.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index 191f9c87b4d0..a0e3d255fb73 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -782,6 +782,7 @@ int gpiochip_add_data_with_key(struct gpio_chip *gc, void *data,
 			       struct lock_class_key *lock_key,
 			       struct lock_class_key *request_key)
 {
+	struct fwnode_handle *parent_fwnode;
 	struct gpio_device *gdev;
 	unsigned long flags;
 	unsigned int i;
@@ -806,10 +807,13 @@ int gpiochip_add_data_with_key(struct gpio_chip *gc, void *data,
 	 * If the calling driver did not initialize firmware node,
 	 * do it here using the parent device, if any.
 	 */
-	if (gc->fwnode)
+	if (gc->fwnode) {
 		device_set_node(&gdev->dev, gc->fwnode);
-	else if (gc->parent)
-		device_set_node(&gdev->dev, dev_fwnode(gc->parent));
+	} else if (gc->parent) {
+		parent_fwnode = dev_fwnode(gc->parent);
+		device_set_node(&gdev->dev, parent_fwnode);
+		gc->fwnode = parent_fwnode;
+	}
 
 	gdev->id = ida_alloc(&gpio_ida, GFP_KERNEL);
 	if (gdev->id < 0) {
-- 
2.39.2