[PATCH v2] gpio: swnode: restore the swnode-name-against-chip-label matching

[Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>]

Using the remote firmware node for software node lookup is the right
thing to do. The GPIO controller we want to resolve should have the
software node we scooped out of the reference attached to it. However,
there are existing users who abuse the software node API by creating
dummy swnodes whose name is set to the expected label string of the GPIO
controller whose pins they want to control and use them in their local
swnode references as GPIO properties.

This used to work when we compared the software node's name to the
chip's label. When we switched to using a real fwnode lookup, these
users broke down because the firmware nodes in question were never
attached to the controllers they were looking for.

Restore the label matching as a fallback to fix the broken users but add
a big FIXME urging for a better solution.

Cc: stable@vger.kernel.org # v6.18, v6.19
Fixes: 216c12047571 ("gpio: swnode: allow referencing GPIO chips by firmware nodes")
Link: https://lore.kernel.org/all/aYkdKfP5fg6iywgr@jekhomev/
Acked-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>
---
Changes in v2:
- check if gdev_node and gdev_node->name are not NULL before trying to
  match the label (Hans & Dan)
- use the right link
- collect tags

 drivers/gpio/gpiolib-swnode.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/drivers/gpio/gpiolib-swnode.c b/drivers/gpio/gpiolib-swnode.c
index 21478b45c127d..0d7f3f09a0b4b 100644
--- a/drivers/gpio/gpiolib-swnode.c
+++ b/drivers/gpio/gpiolib-swnode.c
@@ -42,6 +42,25 @@ static struct gpio_device *swnode_get_gpio_device(struct fwnode_handle *fwnode)
 
 fwnode_lookup:
 	gdev = gpio_device_find_by_fwnode(fwnode);
+	if (!gdev && gdev_node && gdev_node->name)
+		/*
+		 * FIXME: We shouldn't need to compare the GPIO controller's
+		 * label against the software node that is supposedly attached
+		 * to it. However there are currently GPIO users that - knowing
+		 * the expected label of the GPIO chip whose pins they want to
+		 * control - set up dummy software nodes named after those GPIO
+		 * controllers, which aren't actually attached to them. In this
+		 * case gpio_device_find_by_fwnode() will fail as no device on
+		 * the GPIO bus is actually associated with the fwnode we're
+		 * looking for.
+		 *
+		 * As a fallback: continue checking the label if we have no
+		 * match. However, the situation described above is an abuse
+		 * of the software node API and should be phased out and the
+		 * following line - eventually removed.
+		 */
+		gdev = gpio_device_find_by_label(gdev_node->name);
+
 	return gdev ?: ERR_PTR(-EPROBE_DEFER);
 }
 
-- 
2.47.3