[PATCH] gpiolib: handle gpio-hogs only once

[Daniel Drake <dan@reactivated.net>]

Commit d1d564ec49929 ("gpio: move hogs into GPIO core") introduced a
behaviour change that breaks boot on Raspberry Pi 5 when using the
firmware-supplied device tree:

  gpiochip_add_data_with_key: GPIOs 544..575
    (/soc@107c000000/gpio@7d517c00) failed to register, -22
  brcmstb-gpio 107d517c00.gpio: Could not add gpiochip for bank 1
  brcmstb-gpio 107d517c00.gpio: probe with driver brcmstb-gpio failed
    with error -22

gpio-brcmstb registers two gpio_chips against the device tree
node gpio@7d517c00, one for each bank. The firmware-supplied DT includes
a gpio-hog on RP1 RUN, and this gpio-hog is attempted to be applied to
*both* gpio_chips. This succeeds against bank 0 (which hosts the GPIO)
and fails for bank 1 (which does not).

In the previous implementation, failures to apply gpio-hogs were
quietly ignored. In the new code, the error code propagates and causes
probe to fail.

Closely approximate the previous behaviour by ensuring that each
gpio-hog is processed only once. The handling of gpio-hogs on a DT node
with multiple gpio_chips remains a bit incomplete/unclear, but this at
least retains the ability to apply hogs to the first gpio_chip per node.

Signed-off-by: Daniel Drake <dan@reactivated.net>
---
 drivers/gpio/gpiolib.c | 5 +++++
 1 file changed, 5 insertions(+)

This bug is only exposed by the firmware-provided DT that has the
gpio-hog. The DT shipped in the mainline kernel does not have the hog
here. I'm not sure to what extent Linux cares about supporting the
RPi-downstream firmware DT.

I'm also happy to consider other approaches. This multi-gpiochip setup is
a bit weird and gpio-brcmstb could perhaps be converted to register only a
single gpio_chip covering all banks. I verified that the other drivers
that obviously follow this same multiple-gpiochip pattern
(pinctrl-amlogic-a4, pinctrl-st and pinctrl-stm32) do not seem to be used by
any board DTs that include gpio-hogs.

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index 1e6dce430dca..fc4dacee0a84 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -1031,6 +1031,11 @@ static int gpiochip_hog_lines(struct gpio_chip *gc)
 		if (!fwnode_property_present(fwnode, "gpio-hog"))
 			continue;
 
+		/* The hog may have been handled by another gpio_chip on the same fwnode */
+		if (is_of_node(fwnode) &&
+		    of_node_check_flag(to_of_node(fwnode), OF_POPULATED))
+			continue;
+
 		ret = gpiochip_add_hog(gc, fwnode);
 		if (ret)
 			return ret;
-- 
2.54.0