Re: [PATCH v4 6/8] backlight: led-backlight: add devlink to supplier LEDs

Hi Luca,

On Mon, 2025-05-12 at 13:39 +0200, Alexander Sverdlin wrote:

quoted

led-backlight is a consumer of one or multiple LED class devices, but no
devlink is created for such supplier-producer relationship. One consequence
is that removal ordered is not correctly enforced.

Issues happen for example with the following sections in a device tree
overlay:

    // An LED driver chip
    pca9632@62 {
        compatible = "nxp,pca9632";
        reg = <0x62>;

	// ...

        addon_led_pwm: led-pwm@3 {
            reg = <3>;
            label = "addon:led:pwm";
        };
    };

    backlight-addon {
        compatible = "led-backlight";
        leds = <&addon_led_pwm>;
        brightness-levels = <255>;
        default-brightness-level = <255>;
    };

On removal of the above overlay, the LED driver can be removed before the
backlight device, resulting in:

    Unable to handle kernel NULL pointer dereference at virtual address 0000000000000010
    ...
    Call trace:
     led_put+0xe0/0x140
     devm_led_release+0x6c/0x98

Fix by adding a devlink between the consuming led-backlight device and the
supplying LED device.

Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>

I've tested the patch wit LP8864 LED as a provider for led_bl, removing the
underlying I2C bus. The patch avoids the crash for me (by removing led_bl device as well),
thanks for fixing it!

Tested-by: Alexander Sverdlin <alexander.sverdlin@siemens.com>

Would it make sense to add

Fixes: ae232e45acf9 ("backlight: add led-backlight driver")

?

-- 
Alexander Sverdlin
Siemens AG
www.siemens.com