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backlight: led-bl: Add devlink to supplier LEDs 

LED Backlight is a consumer of one or multiple LED class devices, but
devlink is currently unable to create correct supplier-producer links when
the supplier is a class device. It creates instead a link where the
supplier is the parent of the expected device.

One consequence is that removal order 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>;
    };

In this example, the devlink should be created between the backlight-addon
(consumer) and the pca9632@62 (supplier). Instead it is created between the
backlight-addon (consumer) and the parent of the pca9632@62, which is
typically the I2C bus adapter.

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

Another way to reproduce the bug without any device tree overlays is
unbinding the LED class device (pca9632@62) before unbinding the consumer
(backlight-addon):

  echo 11-0062 >/sys/bus/i2c/drivers/leds-pca963x/unbind
  echo ...backlight-dock >/sys/bus/platform/drivers/led-backlight/unbind

Fix by adding a devlink between the consuming led-backlight device and the
supplying LED device, as other drivers and subsystems do as well.

Fixes: ae232e45ac ("backlight: add led-backlight driver")
Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
Reviewed-by: Daniel Thompson (RISCstar) <danielt@kernel.org>
Reviewed-by: Herve Codina <herve.codina@bootlin.com>
Tested-by: Alexander Sverdlin <alexander.sverdlin@siemens.com>
Link: https://patch.msgid.link/20250519-led-backlight-add-devlink-to-supplier-class-device-v6-1-845224aeb2ce@bootlin.com
Signed-off-by: Lee Jones <lee@kernel.org>
This commit is contained in:
Luca Ceresoli 2025-05-19 22:19:11 +02:00 committed by Lee Jones
parent d95963e309
commit 9341d6698f
1 changed files with 13 additions and 0 deletions
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13
drivers/video/backlight/led_bl.c
View File

@ -210,6 +210,19 @@ static int led_bl_probe(struct platform_device *pdev)
return PTR_ERR(priv->bl_dev); return PTR_ERR(priv->bl_dev);
} }
for (i = 0; i < priv->nb_leds; i++) {
struct device_link *link;
link = device_link_add(&pdev->dev, priv->leds[i]->dev->parent,
DL_FLAG_AUTOREMOVE_CONSUMER);
if (!link) {
dev_err(&pdev->dev, "Failed to add devlink (consumer %s, supplier %s)\n",
dev_name(&pdev->dev), dev_name(priv->leds[i]->dev->parent));
backlight_device_unregister(priv->bl_dev);
return -EINVAL;
}
}
for (i = 0; i < priv->nb_leds; i++) { for (i = 0; i < priv->nb_leds; i++) {
mutex_lock(&priv->leds[i]->led_access); mutex_lock(&priv->leds[i]->led_access);
led_sysfs_disable(priv->leds[i]); led_sysfs_disable(priv->leds[i]);