6.6-stable review patch. If anyone has any objections, please let me know.
------------------
From: Luca Ceresoli luca.ceresoli@bootlin.com
[ Upstream commit 9341d6698f4cfdfc374fb6944158d111ebe16a9d ]
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: ae232e45acf9 ("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-clas... Signed-off-by: Lee Jones lee@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/video/backlight/led_bl.c | 13 +++++++++++++ 1 file changed, 13 insertions(+)
diff --git a/drivers/video/backlight/led_bl.c b/drivers/video/backlight/led_bl.c index 0e53e427a91dc..9089d17200ec7 100644 --- a/drivers/video/backlight/led_bl.c +++ b/drivers/video/backlight/led_bl.c @@ -209,6 +209,19 @@ static int led_bl_probe(struct platform_device *pdev) 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++) { mutex_lock(&priv->leds[i]->led_access); led_sysfs_disable(priv->leds[i]);