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.
Tested-by: Alexander Sverdlin <alexander.sverd...@siemens.com>
Fixes: ae232e45acf9 ("backlight: add led-backlight driver")
Signed-off-by: Luca Ceresoli <luca.ceres...@bootlin.com>
---
Changes in v6:
- EDITME: describe what is new in this series revision.
- EDITME: use bulletpoints and terse descriptions.
- Link to v5:
https://lore.kernel.org/r/20250519-led-backlight-add-devlink-to-supplier-class-device-v5-1-76d6fd4ae...@bootlin.com
---
Changes in v6:
- fix incorrect array index
- further improve commit message
- Link to v5:
https://lore.kernel.org/r/20250519-led-backlight-add-devlink-to-supplier-class-device-v5-1-76d6fd4ae...@bootlin.com
Changes in v5:
- separated this patch as a standalone patch
- improved commit message, adding feedback from Alexander
- no code changes
This patch first appeared in the v4 of a longer series, even though the
issue is orthogonal:
https://lore.kernel.org/all/20240917-hotplug-drm-bridge-v4-6-bc4dfee61...@bootlin.com/
---
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
d2db157b2c290adc3a159023e9e2394fc877388c..0ed585eb27903df43651c5365f479f7865cc8a95
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]);
---
base-commit: a5806cd506af5a7c19bcd596e4708b5c464bfd21
change-id:
20250519-led-backlight-add-devlink-to-supplier-class-device-6dec4e04445a
Best regards,
--
Luca Ceresoli <luca.ceres...@bootlin.com>
