drivers/video/backlight/led_bl.c | 13 +++++++++++++ 1 file changed, 13 insertions(+)
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. 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>;
};
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.sverdlin@siemens.com>
Fixes: ae232e45acf9 ("backlight: add led-backlight driver")
Signed-off-by: Luca Ceresoli <luca.ceresoli@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-bc4dfee61be6@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..8fe645b5b75447d009e1045dcf0c62d3bbc5425e 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[0]->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[0]->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.ceresoli@bootlin.com>Hi Luca,
On Mon, 19 May 2025 17:16:39 +0200
Luca Ceresoli <luca.ceresoli@bootlin.com> wrote:
...
> diff --git a/drivers/video/backlight/led_bl.c b/drivers/video/backlight/led_bl.c
> index d2db157b2c290adc3a159023e9e2394fc877388c..8fe645b5b75447d009e1045dcf0c62d3bbc5425e 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[0]->dev->parent,
It should be priv->leds[i]->dev->parent instead of leds[0], shouldn't it?
> + 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[0]->dev->parent));
ditto
> + 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]);
>
Best regards,
Hervé
Hi Hervé,
On Mon, 19 May 2025 17:47:29 +0200
Herve Codina <herve.codina@bootlin.com> wrote:
> Hi Luca,
>
> On Mon, 19 May 2025 17:16:39 +0200
> Luca Ceresoli <luca.ceresoli@bootlin.com> wrote:
>
> ...
>
> > diff --git a/drivers/video/backlight/led_bl.c b/drivers/video/backlight/led_bl.c
> > index d2db157b2c290adc3a159023e9e2394fc877388c..8fe645b5b75447d009e1045dcf0c62d3bbc5425e 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[0]->dev->parent,
>
> It should be priv->leds[i]->dev->parent instead of leds[0], shouldn't it?
Ah, well spotted, thanks!
My led-backlight device only uses one LED, so I hadn't noticed during
testing.
v6 on its way.
Luca
--
Luca Ceresoli, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com
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