| Message ID | 20240917-hotplug-drm-bridge-v4-6-bc4dfee61be6@bootlin.com |
|---|---|
| State | New |
| Headers | show |
| Series | Add support for GE SUNH hot-pluggable connector | expand |
On Tue, Sep 17, 2024 at 10:53:10AM +0200, Luca Ceresoli wrote: > 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 This looks like the object became invalid whilst we were holding a reference to it. Is that reasonable? Put another way, is using devlink here fixing a bug or merely hiding one? Daniel.
Hello Daniel, On Thu, 19 Sep 2024 14:43:23 +0200 Daniel Thompson <daniel.thompson@linaro.org> wrote: > On Tue, Sep 17, 2024 at 10:53:10AM +0200, Luca Ceresoli wrote: > > 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 > > This looks like the object became invalid whilst we were holding a reference > to it. Is that reasonable? Put another way, is using devlink here fixing a > bug or merely hiding one? Thanks for your comment. Hervé and I just had a look at the code and there actually might be a bug here, which we will be investigating (probably next week). Still I think the devlink needs to be added to describe the relationship between the supplier (LED) and consumer (backlight). Luca
diff --git a/drivers/video/backlight/led_bl.c b/drivers/video/backlight/led_bl.c index c7aefcd6e4e3..bfbd80728036 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]);
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> --- This patch first appeared in v4. --- drivers/video/backlight/led_bl.c | 13 +++++++++++++ 1 file changed, 13 insertions(+)