| Message ID | 20250519-led-backlight-add-devlink-to-supplier-class-device-v6-1-845224aeb2ce@bootlin.com |
|---|---|
| State | Superseded |
| Headers | show |
| Series | [v6] backlight: led-backlight: add devlink to supplier LEDs | expand |
Hi Luca, On Mon, 19 May 2025 22:19:11 +0200 Luca Ceresoli <luca.ceresoli@bootlin.com> wrote: > 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.sverdlin@siemens.com> > Fixes: ae232e45acf9 ("backlight: add led-backlight driver") > Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com> Reviewed-by: Herve Codina <herve.codina@bootlin.com> Best regards, Hervé
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]);
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.sverdlin@siemens.com> Fixes: ae232e45acf9 ("backlight: add led-backlight driver") Signed-off-by: Luca Ceresoli <luca.ceresoli@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-v5-1-76d6fd4aeb2f@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-v5-1-76d6fd4aeb2f@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(+) --- base-commit: a5806cd506af5a7c19bcd596e4708b5c464bfd21 change-id: 20250519-led-backlight-add-devlink-to-supplier-class-device-6dec4e04445a Best regards,