Re: [PATCH] drm/bridge: microchip-lvds: Fix runtime PM leak in mchp_lvds_enable()

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] drm/bridge: runtime PM usage counter underflow on atomic_enable error
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commit f6da183dff281321349d56635d572cdbbecf6393
Author: Wentao Liang <vulab@iscas.ac.cn>

drm/bridge: microchip-lvds: Fix runtime PM leak in mchp_lvds_enable()

This patch attempts to fix a runtime PM usage counter leak in
mchp_lvds_atomic_enable() by dropping the reference when
pm_runtime_get_sync() fails.

> diff --git a/drivers/gpu/drm/bridge/microchip-lvds.c b/drivers/gpu/drm/bridge/microchip-lvds.c
> index dd4ffc9f4df3f..f30ebeea4a4da 100644
> --- a/drivers/gpu/drm/bridge/microchip-lvds.c
> +++ b/drivers/gpu/drm/bridge/microchip-lvds.c
> @@ -144,6 +144,7 @@ static void mchp_lvds_atomic_enable(struct drm_bridge *bridge,
>  	ret = pm_runtime_get_sync(lvds->dev);
>  	if (ret < 0) {
>  		dev_err(lvds->dev, "failed to get pm runtime: %d\n", ret);
> +		pm_runtime_put_noidle(lvds->dev);

[Severity: Medium]
Will this lead to a runtime PM usage counter underflow when the bridge is
disabled?

The DRM bridge API's atomic_enable callback returns void, so the DRM core
cannot be notified of a failure. If pm_runtime_get_sync() fails, the DRM core
still considers the bridge enabled and will unconditionally call
mchp_lvds_atomic_disable() during the next modeset or pipeline teardown.

Since this patch locally drops the PM reference here on the error path, the
unconditional pm_runtime_put() in mchp_lvds_atomic_disable() will decrement
the usage count a second time, causing an underflow. Before this patch, the
reference left by the failing get_sync() balanced the unconditional put in
the disable path.

>  		return;
>  	}

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Sashiko AI review · https://sashiko.dev/#/patchset/20260916101922.2018259-1-vulab@iscas.ac.cn?part=1