Re: [PATCH v3 4/5] drm/bridge: nwl-dsi: Add error handling of nwl_dsi_mode_set()

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:

Pre-existing issues:
- [High] Unbalanced resource teardown and PM runtime underflow in mode_set error path.
--

--- Patch [4]: [PATCH v3 4/5] drm/bridge: nwl-dsi: Add error handling of nwl_dsi_mode_set() ---
commit 0db3c1cc2f73a9bc66aea2633f754029dd76b743
Author: Esben Haabendal <esben@geanix.com>

drm/bridge: nwl-dsi: Add error handling of nwl_dsi_mode_set()

This commit adds a return value check for nwl_dsi_mode_set() in
nwl_dsi_bridge_mode_set(), jumping to an error path on failure.

> diff --git a/drivers/gpu/drm/bridge/nwl-dsi.c b/drivers/gpu/drm/bridge/nwl-dsi.c
> index 3fd41212933c8..e90588299c5ea 100644
> --- a/drivers/gpu/drm/bridge/nwl-dsi.c
> +++ b/drivers/gpu/drm/bridge/nwl-dsi.c
> @@ -884,7 +884,9 @@ nwl_dsi_bridge_mode_set(struct drm_bridge *bridge,
>  	}
>  
>  	/* Step 2 from DSI reset-out instructions */
> -	nwl_dsi_mode_set(dsi);
> +	ret = nwl_dsi_mode_set(dsi);
> +	if (ret < 0)
> +		goto runtime_put;

[Severity: High]
This is a pre-existing issue, but does taking the runtime_put error path here
lead to unbalanced resource teardown and PM runtime underflows?

Because the drm_bridge_funcs.mode_set callback returns void, failures cannot be
propagated to the DRM core to abort the commit. If nwl_dsi_mode_set() fails and
jumps to runtime_put, it calls pm_runtime_put_sync() and returns early. 

However, the DRM core still considers the bridge pipeline state to be 'enabled',
and will unconditionally call nwl_dsi_bridge_atomic_disable() during the next
pipeline teardown.

When atomic_disable() runs, it unconditionally calls pm_runtime_put(), leading
to a reference count underflow:

drivers/gpu/drm/bridge/nwl-dsi.c:nwl_dsi_bridge_atomic_disable() {
	...
	pm_runtime_put(dsi->dev);
}

Furthermore, atomic_disable() unconditionally calls nwl_dsi_disable(), which
blindly attempts to tear down the PHY:

drivers/gpu/drm/bridge/nwl-dsi.c:nwl_dsi_bridge_atomic_disable() {
	...
	nwl_dsi_disable(dsi);
	...
}

Since nwl_dsi_mode_set() already cleans up its own PHY resources on internal
failure, this double-disable pushes the PHY framework's power_count and
init_count to -1. The next attempt to initialize the display will increment
these counters to 0, skipping the actual hardware ops->power_on() and
ops->init() calls, permanently leaving the display broken until the module is
reloaded.

While this broken error path already existed for clock initialization failures
in this function, wiring up nwl_dsi_mode_set's return value to it exposes the
PHY breakage on a new failure path.

>  
>  	/* Step 3 from DSI reset-out instructions */
>  	ret = reset_control_deassert(dsi->rst_esc);

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260810-nwl-dsi-fixes-v3-0-256da9d672e1@geanix.com?part=4