Re: [PATCH RFC 06/25] drm/connector: hdmi: Add VTEM EMP generation

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] drm: VTEM infoframe not cleared when switching to non-VRR sink
--

commit 5a4e1a050c5d27ea6b13e207c2d853adeb273ef9
Author: Derek Foreman <derek.foreman@collabora.com>

drm/connector: hdmi: Add VTEM EMP generation

This commit adds VTEM EMP generation to enable variable refresh rate
signalling over HDMI. The infoframes are generated if the sink supports VRR.

> diff --git a/drivers/gpu/drm/display/drm_hdmi_state_helper.c b/drivers/gpu/drm/display/drm_hdmi_state_helper.c
> index d555483996874..33d0c94916430 100644
> --- a/drivers/gpu/drm/display/drm_hdmi_state_helper.c
> +++ b/drivers/gpu/drm/display/drm_hdmi_state_helper.c
[ ... ]
> @@ -1494,6 +1548,12 @@ int drm_atomic_helper_connector_hdmi_update_infoframes(struct drm_connector *con
>  			goto out;
>  	}
>  
> +	if (info->hdmi.vrr_capable)
> +		ret = write_or_clear_infoframe(connector,
> +					&funcs->vtem, "VTEM",
> +					&old_conn_state->hdmi.infoframes.vtem,
> +					&new_conn_state->hdmi.infoframes.vtem);
> +
>  out:
>  	mutex_unlock(&connector->hdmi.infoframes.lock);
>  	return ret;

[Severity: Medium]
What happens if a VRR-capable sink is disconnected and replaced by a non-VRR
sink?

If info->hdmi.vrr_capable becomes false, the guard in
drm_atomic_helper_connector_hdmi_update_infoframes() evaluates to false and
skips write_or_clear_infoframe() for VTEM.

This means the hardware is never commanded to clear the VTEM infoframe via
funcs->clear_infoframe(), leading to stale VTEM packets being continuously
transmitted to a sink that does not support them.

Could this cause a hardware state mismatch and potential compliance issues?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260921-vrr-limiter-uapi-v1-0-2fcd7d011646@collabora.com?part=6