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

[Vidith Madhu <vmadhu@nvidia.com>]

On Mon, 21 Sep 2026, Nicolas Frattaroli wrote:

> From: Derek Foreman <derek.foreman@collabora.com>
> 
> Add VTEM EMP generation to enable variable refresh rate signalling over
> HDMI.
> 
> These infoframes are only generated if the sink supports VRR.
> 
> Signed-off-by: Derek Foreman <derek.foreman@collabora.com>
> Signed-off-by: Nicolas Frattaroli <nicolas.frattaroli@collabora.com>
> ---
>  drivers/gpu/drm/display/drm_hdmi_state_helper.c | 60 +++++++++++++++++++++++++
>  include/drm/drm_connector.h                     |  5 +++
>  2 files changed, 65 insertions(+)
> 
> diff --git a/drivers/gpu/drm/display/drm_hdmi_state_helper.c b/drivers/gpu/drm/display/drm_hdmi_state_helper.c
> index d55548399687..33d0c9491643 100644
> --- a/drivers/gpu/drm/display/drm_hdmi_state_helper.c
> +++ b/drivers/gpu/drm/display/drm_hdmi_state_helper.c
> @@ -853,6 +853,56 @@ static int hdmi_generate_hdmi_vendor_infoframe(const struct drm_connector *conne
>  	return 0;
>  }
>  
> +static int hdmi_generate_emp_infoframe_vtem(const struct drm_connector *connector,
> +					    struct drm_connector_state *conn_state)
> +{
> +	const struct drm_display_info *info = &connector->display_info;
> +	const struct drm_crtc_state *crtc_state =
> +		drm_atomic_get_crtc_state(conn_state->state, conn_state->crtc);
> +	struct drm_connector_hdmi_infoframe *infoframe =
> +		&conn_state->hdmi.infoframes.vtem;
> +	struct hdmi_emp_infoframe_vtem *vtem =
> +		&infoframe->data.vtem;
> +	const struct drm_crtc_vrr_state *vrr = &crtc_state->vrr_state;
> +	int vfront;
> +
> +	infoframe->set = false;
> +
> +	if (!connector->hdmi.funcs->vtem.write_infoframe)
> +		return 0;
> +
> +	if (!info->hdmi.vrr_capable)
> +		return 0;
> +
> +	hdmi_emp_infoframe_vtem_init(vtem);
> +	if (!crtc_state->vrr_enabled || vrr->vic) {
> +		vtem->base_refresh_rate = 0;
> +		vtem->base_vfront = 0;
It shouldn't hurt to always populate base_refresh_rate and base_vfront, 
might be cleaner to skip this check.
> +	} else {
> +		vtem->base_refresh_rate = drm_mode_vrefresh(&crtc_state->mode);
> +		vfront = crtc_state->adjusted_mode.crtc_vsync_start -
> +			 crtc_state->adjusted_mode.crtc_vdisplay;
> +		if (vfront > U8_MAX || vfront < 0)
> +			return -EINVAL;
> +
> +		vtem->base_vfront = vfront;
> +	}
> +	vtem->fva_factor_m1 = 0;
> +	infoframe->set = true;
> +
> +	if (!crtc_state->vrr_enabled) {
I don't think we should use the vrr_enabled CRTC property to determine 
VRR_EN in the VTEM EMP. Transitioning the VRR mode sink-side typically causes
blanking, and it was discussed in patch [03/25] that drivers should be 
free to handle vrr_enabled changes as a seamless switch since it only 
concerns source-side VRR state (this is how the NVIDIA driver handles it).
Maybe it would make sense to extend the qms_enabled connector property 
introduced in this patchset to an enum of {Off, Gaming, QMS}? This would allow
a standard path to control the VRR state on the sink, separately from
vrr_enabled. 
> +		vtem->m_const = false;
> +		vtem->game_vrr_en = false;
> +		return 0;
> +	}
> +
> +	vtem->game_vrr_en = true;
> +
> +	vtem->m_const = !vrr->dynamic;
> +
> +	return 0;
> +}
> +
>  static int
>  hdmi_generate_infoframes(const struct drm_connector *connector,
>  			 struct drm_connector_state *conn_state)
> @@ -884,6 +934,10 @@ hdmi_generate_infoframes(const struct drm_connector *connector,
>  	if (ret)
>  		return ret;
>  
> +	ret = hdmi_generate_emp_infoframe_vtem(connector, conn_state);
> +	if (ret)
> +		return ret;
> +
>  	return 0;
>  }
>  
> @@ -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;
> diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h
> index e561a444515f..6e431eb81705 100644
> --- a/include/drm/drm_connector.h
> +++ b/include/drm/drm_connector.h
> @@ -1180,6 +1180,11 @@ struct drm_connector_hdmi_state {
>  		 * matching our state.
>  		 */
>  		struct drm_connector_hdmi_infoframe hdmi;
> +
> +		/**
> +		 * @vtem: VTEM EMP infoframes structure matching our state.
> +		 */
> +		struct drm_connector_hdmi_infoframe vtem;
>  	} infoframes;
>  
>  	/**
> 
> -- 
> 2.55.0
> 
>