Re: [PATCH 2/4] drm/edid: parse HDMI 2.1 gaming (ALLM/VRR) capabilities from HF-VSDB

This is a core DRM patch and needs to be sent to dri-devel in
addition to amd-gfx.

On 2026-07-30 13:17, Fangzhi Zuo wrote:
> From: Tomasz Pakuła <[email protected]>
> 
> Parse the HDMI 2.1 gaming-related capabilities advertised in the HDMI
> Forum VSDB (HF-VSDB) and expose them through struct drm_hdmi_info so
> drivers can consume them.
> 
> Add struct drm_hdmi_vrr_cap describing the sink's VRR capabilities: Fast
> VActive (Quick Frame Transport), Negative M VRR, Cinema VRR, MDelta, and
> the VRRmin/VRRmax range, together with a "supported" flag derived from
> that range. Add the fapa_start_location and allm (Auto Low Latency Mode)
> flags to struct drm_hdmi_info.
> 
> drm_parse_hdmi_gaming_info() reads byte 8 of the HF-VSDB for the
> FAPA/ALLM/FVA/CNMVRR/CinemaVRR/MDelta flags and bytes 9-10 for
> VRRmin/VRRmax. Per HDMI 2.1, VRR is considered supported when VRRmin is
> within 1-48 and VRRmax is either 0 (maximum based on the video mode) or
>> = 100. It is invoked from drm_parse_hdmi_forum_scds(), and the parsed
> values are logged for debugging.
> 
> Signed-off-by: Fangzhi Zuo <[email protected]>
> Signed-off-by: Tomasz Pakuła <[email protected]>
> Tested-by: Bernhard Berger <[email protected]>

I didn't look at the HDMI spec myself, so can't vouch for the
correctness of the parser, but everything looks sane to me.

Reviewed-by: Harry Wentland <[email protected]>

Harry

> ---
>  drivers/gpu/drm/drm_edid.c  | 42 +++++++++++++++++++++++++++++++++
>  include/drm/drm_connector.h | 47 +++++++++++++++++++++++++++++++++++++
>  2 files changed, 89 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
> index a9d480981c8f..7f810b08a091 100644
> --- a/drivers/gpu/drm/drm_edid.c
> +++ b/drivers/gpu/drm/drm_edid.c
> @@ -6182,6 +6182,33 @@ static void drm_parse_ycbcr420_deep_color_info(struct drm_connector *connector,
>  	hdmi->y420_dc_modes = dc_mask;
>  }
>  
> +static void drm_parse_hdmi_gaming_info(struct drm_hdmi_info *hdmi, const u8 *db)
> +{
> +	struct drm_hdmi_vrr_cap *vrr = &hdmi->vrr_cap;
> +
> +	if (cea_db_payload_len(db) < 8)
> +		return;
> +
> +	hdmi->fapa_start_location = db[8] & DRM_EDID_FAPA_START_LOCATION;
> +	hdmi->allm = db[8] & DRM_EDID_ALLM;
> +	vrr->fva = db[8] & DRM_EDID_FVA;
> +	vrr->cnmvrr = db[8] & DRM_EDID_CNMVRR;
> +	vrr->cinema_vrr = db[8] & DRM_EDID_CINEMA_VRR;
> +	vrr->mdelta = db[8] & DRM_EDID_MDELTA;
> +
> +	if (cea_db_payload_len(db) < 9)
> +		return;
> +
> +	vrr->vrr_min = db[9] & DRM_EDID_VRR_MIN_MASK;
> +	vrr->supported = (vrr->vrr_min > 0 && vrr->vrr_min <= 48);
> +
> +	if (cea_db_payload_len(db) < 10)
> +		return;
> +
> +	vrr->vrr_max = (db[9] & DRM_EDID_VRR_MAX_UPPER_MASK) << 2 | db[10];
> +	vrr->supported &= (vrr->vrr_max == 0 || vrr->vrr_max >= 100);
> +}
> +
>  static void drm_parse_dsc_info(struct drm_hdmi_dsc_cap *hdmi_dsc,
>  			       const u8 *hf_scds)
>  {
> @@ -6308,6 +6335,8 @@ static void drm_parse_hdmi_forum_scds(struct drm_connector *connector,
>  
>  	drm_parse_ycbcr420_deep_color_info(connector, hf_scds);
>  
> +	drm_parse_hdmi_gaming_info(&connector->display_info.hdmi, hf_scds);
> +
>  	if (cea_db_payload_len(hf_scds) >= 11 && hf_scds[11]) {
>  		drm_parse_dsc_info(hdmi_dsc, hf_scds);
>  		dsc_support = true;
> @@ -6317,6 +6346,19 @@ static void drm_parse_hdmi_forum_scds(struct drm_connector *connector,
>  		    "[CONNECTOR:%d:%s] HF-VSDB: max TMDS clock: %d KHz, HDMI 2.1 support: %s, DSC 1.2 support: %s\n",
>  		    connector->base.id, connector->name,
>  		    max_tmds_clock, str_yes_no(max_frl_rate), str_yes_no(dsc_support));
> +	drm_dbg_kms(connector->dev,
> +		    "[CONNECTOR:%d:%s] FAPA in blanking: %s, ALLM support: %s, Fast Vactive support: %s\n",
> +		    connector->base.id, connector->name, str_yes_no(hdmi->fapa_start_location),
> +		    str_yes_no(hdmi->allm), str_yes_no(hdmi->vrr_cap.fva));
> +	drm_dbg_kms(connector->dev,
> +		    "[CONNECTOR:%d:%s] Negative M VRR support: %s, CinemaVRR support: %s, Mdelta: %d\n",
> +		    connector->base.id, connector->name, str_yes_no(hdmi->vrr_cap.cnmvrr),
> +		    str_yes_no(hdmi->vrr_cap.cinema_vrr), hdmi->vrr_cap.mdelta);
> +	drm_dbg_kms(connector->dev,
> +		    "[CONNECTOR:%d:%s] VRRmin: %u, VRRmax: %u, VRR supported: %s\n",
> +		    connector->base.id, connector->name, hdmi->vrr_cap.vrr_min,
> +		    hdmi->vrr_cap.vrr_max, str_yes_no(hdmi->vrr_cap.supported));
> +
>  }
>  
>  static void drm_parse_hdmi_deep_color_info(struct drm_connector *connector,
> diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h
> index 745cd917fe40..61ea6e866ea0 100644
> --- a/include/drm/drm_connector.h
> +++ b/include/drm/drm_connector.h
> @@ -254,6 +254,44 @@ struct drm_scdc {
>  	struct drm_scrambling scrambling;
>  };
>  
> +/**
> + * struct drm_hdmi_vrr_cap - Information about VRR capabilities of a HDMI sink
> + *
> + * Describes the VRR support provided by HDMI 2.1 sink. The information is
> + * fetched fom additional HFVSDB blocks defined for HDMI 2.1.
> + */
> +struct drm_hdmi_vrr_cap {
> +	/** @fva: flag for Fast VActive (Quick Frame Transport) support */
> +	bool fva;
> +
> +	/** @mcnmvrr: flag for Negative M VRR support */
> +	bool cnmvrr;
> +
> +	/** @mcinema_vrr: flag for Cinema VRR support */
> +	bool cinema_vrr;
> +
> +	/** @mdelta: flag for limited frame-to-frame compensation support */
> +	bool mdelta;
> +
> +	/**
> +	 * @vrr_min : minimum supported variable refresh rate in Hz.
> +	 * Valid values only inide 1 - 48 range
> +	 */
> +	u16 vrr_min;
> +
> +	/**
> +	 * @vrr_max : maximum supported variable refresh rate in Hz (optional).
> +	 * Valid values are either 0 (max based on video mode) or >= 100
> +	 */
> +	u16 vrr_max;
> +
> +	/**
> +	 * @supported: flag for vrr support based on checking for VRRmin and
> +	 * VRRmax values having correct values.
> +	 */
> +	bool supported;
> +};
> +
>  /**
>   * struct drm_hdmi_dsc_cap - DSC capabilities of HDMI sink
>   *
> @@ -330,6 +368,15 @@ struct drm_hdmi_info {
>  	/** @max_lanes: supported by sink */
>  	u8 max_lanes;
>  
> +	/** @fapa_start_location: flag for the FAPA in blanking support */
> +	bool fapa_start_location;
> +
> +	/** @allm: flag for Auto Low Latency Mode support by sink */
> +	bool allm;
> +
> +	/** @vrr_cap: VRR capabilities of the sink */
> +	struct drm_hdmi_vrr_cap vrr_cap;
> +
>  	/** @dsc_cap: DSC capabilities of the sink */
>  	struct drm_hdmi_dsc_cap dsc_cap;
>  };