RE: [PATCH v3 2/4] drm/edid: parse HDMI 2.1 gaming (ALLM/VRR) capabilities from HF-VSDB

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> -----Original Message-----
> From: Wentland, Harry <[email protected]>
> Sent: Tuesday, August 11, 2026 1:36 PM
> To: Zuo, Jerry <[email protected]>; [email protected];
> Maarten Lankhorst <[email protected]>; Maxime Ripard
> <[email protected]>; Thomas Zimmermann <[email protected]>;
> Deucher, Alexander <[email protected]>
> Cc: [email protected]; Tomasz Pakuła
> <[email protected]>; Bernhard Berger
> <[email protected]>
> Subject: Re: [PATCH v3 2/4] drm/edid: parse HDMI 2.1 gaming (ALLM/VRR)
> capabilities from HF-VSDB
>
> On 2026-08-10 20:39, 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: Tomasz Pakuła <[email protected]>
> > Signed-off-by: Fangzhi Zuo <[email protected]>
> > Tested-by: Bernhard Berger <[email protected]>
> > Reviewed-by: Harry Wentland <[email protected]>
>
> Maarten, Maxime, Thomas, I'd like to merge this into amd-staging-drm-next
> since other changes depend on it. Would you like me to push it to drm-misc-
> next as well or wait for amd-staging-drm-next pull to get it?
>
> Alex, any objections to taking this directly via asdn?

No objections from me.

Alex


>
> 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 ae26618a9a57..d508ec633c9b 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 cd06a3b914a0..9f8f109c2dd1
> 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;
> >  };