Re: [PATCH v4 4/4] drm/amd/display: Enable HDMI ALLM for Gaming-VRR

On 2026-08-14 12:43, Fangzhi Zuo wrote:
> why:
> HDMI 2.1 Auto Low-Latency Mode (ALLM) lets a Source request the Sink's
> low-latency mode through the HF-VSIF. HDMI 2.1 Section 7.6.6 requires
> that when Gaming-VRR is enabled (VRR_EN=1) and the Sink advertises ALLM
> in the SCDS, the Source shall transmit the HF-VSIF and set ALLM_Mode=1.
> amdgpu never set ALLM_Mode, so this requirement was not met.
> 
> how:
> - In update_freesync_state_on_stream(), set ALLM_Mode=1 in the HF-VSIF
>   when Gaming-VRR is active (vrr state ACTIVE_VARIABLE/ACTIVE_FIXED,
>   i.e. VRR_EN=1) and the sink advertises ALLM, per HDMI 2.1 Section
>   7.6.6, and push the updated HF-VSIF (vsp_infopacket) as a stream
>   update.
> 
> ALLM is driven only by the mandatory Gaming-VRR case.
> 
> Signed-off-by: Fangzhi Zuo <[email protected]>

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

Harry

> ---
>  .../gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c |  5 +++-
>  .../display/amdgpu_dm/amdgpu_dm_freesync.c    | 29 +++++++++++++++++++
>  2 files changed, 33 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> index 567bf04979ee..ff0db0cb9880 100644
> --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> @@ -4029,9 +4029,12 @@ static void amdgpu_dm_commit_planes(struct drm_atomic_commit *state,
>  		}
>  
>  		if (acrtc_state->stream) {
> -			if (acrtc_state->freesync_vrr_info_changed)
> +			if (acrtc_state->freesync_vrr_info_changed) {
>  				bundle->stream_update.vrr_infopacket =
>  					&acrtc_state->stream->vrr_infopacket;
> +				bundle->stream_update.vsp_infopacket =
> +					&acrtc_state->stream->vsp_infopacket;
> +			}
>  		}
>  	}
>  
> diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_freesync.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_freesync.c
> index 382c339b67b1..63d10cb7f5ed 100644
> --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_freesync.c
> +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_freesync.c
> @@ -252,6 +252,35 @@ void amdgpu_dm_update_freesync_state_on_stream(
>  	new_stream->vrr_infopacket = vrr_infopacket;
>  	new_stream->allow_freesync = mod_freesync_get_freesync_enabled(&vrr_params);
>  
> +	/*
> +	 * HDMI ALLM: when Gaming-VRR is active (VRR_EN=1) and the sink
> +	 * advertises ALLM in the SCDS, the Source shall transmit the HF-VSIF
> +	 * with ALLM_Mode=1 (HDMI 2.1 Section 7.6.6).
> +	 */
> +	if (new_stream->signal == SIGNAL_TYPE_HDMI_TYPE_A ||
> +	    new_stream->signal == SIGNAL_TYPE_HDMI_FRL) {
> +		struct dc_info_packet vsp_infopacket = {0};
> +		bool sink_allm = aconn && aconn->base.display_info.hdmi.allm;
> +		bool allm = sink_allm &&
> +			(vrr_params.state == VRR_STATE_ACTIVE_VARIABLE ||
> +			 vrr_params.state == VRR_STATE_ACTIVE_FIXED);
> +		bool allm_changed;
> +
> +		mod_build_hf_vsif_infopacket(new_stream, &vsp_infopacket, allm, allm);
> +
> +		allm_changed = memcmp(&new_stream->vsp_infopacket, &vsp_infopacket,
> +				      sizeof(vsp_infopacket)) != 0;
> +		new_crtc_state->freesync_vrr_info_changed |= allm_changed;
> +		new_stream->vsp_infopacket = vsp_infopacket;
> +
> +		if (allm_changed)
> +			drm_dbg_driver(adev_to_drm(adev),
> +				       "ALLM: flip on crtc=%u: sink_allm=%d vrr_state=%d -> ALLM_Mode=%d\n",
> +				    new_crtc_state->base.crtc->base.id,
> +				    sink_allm,
> +				    vrr_params.state, allm);
> +	}
> +
>  	if (new_crtc_state->freesync_vrr_info_changed)
>  		drm_dbg_kms(adev_to_drm(adev), "VRR packet update: crtc=%u enabled=%d state=%d",
>  			      new_crtc_state->base.crtc->base.id,