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,
