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

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]>
---
 .../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,
-- 
2.53.0