[PATCH 6.18.y] drm/amd/display: set allow_freesync before validating a new stream

[Sasha Levin <sashal@kernel.org>]

From: Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com>

[ Upstream commit ab18dd3061eb2d92e60c8bbf9a435c25962e449f ]

After resume from S3, DC enables SubVP on a single FreeSync display at
a high refresh rate, although dcn32_allow_subvp_high_refresh_rate() is
meant to keep SubVP off that configuration ("For single display cases,
freesync must be disabled").  On an RX 7900 XTX driving a FreeSync TV
at 3840x2160@120, amdgpu_dm_capabilities reports sub-viewport disabled
after boot and enabled after "rtcwake -m mem", and the memory clock
starts switching.  It stays that way until a later commit re-validates
the state; a CRTC gamma change (toggling Night Light) turns SubVP off
again.

The policy reads dc_stream_state::allow_freesync while the new state
is validated, but amdgpu_dm sets that field only in
amdgpu_dm_update_freesync_state_on_stream(), on the first flip after
the commit.  A stream created by a modeset is therefore validated as
if FreeSync were off.  On resume, dm_destroy_cached_state() drops the
streams and forces a modeset, so the resumed state is validated
without FreeSync.

Set allow_freesync in amdgpu_dm_get_freesync_config_for_crtc(), which
atomic check calls for every active CRTC and which already writes
ignore_msa_timing_param to the stream.  It uses vrr_supported, the
condition the flip-time value is derived from.  With this change the
same TV keeps SubVP disabled across "rtcwake -m mem".

On this machine SubVP is also what exposes the single-frame scanout
corruption reported in the thread linked below, so the FreeSync
setting stopped working as a workaround after every suspend.

Fixes: 87f0c16e0eeb ("drm/amd/display: Enable SubVP for high refresh rate displays")
Link: https://lore.kernel.org/all/20260829010525.29935-1-mikhail.v.gavrilov@gmail.com/
Link: https://gitlab.freedesktop.org/drm/amd/-/work_items/5714#note_3736349
Tested-by: Josh Kasten <jkasten@gmail.com>
Signed-off-by: Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com>
Reviewed-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit 29793918b0eb63b6810b248a906f87dd79b70be5)
Cc: stable@vger.kernel.org
[ sashal: Applied the unchanged addition to get_freesync_config_for_crtc(), since the FreeSync helper extraction and renaming are absent. ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 8 ++++++++
 1 file changed, 8 insertions(+)

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 a77b55ff9321f..40ac1a33326fa 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
@@ -11350,6 +11350,14 @@ static void get_freesync_config_for_crtc(
 					vrefresh >= aconnector->min_vfreq &&
 					vrefresh <= aconnector->max_vfreq;
 
+	/*
+	 * DC reads allow_freesync while validating the new state, for example
+	 * to keep SubVP off a single FreeSync display, but it is otherwise set
+	 * only on the first flip after the commit.  Set it here, so that a
+	 * stream created by this commit is not validated without it.
+	 */
+	new_crtc_state->stream->allow_freesync = new_crtc_state->vrr_supported;
+
 	if (new_crtc_state->vrr_supported) {
 		new_crtc_state->stream->ignore_msa_timing_param = true;
 		fs_vid_mode = new_crtc_state->freesync_config.state == VRR_STATE_ACTIVE_FIXED;
-- 
2.53.0