drm/amd/display: take a runtime PM reference only when a CRTC turns on

amdgpu_dm_commit_streams() takes a runtime PM reference for every
active CRTC that needs a modeset and has a new stream, but
amdgpu_dm_atomic_commit_tail() drops one only for each CRTC that goes
from active to inactive. A modeset of a CRTC that is already active (a
mode change, or anything else that needs a full modeset) therefore
leaks one reference. Once that has happened, the usage count no longer
returns to zero with every CRTC off, and the device cannot runtime
suspend again until reboot. The two also disagree the other way when a
CRTC turns on without a stream ("Failed to create new stream"): no
reference is taken, but one is dropped when it turns off.

Take the reference in the loop that counts the disabled CRTCs, on the
mirror condition: when the CRTC goes from inactive to active, which is
what the commit that added it intended ("every time we enable a
previously disabled CRTC"). Each active CRTC then holds exactly one
reference.

Tested on an RX 9070 XT (Navi 48) over OCuLink, with the change
backported to 7.2.9: an unplugged connector forced on, then mode A on a
CRTC, mode B on the same active CRTC, and the CRTC off, three rounds in
a row. The usage count rose by 3 with the stock module, by 0 with this
patch, and by 3 again after reloading the stock module.

Fixes: 97028037a38a ("drm/amdgpu: Grab/put runtime PM references in atomic_commit_tail()")
Closes: https://gitlab.freedesktop.org/drm/amd/-/issues/5951
Assisted-by: Claude:claude-opus-5-5
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Luigi Lauro <luigi.lauro@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit 59ef9a435499777b8e1c4e0eff52f813c64fb920)
Cc: stable@vger.kernel.org

1 files changed, 7 insertions, 4 deletions

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 5b634ae07c0d..caa5edcf1bc3 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
@@ -4709,8 +4709,6 @@ static void amdgpu_dm_commit_streams(struct drm_atomic_commit *state,
 			if (dm_old_crtc_state->stream)
 				remove_stream(adev, acrtc, dm_old_crtc_state->stream);
 
-			pm_runtime_get_noresume(dev->dev);
-
 			acrtc->enabled = true;
 			acrtc->hw_mode = new_crtc_state->mode;
 			crtc->hwmode = new_crtc_state->mode;
@@ -5294,8 +5292,13 @@ static void amdgpu_dm_atomic_commit_tail(struct drm_atomic_commit *state)
 #ifdef CONFIG_DEBUG_FS
 		enum amdgpu_dm_pipe_crc_source cur_crc_src;
 #endif
-		/* Count number of newly disabled CRTCs for dropping PM refs later. */
-		if (old_crtc_state->active && !new_crtc_state->active)
+		/*
+		 * One runtime PM reference per active CRTC: take it when the
+		 * CRTC turns on, count it when it turns off for dropping later.
+		 */
+		if (!old_crtc_state->active && new_crtc_state->active)
+			pm_runtime_get_noresume(dev->dev);
+		else if (old_crtc_state->active && !new_crtc_state->active)
 			crtc_disable_count++;
 
 		dm_new_crtc_state = to_dm_crtc_state(new_crtc_state);