[PATCH 2/2] drm/amd/display: Block immediate flips for non-fast updates

[Nicholas Kazlauskas]

[Why]
Underflow can occur in the case where we change buffer pitch, DCC state,
rotation or mirroring for a plane while also performing an immediate
flip. It can also generate a p-state warning stack trace on DCN1 which
is typically observed during the cursor handler pipe locking because of
how frequent cursor updates can occur.

[How]
Store the update type on each CRTC - every plane will have access to
the CRTC state if it's flipping. If the update type is not
UPDATE_TYPE_FAST then the immediate flip should be disallowed.

No changes to the target vblank sequencing need to be done, we just
need to ensure that the surface registers do a double buffered update.

Cc: David Francis <david.francis at amd.com>
Cc: Bhawanpreet Lakha <bhawanpreet.lakha at amd.com>
Cc: Leo Li <sunpeng.li at amd.com>
Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas at amd.com>
---
 .../gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c    | 16 +++++++++++++++-
 .../gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.h    |  1 +
 2 files changed, 16 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 ffb3c7247ac6..e941d0d3794b 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
@@ -5690,8 +5690,14 @@ static void amdgpu_dm_commit_planes(struct drm_atomic_state *state,
 		bundle->surface_updates[planes_count].plane_info =
 			&bundle->plane_infos[planes_count];
 
+		/*
+		 * Only allow immediate flips for fast updates that don't
+		 * change FB pitch, DCC state, rotation or mirroing.
+		 */
 		bundle->flip_addrs[planes_count].flip_immediate =
-				(crtc->state->pageflip_flags & DRM_MODE_PAGE_FLIP_ASYNC) != 0;
+			(crtc->state->pageflip_flags &
+			 DRM_MODE_PAGE_FLIP_ASYNC) != 0 &&
+			acrtc_state->update_type == UPDATE_TYPE_FAST;
 
 		timestamp_ns = ktime_get_ns();
 		bundle->flip_addrs[planes_count].flip_timestamp_in_us = div_u64(timestamp_ns, 1000);
@@ -7311,6 +7317,14 @@ static int amdgpu_dm_atomic_check(struct drm_device *dev,
 		state->async_update = !drm_atomic_helper_async_check(dev, state);
 	}
 
+	/* Store the overall update type for use later in atomic check. */
+	for_each_new_crtc_in_state (state, crtc, new_crtc_state, i) {
+		struct dm_crtc_state *dm_new_crtc_state =
+			to_dm_crtc_state(new_crtc_state);
+
+		dm_new_crtc_state->update_type = (int)overall_update_type;
+	}
+
 	/* Must be success */
 	WARN_ON(ret);
 	return ret;
diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.h b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.h
index da48a857949f..cbd6608f58e6 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.h
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.h
@@ -307,6 +307,7 @@ struct dm_crtc_state {
 	bool cm_has_degamma;
 	bool cm_is_degamma_srgb;
 
+	int update_type;
 	int active_planes;
 	bool interrupts_enabled;
 
-- 
2.17.1