[PATCH 3/4] drm/i915: Use vblank worker to unpin old legacy cursor fb safely

[Chaitanya Kumar Borah]

From: Ville Syrjälä <ville.syrjala at linux.intel.com>

The cursor hardware only does sync updates, and thus the hardware
will be scanning out from the old fb until the next start of vblank.
So in order to make the legacy cursor fastpath actually safe we
should not unpin the old fb until we're sure the hardware has
ceased accessing it. The simplest approach is to just use a vblank
work here to do the delayed unpin.

Not 100% sure it's a good idea to put this onto the same high
priority vblank worker as eg. our timing critical gamma updates.
But let's keep it simple for now, and it we later discover that
this is causing problems we can think about adding a lower
priority worker for such things.

In case we are shutting down the crtc after vblank workers are
scheduled and before vblank arrives, drm_handle_vblank_works()
never gets called. This will lead to cancellation of the vblank
worker during drm_crtc_vblank_off(), therefore, wait one vblank
if there are pending vblank workers.

This patch is slightly reworked by Maarten.

Cc: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
Signed-off-by: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
Signed-off-by: Chaitanya Kumar Borah <chaitanya.kumar.borah at intel.com>
---
 drivers/gpu/drm/i915/display/intel_cursor.c   | 26 +++++++++++++++++--
 drivers/gpu/drm/i915/display/intel_display.c  |  6 +++++
 .../drm/i915/display/intel_display_types.h    |  3 +++
 3 files changed, 33 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_cursor.c b/drivers/gpu/drm/i915/display/intel_cursor.c
index 2118b87ccb10..c9963f5d546e 100644
--- a/drivers/gpu/drm/i915/display/intel_cursor.c
+++ b/drivers/gpu/drm/i915/display/intel_cursor.c
@@ -674,6 +674,17 @@ static bool intel_cursor_format_mod_supported(struct drm_plane *_plane,
 	return format == DRM_FORMAT_ARGB8888;
 }
 
+static void intel_cursor_unpin_work(struct kthread_work *base)
+{
+	struct drm_vblank_work *work = to_drm_vblank_work(base);
+	struct intel_plane_state *plane_state =
+		container_of(work, typeof(*plane_state), unpin_work);
+	struct intel_plane *plane = to_intel_plane(plane_state->uapi.plane);
+
+	intel_plane_unpin_fb(plane_state);
+	intel_plane_destroy_state(&plane->base, &plane_state->uapi);
+}
+
 static int
 intel_legacy_cursor_update(struct drm_plane *_plane,
 			   struct drm_crtc *_crtc,
@@ -817,14 +828,25 @@ intel_legacy_cursor_update(struct drm_plane *_plane,
 
 	intel_psr_unlock(crtc_state);
 
-	intel_plane_unpin_fb(old_plane_state);
+	if (old_plane_state->ggtt_vma != new_plane_state->ggtt_vma) {
+		drm_vblank_work_init(&old_plane_state->unpin_work, &crtc->base,
+				     intel_cursor_unpin_work);
+
+		drm_vblank_work_schedule(&old_plane_state->unpin_work,
+					 drm_crtc_accurate_vblank_count(&crtc->base) + 1,
+					 false);
+
+		old_plane_state = NULL;
+	} else {
+		intel_plane_unpin_fb(old_plane_state);
+	}
 
 out_free:
 	if (new_crtc_state)
 		intel_crtc_destroy_state(&crtc->base, &new_crtc_state->uapi);
 	if (ret)
 		intel_plane_destroy_state(&plane->base, &new_plane_state->uapi);
-	else
+	else if (old_plane_state)
 		intel_plane_destroy_state(&plane->base, &old_plane_state->uapi);
 	return ret;
 
diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c
index ef986b508431..bd428e04236f 100644
--- a/drivers/gpu/drm/i915/display/intel_display.c
+++ b/drivers/gpu/drm/i915/display/intel_display.c
@@ -65,6 +65,7 @@
 #include "intel_crt.h"
 #include "intel_crtc.h"
 #include "intel_crtc_state_dump.h"
+#include "intel_cursor.h"
 #include "intel_ddi.h"
 #include "intel_de.h"
 #include "intel_display_driver.h"
@@ -6923,6 +6924,11 @@ static void intel_commit_modeset_disables(struct intel_atomic_state *state)
 			continue;
 
 		intel_crtc_disable_planes(state, crtc);
+
+		if(drm_vblank_has_pending_work(&crtc->base)) {
+			intel_crtc_wait_for_next_vblank(crtc);
+			drm_vblank_work_flush_all(&crtc->base);
+		}
 	}
 
 	/* Only disable port sync and MST slaves */
diff --git a/drivers/gpu/drm/i915/display/intel_display_types.h b/drivers/gpu/drm/i915/display/intel_display_types.h
index 00eba3fbcdc6..e2ccec8d36ff 100644
--- a/drivers/gpu/drm/i915/display/intel_display_types.h
+++ b/drivers/gpu/drm/i915/display/intel_display_types.h
@@ -730,6 +730,9 @@ struct intel_plane_state {
 	struct intel_fb_view view;
 	u32 phys_dma_addr; /* for cursor_needs_physical */
 
+	/* for legacy cursor fb unpin */
+	struct drm_vblank_work unpin_work;
+
 	/* Plane pxp decryption state */
 	bool decrypt;
 
-- 
2.25.1