[Intel-gfx] [PATCH] drm/i915: do not reset PLANE_SURF on plane disable on older gens

[Andrzej Hajda <andrzej.hajda@intel.com>]

In case of ICL and older generations disabling plane and/or disabling
async update is always performed on vblank, but if async update is enabled
PLANE_SURF register is updated asynchronously. Writing 0 to PLANE_SURF
when plane is still enabled can cause DMAR/PIPE errors.
On the other side PLANE_SURF is used to arm plane registers - we need to
write to it to trigger update on VBLANK, writting current value should
be safe - the buffer address is valid till vblank.

Signed-off-by: Andrzej Hajda <andrzej.hajda@intel.com>
---
 drivers/gpu/drm/i915/display/skl_universal_plane.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/skl_universal_plane.c b/drivers/gpu/drm/i915/display/skl_universal_plane.c
index bcfde81e4d0866..bc9ed60a2d349e 100644
--- a/drivers/gpu/drm/i915/display/skl_universal_plane.c
+++ b/drivers/gpu/drm/i915/display/skl_universal_plane.c
@@ -615,11 +615,13 @@ skl_plane_disable_arm(struct intel_plane *plane,
 	struct drm_i915_private *dev_priv = to_i915(plane->base.dev);
 	enum plane_id plane_id = plane->id;
 	enum pipe pipe = plane->pipe;
+	u32 plane_surf;
 
 	skl_write_plane_wm(plane, crtc_state);
 
 	intel_de_write_fw(dev_priv, PLANE_CTL(pipe, plane_id), 0);
-	intel_de_write_fw(dev_priv, PLANE_SURF(pipe, plane_id), 0);
+	plane_surf = intel_de_read_fw(dev_priv, PLANE_SURF(pipe, plane_id));
+	intel_de_write_fw(dev_priv, PLANE_SURF(pipe, plane_id), plane_surf);
 }
 
 static void
@@ -629,6 +631,7 @@ icl_plane_disable_arm(struct intel_plane *plane,
 	struct drm_i915_private *dev_priv = to_i915(plane->base.dev);
 	enum plane_id plane_id = plane->id;
 	enum pipe pipe = plane->pipe;
+	u32 plane_surf;
 
 	if (icl_is_hdr_plane(dev_priv, plane_id))
 		intel_de_write_fw(dev_priv, PLANE_CUS_CTL(pipe, plane_id), 0);
@@ -637,7 +640,8 @@ icl_plane_disable_arm(struct intel_plane *plane,
 
 	intel_psr2_disable_plane_sel_fetch(plane, crtc_state);
 	intel_de_write_fw(dev_priv, PLANE_CTL(pipe, plane_id), 0);
-	intel_de_write_fw(dev_priv, PLANE_SURF(pipe, plane_id), 0);
+	plane_surf = intel_de_read_fw(dev_priv, PLANE_SURF(pipe, plane_id));
+	intel_de_write_fw(dev_priv, PLANE_SURF(pipe, plane_id), plane_surf);
 }
 
 static bool
-- 
2.25.1