[Intel-gfx] [PATCH] drm/i915: FBC needs vblank before enable / disable.

[kiran.s.kumar at intel.com]

From: Kiran Kumar S <kiran.s.kumar at intel.corp-partner.google.com>

As per the display workaround #1200, FBC needs wait for vblank before
enabling and before disabling FBC.

In some cases, depending on whether FBC was compressing in that frame,
several control signals in the compression engine also will fail to
properly recognize the final segment of the frame as a result of the
missing last pixel indication. As a result of this, we're seeing
corrupted cache line/compression indicators after FBC re-enables
which causes underruns or corruption when they're used to decompress.

WA sequence as below:
1) Display enables plane 1A
2) Wait for 1 vblank
3) FBC gets enabled
4) Wait for 1 VBLANK
5) Turn off FBC

In GLK Chrome OS, if FBC is enabled by default, few top lines on the screen
got corrupted. With the above WA, issue was resolved.

Signed-off-by: Kiran Kumar S <kiran.s.kumar at intel.corp-partner.google.com>
---
 drivers/gpu/drm/i915/intel_display.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 8576a7f799f2..5118a36782eb 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -13207,8 +13207,11 @@ static void intel_update_crtc(struct drm_crtc *crtc,
 
 	if (pipe_config->update_pipe && !pipe_config->enable_fbc)
 		intel_fbc_disable(intel_crtc);
-	else if (new_plane_state)
+	else if (new_plane_state) {
+		/* Display WA #1200: GLK */
+		intel_wait_for_vblank(dev_priv, intel_crtc->pipe);
 		intel_fbc_enable(intel_crtc, pipe_config, new_plane_state);
+	}
 
 	intel_begin_crtc_commit(crtc, old_crtc_state);
 
@@ -13419,6 +13422,8 @@ static void intel_atomic_commit_tail(struct drm_atomic_state *state)
 
 			dev_priv->display.crtc_disable(old_intel_crtc_state, state);
 			intel_crtc->active = false;
+			/* Display WA #1200: GLK */
+			intel_wait_for_vblank(dev_priv, intel_crtc->pipe);
 			intel_fbc_disable(intel_crtc);
 			intel_disable_shared_dpll(old_intel_crtc_state);
 
-- 
2.7.4