[PATCH 15/16] drm/i915: Add a workaround for sprite only <-> primary only switching

[ville.syrjala@linux.intel.com]

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

ILK and IVB don't like switching between sprite only and primary only
configurations when LP1+ watermarks have been enabled in the recent
past. Like WaCxSRDisabledForSpriteScaling we can avoid the flash
by disabling LP1+ watermarks for one frame before the critical plane
reconfiguration.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
---
 drivers/gpu/drm/i915/intel_pm.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index 66af79d..ea1f990 100644
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -3175,9 +3175,18 @@ static int ilk_update_sprite_wm(struct intel_plane *plane,
 	 * when scaling is disabled.
 	 *
 	 * WaCxSRDisabledForSpriteScaling:ivb
+	 *
+	 * We also seem to need something similar when switching between
+	 * primary only and sprite only configurations. Otherwise the screen
+	 * flashes black. No underrun reported though.
 	 */
 	if (IS_IVYBRIDGE(dev) && config->spr.scaled && ilk_disable_lp_wm(crtc))
 		intel_wait_for_vblank(dev, plane->pipe);
+	else if (config->pri.enabled != config->spr.enabled &&
+		 config->pri.enabled != params.pri.enabled &&
+		 config->spr.enabled != params.spr.enabled &&
+		 ilk_disable_lp_wm(crtc))
+		intel_wait_for_vblank(dev, plane->pipe);
 
 	params.pri = config->pri;
 	params.spr = config->spr;
-- 
1.8.5.5

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