[Intel-gfx] [PATCH 16/16] drm/i915: Don't disable LP1+ watermarks for every frame when scaled

[ville.syrjala at linux.intel.com]

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

If we mark the LP1+ watermarks as disabled every time sprite scaling
is enabled, we end doing pointless work applying watermarks even though
nothing has changed. This is an artifact of the way
dev_priv->wm.lp_disabled affects the operation of
ilk_setup_pending_watermarks(). If the current pipe is included in
dev_priv->wm.lp_disabled, ilk_setup_pending_watermarks() will not check
if the watermarks actually changed since it will assume it will need to
disable LP1+ watermarks anyway.

A quick fix is to just check if sprite scaling was enabled for the
previous plane update, and if so, we know that LP1+ watermarks must
already be disabled. It might be better in long run to attempt to
change the way the LP1+ disable tracking integrates with the rest of
the watermark update mechanism. But this seems like a simple enough
solution for now.

Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
---
 drivers/gpu/drm/i915/intel_pm.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index ea1f990..0365ea6 100644
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -3180,7 +3180,8 @@ static int ilk_update_sprite_wm(struct intel_plane *plane,
 	 * 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))
+	if (IS_IVYBRIDGE(dev) && !params.spr.scaled &&
+	    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 &&
-- 
1.8.5.5