[PATCH 14/31][SRU][OEM-5.6] drm/i915: Don't check for wm changes until we've compute the wms fully

[You-Sheng Yang]

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

BugLink: https://bugs.launchpad.net/bugs/1891451

Currently we're comparing the watermarks between the old and new states
before we've fully computed the new watermarks. In particular
skl_build_pipe_wm() will not account for the amount of ddb space we'll
have. That information is only available during skl_compute_ddb()
which will proceed to zero out any watermark level exceeding the
ddb allocation. If we're short on ddb space this will end up
adding the plane to the state due erronously determining that the
watermarks have changed. Fix the problem by deferring
skl_wm_add_affected_planes() until we have the final watermarks
computed.

Noticed this when trying enable transition watermarks on glk.
We now computed the trans_wm as 28, but we only had 14 blocks
of ddb, and thus skl_compute_ddb() ended up disabling the cursor
trans_wm every time. Thus we ended up adding the cursor to every
commit that didn't actually affect the cursor at all.

Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200228203552.30273-2-ville.syrjala@linux.intel.com
Reviewed-by: José Roberto de Souza <jose.souza at intel.com>
(cherry picked from commit 23baedd217effd594bdf4620c1fea4d27febe090)
Signed-off-by: You-Sheng Yang <vicamo.yang at canonical.com>
---
 drivers/gpu/drm/i915/intel_pm.c | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index d25726666177..e5460b470f1f 100644
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -5769,16 +5769,24 @@ skl_compute_wm(struct intel_atomic_state *state)
 		ret = skl_build_pipe_wm(new_crtc_state);
 		if (ret)
 			return ret;
-
-		ret = skl_wm_add_affected_planes(state, crtc);
-		if (ret)
-			return ret;
 	}
 
 	ret = skl_compute_ddb(state);
 	if (ret)
 		return ret;
 
+	/*
+	 * skl_compute_ddb() will have adjusted the final watermarks
+	 * based on how much ddb is available. Now we can actually
+	 * check if the final watermarks changed.
+	 */
+	for_each_oldnew_intel_crtc_in_state(state, crtc, old_crtc_state,
+					    new_crtc_state, i) {
+		ret = skl_wm_add_affected_planes(state, crtc);
+		if (ret)
+			return ret;
+	}
+
 	skl_print_wm_changes(state);
 
 	return 0;
-- 
2.27.0