[Intel-gfx] [PATCH v4 2/5] drm/i915: Force recalculate min_cdclk if planes config changed

[Stanislav Lisovskiy]

In Gen11+ whenever we might exceed DBuf bandwidth we might need to
recalculate CDCLK which DBuf bandwidth is scaled with.
Total Dbuf bw used might change based on particular plane needs.

In intel_atomic_check_planes we try to filter out the cases when
we definitely don't need to recalculate required bandwidth/CDCLK.
In current code we compare amount of planes and skip recalculating
if those are equal.
This seems being too relaxed requirement and might be even wrong
because plane combination might become different despite amount
of planes is same - that requires recalculating min cdclk and
consumed bandwidth.

v2: - Changed commit message to properly reflect the need why,
      we might want to change from hamming weight comparison
      to actual plane combination checking.

Signed-off-by: Stanislav Lisovskiy <stanislav.lisovskiy at intel.com>
---
 drivers/gpu/drm/i915/display/intel_display.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c
index c77088e1d033..307636b23ac9 100644
--- a/drivers/gpu/drm/i915/display/intel_display.c
+++ b/drivers/gpu/drm/i915/display/intel_display.c
@@ -14540,7 +14540,7 @@ static bool active_planes_affects_min_cdclk(struct drm_i915_private *dev_priv)
 	/* See {hsw,vlv,ivb}_plane_ratio() */
 	return IS_BROADWELL(dev_priv) || IS_HASWELL(dev_priv) ||
 		IS_CHERRYVIEW(dev_priv) || IS_VALLEYVIEW(dev_priv) ||
-		IS_IVYBRIDGE(dev_priv);
+		IS_IVYBRIDGE(dev_priv) || (INTEL_GEN(dev_priv) >= 11);
 }
 
 static int intel_atomic_check_planes(struct intel_atomic_state *state,
@@ -14586,7 +14586,13 @@ static int intel_atomic_check_planes(struct intel_atomic_state *state,
 		old_active_planes = old_crtc_state->active_planes & ~BIT(PLANE_CURSOR);
 		new_active_planes = new_crtc_state->active_planes & ~BIT(PLANE_CURSOR);
 
-		if (hweight8(old_active_planes) == hweight8(new_active_planes))
+		/*
+		 * Not only the number of planes, but if the plane configuration had
+		 * changed might already mean we need to recompute min CDCLK,
+		 * because different planes might consume different amount of Dbuf bandwidth
+		 * according to formula: Bw per plane = Pixel rate * bpp * pipe/plane scale factor
+		 */
+		if (old_active_planes == new_active_planes)
 			continue;
 
 		ret = intel_crtc_add_planes_to_state(state, crtc, new_active_planes);
-- 
2.24.1.485.gad05a3d8e5