drm/i915: Check plane configuration properly

Checking with hweight8 if plane configuration had
changed seems to be wrong as different plane configs
can result in a same hamming weight.
So lets check the bitmask itself.

v2: Fixed "from" field which got corrupted for some weird reason

Reviewed-by: Manasi Navare <manasi.d.navare@intel.com>
Signed-off-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
Signed-off-by: Manasi Navare <manasi.d.navare@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200520145827.15887-1-stanislav.lisovskiy@intel.com

Author: StanFox1984

drivers/gpu/drm/i915/display/intel_display.c

@@ -14688,7 +14688,13 @@ 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);