drm/i915: Use the correct mdclk/cdclk ratio in MBUS updates

The current cdclk/mbus programming sequence is as follows:
1. intel_set_cdclk_pre_plane_update()
2. update_mbus_pre_enable()
3. intel_set_cdclk_post_plane_update()

when the actual mdclk/cdclk programming is postponed to
intel_set_cdclk_post_plane_update() we must keep using
the old mdclk/cdclk ratio during update_mbus_pre_enable().
This guarantees the programmed ratio matches the rest of
the hardware state (mdlk/cdclk/mbus joining).

v2: Extracted from the vblank synchronized mbus programming patch

Cc: Gustavo Sousa <gustavo.sousa@intel.com>
Reviewed-by: Uma Shankar <uma.shankar@intel.com> #v1
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240402155016.13733-12-ville.syrjala@linux.intel.com

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

@@ -2576,6 +2576,17 @@ static void intel_cdclk_pcode_post_notify(struct intel_atomic_state *state)
 			   update_cdclk, update_pipe_count);
 }
 
+bool intel_cdclk_is_decreasing_later(struct intel_atomic_state *state)
+{
+	const struct intel_cdclk_state *old_cdclk_state =
+		intel_atomic_get_old_cdclk_state(state);
+	const struct intel_cdclk_state *new_cdclk_state =
+		intel_atomic_get_new_cdclk_state(state);
+
+	return new_cdclk_state && !new_cdclk_state->disable_pipes &&
+		new_cdclk_state->actual.cdclk < old_cdclk_state->actual.cdclk;
+}
+
 /**
  * intel_set_cdclk_pre_plane_update - Push the CDCLK state to the hardware
  * @state: intel atomic state

drivers/gpu/drm/i915/display/intel_cdclk.h

@@ -69,6 +69,7 @@ bool intel_cdclk_clock_changed(const struct intel_cdclk_config *a,
 			       const struct intel_cdclk_config *b);
 u8 intel_mdclk_cdclk_ratio(struct drm_i915_private *i915,
 			   const struct intel_cdclk_config *cdclk_config);
+bool intel_cdclk_is_decreasing_later(struct intel_atomic_state *state);
 void intel_set_cdclk_pre_plane_update(struct intel_atomic_state *state);
 void intel_set_cdclk_post_plane_update(struct intel_atomic_state *state);
 void intel_cdclk_dump_config(struct drm_i915_private *i915,

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

@@ -3663,20 +3663,17 @@ static void intel_dbuf_mdclk_min_tracker_update(struct intel_atomic_state *state
 		intel_atomic_get_old_dbuf_state(state);
 	const struct intel_dbuf_state *new_dbuf_state =
 		intel_atomic_get_new_dbuf_state(state);
+	int mdclk_cdclk_ratio;
 
-	if (DISPLAY_VER(i915) >= 20 &&
-	    old_dbuf_state->mdclk_cdclk_ratio != new_dbuf_state->mdclk_cdclk_ratio) {
-		/*
-		 * For Xe2LPD and beyond, when there is a change in the ratio
-		 * between MDCLK and CDCLK, updates to related registers need to
-		 * happen at a specific point in the CDCLK change sequence. In
-		 * that case, we defer to the call to
-		 * intel_dbuf_mdclk_cdclk_ratio_update() to the CDCLK logic.
-		 */
-		return;
+	if (intel_cdclk_is_decreasing_later(state)) {
+		/* cdclk/mdclk will be changed later by intel_set_cdclk_post_plane_update() */
+		mdclk_cdclk_ratio = old_dbuf_state->mdclk_cdclk_ratio;
+	} else {
+		/* cdclk/mdclk already changed by intel_set_cdclk_pre_plane_update() */
+		mdclk_cdclk_ratio = new_dbuf_state->mdclk_cdclk_ratio;
 	}
 
-	intel_dbuf_mdclk_cdclk_ratio_update(i915, new_dbuf_state->mdclk_cdclk_ratio,
+	intel_dbuf_mdclk_cdclk_ratio_update(i915, mdclk_cdclk_ratio,
 					    new_dbuf_state->joined_mbus);
 }