drm/i915/xelpd: Fix unclaimed accesses while loading PIPEDMC-C/D

At the moment on DG2 at least loading the DMC firmware's PIPEDMC C and D
programs leads to sporadic unclaimed register accesses while programming
the initial state as described by the firmware's "MMIO init" table. This
will also lead to later unclaimed accesses for unrelated transcoder/pipe
registers backed by the pipe C and D display power wells.

Disabling the PIPEDMC clock gating during initialization - similarly to
Wa_16015201720 fixed this problem in my tests. While pipe A an B
requires the clock gating to be disabled all the time pipe C and D
requires this only while accessing the PIPEDMC registers.

Bspec: 49193
References: https://gitlab.freedesktop.org/drm/intel/-/issues/6526
References: https://gitlab.freedesktop.org/drm/intel/-/issues/6308Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Arun R Murthy <arun.r.murthy@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220808103054.3586074-1-imre.deak@intel.com

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

@@ -1615,14 +1615,6 @@ static void icl_display_core_init(struct drm_i915_private *dev_priv,
 		intel_de_rmw(dev_priv, SOUTH_DSPCLK_GATE_D, 0,
 			     PCH_DPMGUNIT_CLOCK_GATE_DISABLE);
 
-	/* Wa_16015201720:adl-p,dg2 */
-	if (DISPLAY_VER(dev_priv) == 13) {
-		intel_de_rmw(dev_priv, CLKGATE_DIS_PSL_EXT(PIPE_A),
-			     0, PIPEDMC_GATING_DIS);
-		intel_de_rmw(dev_priv, CLKGATE_DIS_PSL_EXT(PIPE_B),
-			     0, PIPEDMC_GATING_DIS);
-	}
-
 	/* 1. Enable PCH reset handshake. */
 	intel_pch_reset_handshake(dev_priv, !HAS_PCH_NOP(dev_priv));
 

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

@@ -383,6 +383,30 @@ static void disable_all_event_handlers(struct drm_i915_private *i915)
 	}
 }
 
+static void pipedmc_clock_gating_wa(struct drm_i915_private *i915, bool enable)
+{
+	enum pipe pipe;
+
+	if (DISPLAY_VER(i915) != 13)
+		return;
+
+	/*
+	 * Wa_16015201720:adl-p,dg2
+	 * The WA requires clock gating to be disabled all the time
+	 * for pipe A and B.
+	 * For pipe C and D clock gating needs to be disabled only
+	 * during initializing the firmware.
+	 */
+	if (enable)
+		for (pipe = PIPE_A; pipe <= PIPE_D; pipe++)
+			intel_de_rmw(i915, CLKGATE_DIS_PSL_EXT(pipe),
+				     0, PIPEDMC_GATING_DIS);
+	else
+		for (pipe = PIPE_C; pipe <= PIPE_D; pipe++)
+			intel_de_rmw(i915, CLKGATE_DIS_PSL_EXT(pipe),
+				     PIPEDMC_GATING_DIS, 0);
+}
+
 /**
  * intel_dmc_load_program() - write the firmware from memory to register.
  * @dev_priv: i915 drm device.
@@ -399,6 +423,8 @@ void intel_dmc_load_program(struct drm_i915_private *dev_priv)
 	if (!intel_dmc_has_payload(dev_priv))
 		return;
 
+	pipedmc_clock_gating_wa(dev_priv, true);
+
 	disable_all_event_handlers(dev_priv);
 
 	assert_rpm_wakelock_held(&dev_priv->runtime_pm);
@@ -432,6 +458,8 @@ void intel_dmc_load_program(struct drm_i915_private *dev_priv)
 	 * here.
 	 */
 	disable_all_flip_queue_events(dev_priv);
+
+	pipedmc_clock_gating_wa(dev_priv, false);
 }
 
 /**
@@ -446,7 +474,9 @@ void intel_dmc_disable_program(struct drm_i915_private *i915)
 	if (!intel_dmc_has_payload(i915))
 		return;
 
+	pipedmc_clock_gating_wa(i915, true);
 	disable_all_event_handlers(i915);
+	pipedmc_clock_gating_wa(i915, false);
 }
 
 void assert_dmc_loaded(struct drm_i915_private *i915)