drm/i915/display: WA for Re-initialize dispcnlunitt1 xosc clock

The dispcnlunit1_cp_xosc_clk should be de-asserted in display off
and only asserted in display on. As part of this workaround, Display
driver shall execute set-reset sequence at the end of the initialize
sequence to ensure clk does not remain active in display OFF.

--v2:
- Rebase.
--v3:
- Correct HSD number in commit message.
--v4:
- Reformat commit message.
- Use intel_de_rmw instead of intel_de_write
--v5:
- Build Fixes.

WA: 15013987218
Signed-off-by: Mitul Golani <mitulkumar.ajitkumar.golani@intel.com>
Reviewed-by: Nemesa Garg <nemesa.garg@intel.com>
Reviewed-by: Suraj Kandpal <suraj.kandpal@intel.com>
Signed-off-by: Suraj Kandpal <suraj.kandpal@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240708083247.2611258-1-mitulkumar.ajitkumar.golani@intel.com

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

@@ -1704,6 +1704,14 @@ static void icl_display_core_init(struct drm_i915_private *dev_priv,
 	/* Wa_14011503030:xelpd */
 	if (DISPLAY_VER(dev_priv) == 13)
 		intel_de_write(dev_priv, XELPD_DISPLAY_ERR_FATAL_MASK, ~0);
+
+	/* Wa_15013987218 */
+	if (DISPLAY_VER(dev_priv) == 20) {
+		intel_de_rmw(dev_priv, SOUTH_DSPCLK_GATE_D,
+			     0, PCH_GMBUSUNIT_CLOCK_GATE_DISABLE);
+		intel_de_rmw(dev_priv, SOUTH_DSPCLK_GATE_D,
+			     PCH_GMBUSUNIT_CLOCK_GATE_DISABLE, 0);
+	}
 }
 
 static void icl_display_core_uninit(struct drm_i915_private *dev_priv)