drm/i915: Disable live M/N updates when using bigjoiner

All joined pipes share the same transcoder/timing generator.
Currently we just do the commits per-pipe, which doesn't really
work if we need to change the timings at the same time. For
now just disable live M/N updates when bigjoiner is needed.

Cc: stable@vger.kernel.org
Tested-by: Vidya Srinivas <vidya.srinivas@intel.com>
Reviewed-by: Arun R Murthy <arun.r.murthy@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240404213441.17637-5-ville.syrjala@linux.intel.comSigned-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

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

@@ -2752,7 +2752,11 @@ intel_dp_drrs_compute_config(struct intel_connector *connector,
 		intel_panel_downclock_mode(connector, &pipe_config->hw.adjusted_mode);
 	int pixel_clock;
 
-	if (has_seamless_m_n(connector))
+	/*
+	 * FIXME all joined pipes share the same transcoder.
+	 * Need to account for that when updating M/N live.
+	 */
+	if (has_seamless_m_n(connector) && !pipe_config->bigjoiner_pipes)
 		pipe_config->update_m_n = true;
 
 	if (!can_enable_drrs(connector, pipe_config, downclock_mode)) {