drm/i915/adl_p: enable MSO on pipe B

On ADL-P, it's possible to enable the stream splitter on pipe B in
addition to pipe A.

Bspec: 50174
Cc: Uma Shankar <uma.shankar@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210526082903.26395-1-jani.nikula@intel.com

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

@@ -4729,9 +4729,12 @@ void intel_ddi_init(struct drm_i915_private *dev_priv, enum port port)
 
 		dig_port->hpd_pulse = intel_dp_hpd_pulse;
 
-		/* Splitter enable for eDP MSO is supported for pipe A only. */
-		if (dig_port->dp.mso_link_count)
+		/* Splitter enable for eDP MSO is limited to certain pipes. */
+		if (dig_port->dp.mso_link_count) {
 			encoder->pipe_mask = BIT(PIPE_A);
+			if (IS_ALDERLAKE_P(dev_priv))
+				encoder->pipe_mask |= BIT(PIPE_B);
+		}
 	}
 
 	/* In theory we don't need the encoder->type check, but leave it just in