drm/i915/mtl: For DP2.0 10G and 20G rates use MPLLA

Use MPLLA for DP2.0 rates 10G and 20G, when ssc is enabled.

v2: Fix typo in commit message (Animesh)
Reviewed-by: Radhakrishna Sripada <radhakrishna.sripada@intel.com>
Reviewed-by: Arun R Murthy <arun.r.murthy@intel.com>
Signed-off-by: Mika Kahola <mika.kahola@intel.com>
Signed-off-by: Radhakrishna Sripada <radhakrishna.sripada@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230428095433.4109054-7-mika.kahola@intel.com

drivers/gpu/drm/i915/display/intel_cx0_phy.c

@@ -2349,8 +2349,11 @@ static void intel_program_port_clock_ctl(struct intel_encoder *encoder,
 		val |= XELPDP_DDI_CLOCK_SELECT(XELPDP_DDI_CLOCK_SELECT_MAXPCLK);
 
 	/* TODO: HDMI FRL */
-	/* TODO: DP2.0 10G and 20G rates enable MPLLA*/
-	val |= crtc_state->cx0pll_state.ssc_enabled ? XELPDP_SSC_ENABLE_PLLB : 0;
+	/* DP2.0 10G and 20G rates enable MPLLA*/
+	if (crtc_state->port_clock == 1000000 || crtc_state->port_clock == 2000000)
+		val |= crtc_state->cx0pll_state.ssc_enabled ? XELPDP_SSC_ENABLE_PLLA : 0;
+	else
+		val |= crtc_state->cx0pll_state.ssc_enabled ? XELPDP_SSC_ENABLE_PLLB : 0;
 
 	intel_de_rmw(i915, XELPDP_PORT_CLOCK_CTL(encoder->port),
 		     XELPDP_LANE1_PHY_CLOCK_SELECT | XELPDP_FORWARD_CLOCK_UNGATE |