drm/i915/mtl: Fix SSC selection for MPLLA

Driver does not clear the default SSC for MPLLA. This causes link training
failure when trying to use 10G and 20G rates. Fix the behaviour and enable
ssc only when we really want.

Fixes: 237e7be ("drm/i915/mtl: For DP2.0 10G and 20G rates use MPLLA")
Cc: Mika Kahola <[email protected]>
Cc: Clint Taylor <[email protected]>
Cc: Khaled Almahallawy <[email protected]>
Cc: Arun R Murthy <[email protected]>
Signed-off-by: Radhakrishna Sripada <[email protected]>
Tested-by: Khaled Almahallawy <[email protected]>
Reviewed-by: Mika Kahola <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]
(cherry picked from commit 7e8d87e)
Signed-off-by: Tvrtko Ursulin <[email protected]>

Author: Radhakrishna Sripada

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

@@ -2435,7 +2435,8 @@ static void intel_program_port_clock_ctl(struct intel_encoder *encoder,
 
 	intel_de_rmw(i915, XELPDP_PORT_CLOCK_CTL(encoder->port),
 		     XELPDP_LANE1_PHY_CLOCK_SELECT | XELPDP_FORWARD_CLOCK_UNGATE |
-		     XELPDP_DDI_CLOCK_SELECT_MASK | XELPDP_SSC_ENABLE_PLLB, val);
+		     XELPDP_DDI_CLOCK_SELECT_MASK | XELPDP_SSC_ENABLE_PLLA |
+		     XELPDP_SSC_ENABLE_PLLB, val);
 }
 
 static u32 intel_cx0_get_powerdown_update(u8 lane_mask)