DP_VOLTAGE_MASK
intel_dp->DP &= ~(DP_VOLTAGE_MASK | DP_PRE_EMPHASIS_MASK);
#define DP_VOLTAGE_0_4 REG_FIELD_PREP(DP_VOLTAGE_MASK, 0)
#define DP_VOLTAGE_0_6 REG_FIELD_PREP(DP_VOLTAGE_MASK, 1)
#define DP_VOLTAGE_0_8 REG_FIELD_PREP(DP_VOLTAGE_MASK, 2)
#define DP_VOLTAGE_1_2 REG_FIELD_PREP(DP_VOLTAGE_MASK, 3)