DP_EDP_PWMGEN_BIT_COUNT
ret = drm_dp_dpcd_write_byte(aux, DP_EDP_PWMGEN_BIT_COUNT, bl->pwmgen_bit_count);
ret = drm_dp_dpcd_read_byte(aux, DP_EDP_PWMGEN_BIT_COUNT, &pn);
ret = drm_dp_dpcd_write_byte(aux, DP_EDP_PWMGEN_BIT_COUNT, pn);