SPRD_PWM_MOD_MAX
tmp = (prescale + 1) * NSEC_PER_SEC * SPRD_PWM_MOD_MAX;
duty = duty_ns * SPRD_PWM_MOD_MAX / period_ns;
prescale = DIV_ROUND_CLOSEST_ULL(tmp, SPRD_PWM_MOD_MAX) - 1;
sprd_pwm_write(spc, pwm->hwpwm, SPRD_PWM_MOD, SPRD_PWM_MOD_MAX);