KVASER_PCIEFD_KCAN_PWM_TOP_MASK
top = FIELD_GET(KVASER_PCIEFD_KCAN_PWM_TOP_MASK, pwm_ctrl);
pwm_ctrl |= FIELD_PREP(KVASER_PCIEFD_KCAN_PWM_TOP_MASK, top);
pwm_ctrl |= FIELD_PREP(KVASER_PCIEFD_KCAN_PWM_TOP_MASK, top);