static int pwm_backlight_update_status(struct backlight_device *bl)

  {

   struct pwm_bl_data *pb = bl_get_data(bl);

      int brightness = bl->props.brightness;

      int duty_cycle;

     if (bl->props.power != FB_BLANK_UNBLANK ||

         bl->props.fb_blank != FB_BLANK_UNBLANK ||

         bl->props.state & BL_CORE_FBBLANK)

         brightness = ;

     if (pb->notify)

         brightness = pb->notify(pb->dev, brightness);

//此处修改区间值

     if (brightness > ) {

        if(brightness<)

             brightness=;

         duty_cycle = compute_duty_cycle(pb, brightness);

         pwm_config(pb->pwm, duty_cycle, pb->period);

         pwm_backlight_power_on(pb, brightness);

     } else

         pwm_backlight_power_off(pb);

     if (pb->notify_after)

         pb->notify_after(pb->dev, brightness);

     return ;

 }