Hi Daniel,
...
> > +static int mp3309c_bl_update_status(struct backlight_device *bl) {
> > + struct mp3309c_chip *chip = bl_get_data(bl);
> > + int brightness = backlight_get_brightness(bl);
> > + struct pwm_state pwmstate;
> > + unsigned int analog_val, bits_val;
> > + int i, ret;
> > +
> > + if (chip->pdata->dimming_mode == DIMMING_PWM) {
> > + /*
> > + * PWM dimming mode
> > + */
> > + pwm_get_state(chip->pwmd, &pwmstate);
> > + pwm_set_relative_duty_cycle(&pwmstate, brightness,
> > + chip->pdata->max_brightness);
> > + pwmstate.enabled = true;
> > + ret = pwm_apply_state(chip->pwmd, &pwmstate);
> > + if (ret)
> > + return ret;
> > +
> > + switch (chip->pdata->status) {
> > + case FIRST_POWER_ON:
> > + case BACKLIGHT_OFF:
> > + /*
> > + * After 20ms of low pwm signal level, the chip turns
> > + off automatically. In this case, before enabling the
> > + chip again, we must wait about 10ms for pwm signal
> to
> > + stabilize.
> > + */
> > + if (brightness > 0) {
> > + msleep(10);
> > + mp3309c_enable_device(chip);
> > + chip->pdata->status = BACKLIGHT_ON;
> > + } else {
> > + chip->pdata->status = BACKLIGHT_OFF;
> > + }
> > + break;
> > + case BACKLIGHT_ON:
> > + if (brightness == 0)
> > + chip->pdata->status = BACKLIGHT_OFF;
> > + break;
> > + }
> > + } else {
> > + /*
> > + * Analog dimming (by I2C command) dimming mode
> > + *
> > + * The first time, before setting brightness, we must enable the
> > + * device
> > + */
> > + if (chip->pdata->status == FIRST_POWER_ON)
> > + mp3309c_enable_device(chip);
> > +
> > + /*
> > + * Dimming mode I2C command
> > + *
> > + * The 5 bits of the dimming analog value D4..D0 is allocated
> > + * in the I2C register #0, in the following way:
> > + *
> > + * +--+--+--+--+--+--+--+--+
> > + * |EN|D0|D1|D2|D3|D4|XX|XX|
> > + * +--+--+--+--+--+--+--+--+
> > + */
> > + analog_val = DIV_ROUND_UP(ANALOG_MAX_VAL *
> brightness,
> > + chip->pdata->max_brightness);
>
> Sorry to only notice after sharing a Reviewed-by:[1] but...
>
> Scaling brightness here isn't right. When running in I2C dimming mode then
> max_brightness *must* be 31 or lower, meaning the value in brightness can
> be applied directly to the hardware without scaling.
ok, right; max brightness is 31, fixed
>
> Quoting the DT binding docs about how max-brightness should be
> interpretted:
>
> Normally the maximum brightness is determined by the hardware and this
> property is not required. This property is used to put a software
> limit on the brightness apart from what the driver says, as it could
> happen that a LED can be made so bright that it gets damaged or causes
> damage due to restrictions in a specific system, such as mounting
> conditions.
>
ok
>
> Daniel.
>
>
> [1] I remember checking if this code could overflow the field but I was
> so distracted by that I ended up missing the obvious!
Thanks and best regards,
Flavio
