Re: [PATCH v2 1/2] led: led-class: Read max-brightness from devicetree

[Astrid Rost]

Hello Jacek,

I am having problems with the PWM controller LP5024.

https://www.ti.com/product/LP5024

There is no such a calculation in the data-sheet like:
max_brightness = max_current / constant.

I also assume it is depending on the type of LEDs and circuit, which are 
connected.

It supports two current modes: 25,5 mA and and 35 mA, both is to high 
for the LEDs I have.

For max_brightness seems to be everything inside the kernel, but reading 
the value from devicetree. I first thought I could add it in the lp50xx
driver, but Andy and Rob thought that I better put it into the general 
parts. And of course drivers having led-max-microamp should better use it.

Please, let me know if you have a better suggestion.

Astrid





On 7/1/23 13:09, Jacek Anaszewski wrote:
> Hi Astrid,
>
> On 6/30/23 11:22, Astrid Rost wrote:
> > Add max-brightness in order to reduce the current on the connected LEDs.
> > Normally, the maximum brightness is determined by the hardware, and this
> > property is not required. This property is used to set a software limit.
> > It could happen that an LED is made so bright that it gets damaged or
> > causes damage due to restrictions in a specific system, such as mounting
> > conditions. Note that led-max-microamp should be preferably used, if it
> > is supported by the controller.
> >
> > Signed-off-by: Astrid Rost <astrid.rost@xxxxxxxx>
> > ---
> >   drivers/leds/led-class.c | 4 ++++
> >   1 file changed, 4 insertions(+)
> >
> > diff --git a/drivers/leds/led-class.c b/drivers/leds/led-class.c
> > index 9255bc11f99d..ce652abf9336 100644
> > --- a/drivers/leds/led-class.c
> > +++ b/drivers/leds/led-class.c
> > @@ -457,6 +457,10 @@ int led_classdev_register_ext(struct device *parent,
> >               if (fwnode_property_present(init_data->fwnode,
> >                               "retain-state-shutdown"))
> >                   led_cdev->flags |= LED_RETAIN_AT_SHUTDOWN;
> > +
> > +            fwnode_property_read_u32(init_data->fwnode,
> > +                "max-brightness",
> > +                &led_cdev->max_brightness);
> >           }
> >       } else {
> >           proposed_name = led_cdev->name;
>
> We have led-max-microamp for that and every LED class driver is supposed
> to calculate its max brightness level basing on it.