Re: [PATCH v2 1/2] leds: Add Intel Cherry Trail Whiskey Cove PMIC LEDs

[Jacek Anaszewski]

On 2/16/19 8:37 PM, Pavel Machek wrote:
> Hi!
>
> > > > > > I think that should work fine, which means that we can use the timer and
> > > > > > pattern trigger support for the blinking and breathing modes.
> > > > > >
> > > > > > That still leaves the switching between user and hw-control modes,
> > > > > > as discussed the hw-controlled mode could be modelled as a new "hardware"
> > > > > > trigger, but then we cannot choose between on/blink/breathing when
> > > > > > in hw-controlled mode. As Pavel mentioned, that would require some
> > > > > > sort of composed trigger, where we have both the hardware and
> > > > > > timer triggers active for example.
> > > > > >
> > > > > > I think it might be easier to just allow turning on/off the hardware
> > > > > > control mode through a special "hardware_control" sysfs attribute and
> > > > > > then use the existing timer and pattern triggers for blinking / breathing.
> > > > >
> > > > > Pattern trigger exposes pattern file by default and hw_pattern if
> > > > > pattern_set/get ops are provided. Writing them enables software and
> > > > > hardware pattern respectively.
> > > >
> > > > This is not about software vs hardware pattern.
> > > >
> > > > There are 2 *orthogonal*, separate problems/challenges with this LED controller:
> > > >
> > > > 1) It has hardware blinking and breathing, as discussed this can be
> > > > controlled through the timer and pattern triggers, so this problem
> > > > is solved.
> > > >
> > > > 2) It has 2 operating modes:
> > > >
> > > > a) Automatic/hardware controlled, in this mode the LED is turned
> > > > off or on (where on can be continues on, blinking or breathing)
> > > > by the hardware itself, when in this mode we / userspace is not
> > > > in control of the LED
> > > >
> > > > b) Manual/user controlled mode, in this mode we / userspace can
> > > > control of the LED.
> > > >
> > > > Currently there is no API in the ledclass to switch a LED from
> > > > automatic controlled to user controlled and back, This is what
> > > > the proposed hardware trigger was for, to switch to automatic
> > > > mode. A problem with this is that we still want to be able
> > > > to chose between continues on, blinking or breathing (when on),
> > > > configure the max brightness, etc.
> > >
> > > Yes, we do have the API to switch a LED from automatic (hardware
> > > accelerated) control to software control and back. This is pattern
> > > trigger, which exposes two files for setting pattern: pattern
> > > and hw_pattern. Writing pattern file switches the device to software
> > > control mode and writing hw_pattern switches it to the hardware control,
> > > with the possibility of defining device specific ABI syntax to enable
> > > particular pattern (blinking, breathing or event permanently on
> > > in case of this device).
> >
> > OK, I see. So we would use the hw_pattern for this and the driver
> > would implement the pattern_set led_classdev callback.
> >
> > The pattern_set callback would then expect 6 brightness/time tuples
> > with the following meaning for the time part of each tupple
> >
> > tupple0: charging blinking_on_time
> > tupple1: charging blinking_off_time
> > tupple2: charging breathing_time
> > tupple3: manual blinking_on_time
> > tupple4: manual blinking_off_time
> > tupple5: manual breathing_time
> >
> > Where only the times in tupple 0-2; or the times in 3-5 can be
> > non-zero. Having non zero times for both some charging and some
> > manual values is not allowed.
> >
> > If a breathing time is set, none of the other times may be non
> > 0. If blinkig_on and blinking_off are used then breathing_time
> > must be 0.
> >
> > When configured to blink then blinking_off must be either 0
> > (continuously on); or it must be the same as blinking_on.
> >
> >
> > I believe this will work, does this sound ok to you ?
>
> I don't pretend to fully understand it, _but_ hw_pattern should really
> describe the pattern LED should do, not whether it reacts to charging
> or not.

This is hardware specific and is supposed to have dedicated ABI
documentation. There's no reason to introduce new mechanisms when
existing ones fit. It will still describe a pattern but activated
on some condition.

--
Best regards,
Jacek Anaszewski