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

[Jacek Anaszewski]

Hi,

On 2/16/19 11:03 PM, Hans de Goede wrote:
> Hi,
>
> On 2/16/19 10:54 PM, Jacek Anaszewski wrote:
> > 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.
>
> Right, but we can control the condition, so either we need to make
> the condition part of the pattern as in my recent proposal with:
>
> 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
>
> As hw_pattern ABI; or we need to add an extra sysfs file to
> set the condition.
>
> So do you prefer the driver to code the condition into the hw_pattern
> (see above); or do you prefer a separate sysfs attribute for the condition?

OK, so we'll need to add hardware_controlled file to the LED core.
It should be exposed only when supported by the hardware, so we will
need the flag in leds.h:

#define LED_DEV_CAP_HW_CONTROL BIT(24)

--
Best regards,
Jacek Anaszewski