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

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Date:   Sat, 16 Feb 2019 20:37:27 +0100
From:   Pavel Machek <pavel@....cz>
To:     Hans de Goede <hdegoede@...hat.com>
Cc:     Jacek Anaszewski <jacek.anaszewski@...il.com>,
        Yauhen Kharuzhy <jekhor@...il.com>,
        linux-kernel@...r.kernel.org, linux-leds@...r.kernel.org
Subject: Re: [PATCH v2 1/2] leds: Add Intel Cherry Trail Whiskey Cove PMIC
 LEDs

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.

Best regards,
								Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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