Date:   Sat, 16 Feb 2019 22:54:57 +0100
From:   Jacek Anaszewski <jacek.anaszewski@...il.com>
To:     Pavel Machek <pavel@....cz>, Hans de Goede <hdegoede@...hat.com>
Cc:     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

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

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