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Date:   Sun, 17 Feb 2019 13:40:10 +0100
From:   Jacek Anaszewski <jacek.anaszewski@...il.com>
To:     Hans de Goede <hdegoede@...hat.com>, Pavel Machek <pavel@....cz>
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

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

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