Message-ID: <fc178a78-8e12-1892-3fde-21333e65667c@redhat.com>
Date:   Sat, 16 Feb 2019 23:03:08 +0100
From:   Hans de Goede <hdegoede@...hat.com>
To:     Jacek Anaszewski <jacek.anaszewski@...il.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 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?

Regards,

Hans

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