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

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Message-ID: <af5bec7b-0da1-ee19-cdf4-0240f56221ad@redhat.com>
Date:   Sat, 16 Feb 2019 20:01:49 +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 6:02 PM, Jacek Anaszewski wrote:
> Hi Hans,
> 
> On 2/16/19 12:14 AM, Hans de Goede wrote:
>> Hi,
>>
>> On 2/15/19 11:31 PM, Jacek Anaszewski wrote:
>>> On 2/15/19 11:26 PM, Hans de Goede wrote:
>>
>> <snip>
>>
>>>> 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 ?

Regards,

Hans