linux-kernel - Re: [PATCH v2 00/17] Adding support for controlling the leds found on Intel NUC

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Date:   Thu, 20 May 2021 18:19:19 +0200
From:   Marek Behún <kabel@...nel.org>
To:     Mauro Carvalho Chehab <mchehab+huawei@...nel.org>
Cc:     Pavel Machek <pavel@....cz>, linuxarm@...wei.com,
        mauro.chehab@...wei.com, gregkh@...uxfoundation.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-leds@...r.kernel.org
Subject: Re: [PATCH v2 00/17] Adding support for controlling the leds found
 on Intel NUC

On Thu, 20 May 2021 01:07:20 +0200
Mauro Carvalho Chehab <mchehab+huawei@...nel.org> wrote:

> So, the first thing that the API needs is a way to tell what LED
> is monitoring the device's power state.

If a LED can monitor the device's power state in HW, register a LED
private trigger for this LED. If the LED is configured into this state
by default, you can set this trigger to be the default_trigger prior
registering the LED. The name of this private trigger can be
"hw:powerstate" or something like that (I wonder what others will
think about this name).

> Then, for each power state (S0, S3, S5), define if the LED will
> be ON all the times or not.
> 
> The "slowing breathing" is one of the possible blink patterns.
> The driver supports 4 other blink patterns
> 
> 	- Solid - the LED won't blink;
> 	- Breathing - it looks like a sinusoidal wave pattern;
> 	- Pulsing - it looks like a square wave pattern;
> 	- Strobing - it turns ON suddenly, and then it slowly turns OFF.
> 
> The speed of the blink is also adjustable, ranging from 0.1 Hz to 1 Hz,
> on 0.1 Hz steps.

Is the speed of breathing/strobing also adjustable? Or only when
pulsing?

When this "hw:powerstate" trigger is enabled for this LED,
only then another sysfs files should appear in this LED's sysfs
directory.

> ---
> 
> Let me explain this specific part of the API from my original proposal.
> 
> Those are the led names from the datasheets (NUC 8 and above),
> and my proposal for the sysfs class directory name:
> 
> =============	===============================
> LED name	sysfs
> =============	===============================
> Skull		``/sys/class/leds/nuc::skull``
> Skull eyes	``/sys/class/leds/nuc::eyes``
> Power		``/sys/class/leds/nuc::power``
> HDD		``/sys/class/leds/nuc::hdd``
> Front1		``/sys/class/leds/nuc::front1``
> Front2		``/sys/class/leds/nuc::front2``
> Front3		``/sys/class/leds/nuc::front3``
> =============	===============================
> 
> For each of the above, there's the need to identify what
> hardware function is monitored (if any).
> 
> My proposal were to add an "indicator" node (the name came from
> the Intel datasheets) that shows what led will monitor the power state.
> 
> Then, one blink_behavior and one blink_frequency per power state,
> e. g.:
> 
>     /sys/class/leds/nuc::front1
>     |-- indicator
>     |-- s0_blink_behavior
>     |-- s0_blink_frequency
>     |-- s3_blink_behavior
>     |-- s3_blink_frequency
>     |-- s5_blink_behavior
>     `-- s5_blink_frequency

I'd rather use one file for frequencies and one for intervals, and map
in to an array, but that is just my preference...

> 
> PS.: I don't care much about what names we'll use. Feel free to
> rename them, if you think the above is not clear or generic enough.
> 
> -
> 
> To make part of the API complete, there's also the need of a node
> to control the max brightness that the leds will achieve at the
> ON state, and another one to control the color on each state,
> as one could define, let's say, "white" when powered on, "blue"
> when suspended and "yellow" when hibernating. The colors at the
> NUC I have are RGB (but other models can use an enum for the
> supported colors).
> 
>     /sys/class/leds/nuc::front1
>     |-- s0_brightness
>     |-- s0_color		# only shown on colored leds
>     |-- s3_brightness
>     |-- s3_color		# only shown on colored leds
>     |-- s0_brightness
>     `-- s5_color		# only shown on colored leds

If the BIOS reports a LED being full RGB LED, you should register it
via multicolor framework. Regarding the enum with 8 colors: are these
colors red, yellow, green, cyan, blue, magenta? Because if so, then
this is RGB with each channel being binary :) So you can again use
multicolor framework.