linux-kernel - Re: [RFC PATCH] leds: multicolor: Add sysfs interface definition

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Date:   Wed, 30 Jan 2019 21:20:09 +0100
From:   Jacek Anaszewski <jacek.anaszewski@...il.com>
To:     Dan Murphy <dmurphy@...com>, robh+dt@...nel.org, pavel@....cz
Cc:     linux-kernel@...r.kernel.org, linux-leds@...r.kernel.org
Subject: Re: [RFC PATCH] leds: multicolor: Add sysfs interface definition

Dan,

On 1/30/19 8:59 PM, Dan Murphy wrote:
> Jacek
> 
> On 1/30/19 1:37 PM, Jacek Anaszewski wrote:
>> Hi Dan,
>>
>> Thank you for the RFC.
>>
>> One vital thing is missing - documentation of brightness file must
>> be updated to define its semantics for LED multi color class.
>>
>> Either we need brightness-model file returning only "onoff" option
>> available, or, for time being, fix the max_brightness for LED multi
>> color class to 1 (which will map to max intensity level for each color).
>>
> 
> I can make max_brightness default to 1 if not set by the LED driver.
> 
> But the LP50xx has brightness controls so setting max_brightness from the driver should over ride
> the max of 1 in the upper level.

Yes, so the max_brightness should be updated basing on current
brightness-model. For LEDn_BRIGHTNESS of LP50xx we could have
"hw" or maybe even better just "lp50xx-linear" and "lp50xx-logarithmic"
- I just forgot about that capability of the device.

> For devices that do not support brightness as a separate control we can create a file called
> max_brightness_<color> that defines the max that a specific color can be set to.  If max_brightness
> is set to 1 then create max_brightness_<color>.  If max_brightness > 1 then do not create the files.

Right. We will need dedicated max_brightness for each color.
They should be placed also in the colors directory, next to the color
files.

> I don't think we have fully vetted the brightness-model yet so I prefer to omit
> it and possibly introduce that later.

We need to start from something. It will give better overview of the
whole idea.

Best regards,
Jacek Anaszewski

> Dan
> 
>> Best regards,
>> Jacek Anaszewski
>>
>> On 1/30/19 7:30 PM, Dan Murphy wrote:
>>> Add a documentation of LED Multicolor LED class specific
>>> sysfs attributes.
>>>
>>> Signed-off-by: Dan Murphy <dmurphy@...com>
>>> ---
>>>    .../ABI/testing/sysfs-class-led-multicolor    | 38 +++++++++++++++++++
>>>    1 file changed, 38 insertions(+)
>>>    create mode 100644 Documentation/ABI/testing/sysfs-class-led-multicolor
>>>
>>> diff --git a/Documentation/ABI/testing/sysfs-class-led-multicolor b/Documentation/ABI/testing/sysfs-class-led-multicolor
>>> new file mode 100644
>>> index 000000000000..19f8da9b150e
>>> --- /dev/null
>>> +++ b/Documentation/ABI/testing/sysfs-class-led-multicolor
>>> @@ -0,0 +1,38 @@
>>> +What:        /sys/class/leds/<led>/color/sync_enable
>>> +Date:        January 2019
>>> +KernelVersion:    5.0
>>> +Contact:    Dan Murphy <dmurphy@...com>
>>> +Description:    read/write
>>> +        Writing a 1 to this file will enable the sychronization of all
>>> +        the defined color LEDs within the LED node.  Writing a 0 to
>>> +        this file will disable syncing.
>>> +
>>> +What:        /sys/class/leds/<led>/color/sync
>>> +Date:        January 2019
>>> +KernelVersion:    5.0
>>> +Contact:    Dan Murphy <dmurphy@...com>
>>> +Description:    write only
>>> +        Writing a 1 to this file while sync_enable is set to 1 will
>>> +        synchronize all defined LEDs within the LED node.  All LEDs
>>> +        defined will be configured based on the brightness that has
>>> +        been requested.
>>> +
>>> +        If sync_enable is set to 0 then writing a 1 to sync has no
>>> +        affect on the LEDs.
>>> +
>>> +What:        /sys/class/leds/<led>/color/<led color>
>>> +Date:        January 2019
>>> +KernelVersion:    5.0
>>> +Contact:    Dan Murphy <dmurphy@...com>
>>> +Description:    read/write
>>> +        These files are dynamically created based on the colors defined
>>> +        by the registrar of the class.
>>> +        The led color(s) can be but not limited to red, green, blue,
>>> +        white, amber and violet.  If sync is enabled then writing the
>>> +        brightness value of the LED is deferred until a 1 is
>>> +        written to /sys/class/leds/<led>/color/sync.  If syncing is
>>> +        disabled then the LED brightness value will be written
>>> +        immediately to the LED driver.
>>> +
>>> +        The value of the color is from 0 to
>>> +        /sys/class/leds/<led>/max_brightness.
>>>
>>
> 
>