linux-kernel - Re: [RFC PATCH 3/5] documention: leds: Add multicolor class documentation

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Date:   Tue, 2 Apr 2019 06:53:30 -0500
From:   Dan Murphy <dmurphy@...com>
To:     Pavel Machek <pavel@....cz>
CC:     <robh+dt@...nel.org>, <jacek.anaszewski@...il.com>,
        <marek.behun@....cz>, <linux-kernel@...r.kernel.org>,
        <linux-leds@...r.kernel.org>
Subject: Re: [RFC PATCH 3/5] documention: leds: Add multicolor class
 documentation

Pavel

Thanks for the comments

On 4/1/19 4:27 PM, Pavel Machek wrote:
> Hi!
> 
>> +Under the "colors" directory there are two files created "sync" and
>> +"sync_enable". The sync_enable file controls whether the LED brightness
>> +value is set real time or if the LED brightness value setting is deferred until
>> +the "sync" file is written.  If sync_enable is set then writing to each LED
>> +"brightness" file will store the brightness value.  Once the "sync" file is
>> +written then each LED color defined in the node will write the brightness of
>> +the LED in the device driver.
>> +
>> +If "sync_enable" is not set then writing the brightness value of the LED to the
>> +device driver is done immediately.  Writing the "sync" file has no
>> affect.
> 
> I believe better solutions exists for this problem.
> 

I agree there are other solutions.  Better not so sure.
We keep kicking a solution down the road we have been talking about adding something to the kernel
for almost 5 months now, but no one can decide what to do.

How do we move a solution forward?
Should we just forget the whole idea and keep developing against the current framework?

> One was discussed before -- have single file which contains
> coefficients for r/g/b channels.
> 

That has been presented as well and the concept was not well received either.

> Or at least... you should not really need separate sync and
> sync_enable files. One should do.
> 

The idea here was to be able to set the LED brightness immediately on a single LED
with a single brightness write or setup the color brightness on all the LEDs and then
sync the LED brightnesses.

If you wanted to control a single LED for notifications the user space may have to do

echo 0 > blue/brightness
echo 0 > green/brightness
echo 255 > red/brightness
echo 1 > sync

As opposed to just
echo 255 > red/brightness

But if that is not a concern then removing the sync_enable is fine with me from a code standpoint
but not from a user space side.

Dan

> 									Pavel
> 

-- 
------------------
Dan Murphy