linux-kernel - Re: [PATCH] HID: logitech-hidpp: support Color LED feature (8071).

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Date:   Wed, 23 Mar 2022 21:28:02 -0600
From:   Manuel Schönlaub <manuel.schoenlaub@...il.com>
To:     Bastien Nocera <hadess@...ess.net>
Cc:     Filipe Laíns <lains@...eup.net>,
        jikos@...nel.org, benjamin.tissoires@...hat.com,
        linux-input@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] HID: logitech-hidpp: support Color LED feature (8071).

On Wed, Mar 23, 2022 at 11:24:18PM +0100, Bastien Nocera wrote:
> On Wed, 2022-03-23 at 21:22 +0000, Filipe Laíns wrote:
> > On Tue, 2022-03-08 at 16:50 -0700, Manuel Schönlaub wrote:
> > > The HID++ protocol allows to set multicolor (RGB) to a static
> > > color.
> > > Multiple of such LED zones per device are supported.
> > > This patch exports said LEDs so that they can be set from
> > > userspace.
> > > 
> > > Signed-off-by: Manuel Schönlaub <manuel.schoenlaub@...il.com>
> > > ---
> > >  drivers/hid/hid-logitech-hidpp.c | 188
> > > +++++++++++++++++++++++++++++++
> > >  1 file changed, 188 insertions(+)
> > 
> > *snip*
> > 
> > Hi Manuel,
> > 
> > Thanks for putting this forward, although I am not sure if this is
> > the best way
> > to handle this.
> > 
> > Before anything, could you elaborate a bit on what lead to you
> > wanting this?
> > 
> > There are a couple of reasons why merging this in the kernel might be
> > problematic.
> > 
> > 1) I don't think we will ever support the full capabilities of the
> > devices, so
> > configuration via userspace apps will always be required, and here we
> > are
> > introducing a weird line between the two.
> > 
> > 2) There is already an ecosystem of userspace configuration apps,
> > with which
> > this would conflict. They might not be in the best maintenance state
> > due to lack
> > of time from the maintainers, but moving this functionality to the
> > kernel, which
> > is harder change, and harder to ship to users, will only make that
> > worse.
> 
> There's already an API for LEDs in the kernel, why shouldn't it be used
> to avoid user-space needing to know how to configure Logitech, and
> every other brand of keyboards?
> 
> systemd has code to save and restore LED status, as well as code to
> change the level of backlight. I can imagine that it wouldn't take much
> to make it aware of RGB LEDs so it handles them properly, whether it's
> for Logitech, or another brand of keyboards, or laptops.

Teaching systemd-backlight about mulicolor backlights might be a nice project
too. But their use case seems to be more about screen backlights as it seems.
Did I overlook something here?

Oh and yeah, IMHO another argument could be that obviously at some point
the LED management could be removed from those user space tools, as the
kernel would already know about them.

After all the LED class devices should be there for a reason ;-)

Cheers,

Manuel