linux-kernel - Re: ThinkPad T480s & LED_MUTE, LED

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Message-ID: <20180615233628.gy2ffgupctheyqof@khazad-dum.debian.net>
Date:   Fri, 15 Jun 2018 20:36:28 -0300
From:   Henrique de Moraes Holschuh <hmh@....eng.br>
To:     Pali Rohár <pali.rohar@...il.com>
Cc:     Pavel Machek <pavel@....cz>,
        Henrique de Moraes Holschuh <ibm-acpi@....eng.br>,
        ibm-acpi-devel@...ts.sourceforge.net,
        platform-driver-x86@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: ThinkPad T480s & LED_MUTE, LED_MICMUTE

On Fri, 15 Jun 2018, Pali Rohár wrote:
> This means that kernel should not export any led class device. Or when
> exported, then "set" operation should always fail.

"not export" is right.

> > 2. Otherwise implement it in-kernel, so that userspace cannot unmute
> >    when the human has activated the "mute" switch, and the LED cannot be
> >    controlled by userspace to lie (report mute when it is not mute).
> 
> This looks like a good candidate to use led "trigger" interface. Create
> a mute trigger and attach it to that led device.

Maybe, as long as done in-kernel and not possible to mess with from
userspace.

> means set. What is SHDA doing, I have not figured out. It does not

Look at the HDA mixer state, SHDA is likely to be directly messing with
it.

-- 
  Henrique Holschuh