linux-kernel - Re: [PATCH 1/1] platform/x86: revert pcengines-apuv2 wire up simswitch gpio as led

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Message-ID: <e95c8b76-cfaf-4d49-aa93-525093e61e03@metux.net>
Date:   Fri, 31 Jul 2020 16:01:45 +0200
From:   "Enrico Weigelt, metux IT consult" <lkml@...ux.net>
To:     Florian Eckert <fe@....tdt.de>, info@...ux.net,
        vhart@...radead.org, andy@...radead.org,
        Eckert.Florian@...glemail.com
Cc:     platform-driver-x86@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] platform/x86: revert pcengines-apuv2 wire up
 simswitch gpio as led

On 31.07.20 15:45, Enrico Weigelt, metux IT consult wrote:

Addendum: there's even more functionality we'll loose

Individual LED lines can be made available to specific
unprivileged users / processes, eg. chmod or passing fd's.

For example, allowing a web application to pull the switch,
w/o ever becoming root. And that's indeed a practial use case,
which is used in the field.

--mtx


> On 13.07.20 10:50, Florian Eckert wrote:
> 
> Hello Florian,
> 
>> This reverts commit 5037d4ddda31c2dbbb018109655f61054b1756dc.
> 
> no, please dont.
> 
>> This change connects the simswap to the LED subsystem of the kernel.
>> From my point of view, it's nonsense. If we do it this way, then this
>> can be switched relatively easily via the LED subsystem (trigger:
>> none/default-on) and that is dangerous! If this is used, it would be
>> unfavorable, since there is also another trigger (trigger:
>> heartbeat/netdev).
> 
> I don't think that potential silly abuse is a good argument. It if
> would, we should also disallow things like "echo FOO > /dev/sda" :p
> 
> The reason for it wire'ing up was having an simple and easy to use
> interface. Raw gpios do NOT meet this criteria: complicated to use and
> not stable addressing (from userland PoV) - would require an extra
> userland program just for that single specific task.
> 
> Yes, LED is not the optimal approach, same for other gpio-connected
> switches, eg. relais or various multiplexers. But as long as we don't
> have a really fitting subsystem, it's IMHO the best compromise we have
> so far.
> 
> Actually, I've already been hacking on a better subsystem, which models
> switchable inter-device connections. It's called portmux. But it's not
> usable yet. Lets talk about this instead of just wildly dropping
> existing functionality, that's used in the field.
> 
> 
> --mtx
> 

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Enrico Weigelt, metux IT consult
Free software and Linux embedded engineering
info@...ux.net -- +49-151-27565287