linux-kernel - Re: [PATCH v2 2/2] gpio: gpio-adg1414: New driver

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Message-ID: <880631da17a6d8ed4afe5a8c453fd4f7d0e4fca5.camel@gmail.com>
Date: Fri, 14 Feb 2025 13:17:38 +0000
From: Nuno Sá <noname.nuno@...il.com>
To: Linus Walleij <linus.walleij@...aro.org>, Kim Seer Paller
	 <kimseer.paller@...log.com>
Cc: Bartosz Golaszewski <brgl@...ev.pl>, Rob Herring <robh@...nel.org>, 
 Krzysztof Kozlowski
	 <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	linux-gpio@...r.kernel.org, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] gpio: gpio-adg1414: New driver

Hi Linus,

On Fri, 2025-02-14 at 00:25 +0100, Linus Walleij wrote:
> Hi Kim,
> 
> thanks for your patch!
> 
> On Thu, Feb 13, 2025 at 2:17 PM Kim Seer Paller
> <kimseer.paller@...log.com> wrote:
> 
> > The ADG1414 is a 9.5 Ω RON ±15 V/+12 V/±5 V iCMOS Serially-Controlled
> > Octal SPST Switches
> > 
> > Signed-off-by: Kim Seer Paller <kimseer.paller@...log.com>
> 
> OK so I looked at the data sheet and it looks like this:
> 
> A  o-------/ --------o B
> 
> It'a a switch.
> 
> Why is this switch a "gpio", other than that it is convenient
> to use the GPIO abstraction to control it?
> 
> GPIO is usually devices that can drive a line high or low.
> This is very far from that. This could switch some analog
> line or whatever, right?

I would say so yes but Kim should know better...
> 
> Now, the kernel does not have switch subsystem I think,
> so this is something like a special case, so we might be
> compelled to make an exception, if the users will all be in

Exactly, since we could not find anything, the best fit seemed like the gpio
subsystem. I was the one suggesting it since a new subsystem for a simple device
like this looked excessive. If we had more devices that would fit such a class
of devices, maybe it would make more sense to start thinking on such a
subsystem?

> say userspace and make use of this switch for factory lines
> or similar.

Kim should know better again (about usecases) but I would also assume this is
for userspace use.

Thanks!
- Nuno Sá