linux-kernel - Re: [RFC PATCH 0/9] Add support for Microsoft Surface System Aggregator Module

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Date:   Wed, 23 Sep 2020 21:43:12 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Maximilian Luz <luzmaximilian@...il.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-serial@...r.kernel.org,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Rob Herring <robh@...nel.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>,
        Blaž Hrastnik <blaz@...n.io>,
        Dorian Stoll <dorian.stoll@...p.io>
Subject: Re: [RFC PATCH 0/9] Add support for Microsoft Surface System
 Aggregator Module

On Wed, Sep 23, 2020 at 5:43 PM Maximilian Luz <luzmaximilian@...il.com> wrote:
>
> On 9/23/20 5:30 PM, Arnd Bergmann wrote:
> > On Wed, Sep 23, 2020 at 5:15 PM Maximilian Luz <luzmaximilian@...il.com> wrote:
> >>
> >> Hello,
> >>
> >> The Surface System Aggregator Module (we'll refer to it as Surface
> >> Aggregator or SAM below) is an embedded controller (EC) found on various
> >> Microsoft Surface devices. Specifically, all 4th and later generation
> >> Surface devices, i.e. Surface Pro 4, Surface Book 1 and later, with the
> >> exception of the Surface Go series and the Surface Duo. Notably, it
> >> seems like this EC can also be found on the ARM-based Surface Pro X [1].
> >
> > I think this should go to drivers/platform/x86 or drivers/platform/surface/
> > along with other laptop vendor specific code rather than drivers/misc/.
>
> I initially had this under drivers/platform/x86. There are two main
> reasons I changed that: First, I think it's a bit too big for
> platform/x86 given that it basically introduces a new subsystem. At this
> point it's really less of "a couple of odd devices here and there" and
> more of a bus-type thing. Second, with the possibility of future support
> for ARM devices (Pro X, Pro X 2 which is rumored to come out soon), I
> thought that platform/x86 would not be a good fit.

I don't see that as a strong reason against it. As you write yourself, the
driver won't work on the arm machines without major changes anyway,
and even if it does, it fits much better with the rest of it.

If you are worried about the size of the directory,
drivers/platform/x86/surface/
would also work.

> I'd be happy to move this to platform/surface though, if that's
> considered a better fit and you're okay with me adding that. Would make
> sense given that there's already a platform/chrome, which, as far as I
> can tell, also seems to be mainly focused on EC support.

Yes, I think the main question is how much overlap you see functionally
between this driver and the others in drivers/platform/x86.

      Arnd