linux-kernel - Re: [PATCH v2 0/9] Add support for Microsoft Surface System Aggregator Module

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Message-ID: <20201206114153.GD693271@unreal>
Date:   Sun, 6 Dec 2020 13:41:53 +0200
From:   Leon Romanovsky <leon@...nel.org>
To:     Hans de Goede <hdegoede@...hat.com>
Cc:     Maximilian Luz <luzmaximilian@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, Mark Gross <mgross@...ux.intel.com>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Barnabás Pőcze <pobrn@...tonmail.com>,
        Arnd Bergmann <arnd@...db.de>, Rob Herring <robh@...nel.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Jonathan Corbet <corbet@....net>,
        Blaž Hrastnik <blaz@...n.io>,
        Dorian Stoll <dorian.stoll@...p.io>,
        platform-driver-x86@...r.kernel.org, linux-serial@...r.kernel.org,
        linux-acpi@...r.kernel.org, linux-kbuild@...r.kernel.org,
        linux-doc@...r.kernel.org
Subject: Re: [PATCH v2 0/9] Add support for Microsoft Surface System
 Aggregator Module

On Sun, Dec 06, 2020 at 11:41:46AM +0100, Hans de Goede wrote:
> Hi,
>
> On 12/6/20 11:33 AM, Leon Romanovsky wrote:
> > On Sun, Dec 06, 2020 at 11:04:06AM +0100, Hans de Goede wrote:
>
> <snip>
>
> >> But there is a difference between being careful and just nacking
> >> it because no new UAPI may be added at all (also see GKH's response).
> >
> > I saw, the author misunderstood the Greg's comments.
>
> Quoting from patch 8/9:
>
> "
> +==============================
> +User-Space EC Interface (cdev)
> +==============================
> +
> +The ``surface_aggregator_cdev`` module provides a misc-device for the SSAM
> +controller to allow for a (more or less) direct connection from user-space to
> +the SAM EC. It is intended to be used for development and debugging, and
> +therefore should not be used or relied upon in any other way. Note that this
> +module is not loaded automatically, but instead must be loaded manually.
> "
>
> If I'm not mistaken that seems to be pretty much what Greg asked for.

Right, unless you forget the end of his request.
 "
  The "joy" of creating a user api is that no matter how much you tell
  people "do not depend on this", they will, so no matter the file being
  in debugfs, or a misc device, you might be stuck with it for forever,
  sorry.
 "

So I still think that exposing user api for a development and debug of device
that has no future is wrong thing to do.

Thanks

>
> Regards,
>
> Hans
>