linux-kernel - Re: [PATCH v5] platform/chrome: wilco_ec: Add telemetry char device interface

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Message-ID: <CAHX4x86QbUybRoMScsJ+vwzic6TfECzBnccEe89M8HojMDgH8Q@mail.gmail.com>
Date:   Fri, 24 May 2019 08:47:51 -0600
From:   Nick Crews <ncrews@...omium.org>
To:     Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        Dmitry Torokhov <dtor@...gle.com>
Cc:     Benson Leung <bleung@...omium.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Duncan Laurie <dlaurie@...omium.org>,
        Daniel Kurtz <djkurtz@...omium.org>,
        Simon Glass <sjg@...omium.org>, bartfab@...omium.org,
        Oleh Lamzin <lamzin@...gle.com>,
        Jason Wong <jchwong@...gle.com>
Subject: Re: [PATCH v5] platform/chrome: wilco_ec: Add telemetry char device interface

Hey Enric, thanks for the review!

On Fri, May 24, 2019 at 3:51 AM Enric Balletbo i Serra
<enric.balletbo@...labora.com> wrote:
>
> Hi Nick,
>
> I'm mostly fine with it but ...
>
> On 21/5/19 21:20, Nick Crews wrote:
> > The Wilco Embedded Controller is able to send telemetry data
> > which is useful for enterprise applications. A daemon running on
> > the OS sends a command to the EC via a write() to a char device,
> > and can read the response with a read(). The write() request is
> > verified by the driver to ensure that it is performing only one
> > of the whitelisted commands, and that no extraneous data is
> > being transmitted to the EC. The response is passed directly
> > back to the reader with no modification.
> >
> > The character device will appear as /dev/wilco_telemN, where N
> > is some small non-negative integer, starting with 0. Only one
>
> Still remains my question in the previous version.
>
> We will really have more than one /dev/wilco_telemN devices handled by this
> driver? Why not use a Miscellaneous Character Device Driver that will simplify
> the code?

We probably will not have more than one device handled by the driver,
but I did this
at the request of Dmitry. He wanted to just do it right the first time so no one
would have to fix it if in the future a second device was needed. FYI,
I did the same
thing for the events driver at https://lore.kernel.org/patchwork/patch/1078461/.

I just tried to find the email thread and/or the review on the
Chromium Gerrit that
documents this, but I couldn't find it. It must have been a private
message, so sorry I
can't link you to it.

Dmitry, am I interpreting your reasoning correctly?

Thanks,
Nick