linux-kernel - Re: [PATCH v2 3/4] driver core: Add fw_devlink.timeout param to stop waiting for devlinks

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Message-ID: <CANDhNCr7ZwbCDK1ftigLK_S2qASj1yfenUG1WPaiYbjr5M9x3w@mail.gmail.com>
Date:   Thu, 17 Nov 2022 11:07:52 -0800
From:   John Stultz <jstultz@...gle.com>
To:     Javier Martinez Canillas <javierm@...hat.com>
Cc:     linux-kernel@...r.kernel.org,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Douglas Anderson <dianders@...omium.org>,
        Saravana Kannan <saravanak@...gle.com>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        linux-arm-msm@...r.kernel.org,
        Peter Robinson <pbrobinson@...hat.com>,
        Steev Klimaszewski <steev@...i.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Enric Balletbo i Serra <eballetbo@...hat.com>,
        Bjorn Andersson <andersson@...nel.org>,
        Brian Masney <bmasney@...hat.com>,
        Rob Herring <robh@...nel.org>
Subject: Re: [PATCH v2 3/4] driver core: Add fw_devlink.timeout param to stop
 waiting for devlinks

On Wed, Nov 16, 2022 at 4:02 AM Javier Martinez Canillas
<javierm@...hat.com> wrote:
>
> Currently, the probe deferral timeout does two things:
>
> 1) Call to fw_devlink_drivers_done() to relax the device dependencies and
>    allow drivers to be probed if these dependencies are optional.
>
> 2) Disable the probe deferral mechanism so that drivers will fail to probe
>    if the required dependencies are not present, instead of adding them to
>    the deferred probe pending list.
>
> But there is no need to couple these two, for example the probe deferral
> can be used even when the device links are disable (i.e: fw_devlink=off).
>
> So let's add a separate fw_devlink.timeout command line parameter to allow
> relaxing the device links and prevent drivers to wait for these to probe.

I'm probably being dim, but it's not immediately clear from this
description *why* this is useful. Maybe add some words on the tangible
benefit of splitting this up?

I'd also push a little bit back on why we need to split this into a
separate boot option. Since it's not obvious as to when a user would
want to use fw_devlink.timeout vs probe_deferral_timeout.
The extra complexity of remembering which timeout is for what might
become a burden to users and developers.

>
> +       fw_devlink.timeout=
> +                       [KNL] Debugging option to set a timeout in seconds for
> +                       drivers to give up waiting on dependencies and to probe
> +                       these are optional. A timeout of 0 will timeout at the
> +                       end of initcalls. If the time out hasn't expired, it'll
> +                       be restarted by each successful driver registration.
> +

This sounds pretty close to like the deferred_probe_timeout option.
I'd suggest some words to make the distinction more clear.

thanks
-john