linux-kernel - Re: [PATCH v1] driver core: Extend deferred probe timeout on driver registration

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Date:   Fri, 13 May 2022 08:58:11 -0500
From:   Rob Herring <robh@...nel.org>
To:     Saravana Kannan <saravanak@...gle.com>
Cc:     Jonathan Corbet <corbet@....net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Linus Walleij <linus.walleij@...aro.org>,
        Will Deacon <will@...nel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Kevin Hilman <khilman@...nel.org>,
        Thierry Reding <treding@...dia.com>,
        Mark Brown <broonie@...nel.org>, Pavel Machek <pavel@....cz>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
        Paul Kocialkowski <paul.kocialkowski@...tlin.com>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        "open list:THERMAL" <linux-pm@...r.kernel.org>,
        Linux IOMMU <iommu@...ts.linux-foundation.org>,
        Android Kernel Team <kernel-team@...roid.com>,
        Linux Doc Mailing List <linux-doc@...r.kernel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] driver core: Extend deferred probe timeout on driver registration

On Fri, Apr 29, 2022 at 5:09 PM Saravana Kannan <saravanak@...gle.com> wrote:
>
> The deferred probe timer that's used for this currently starts at
> late_initcall and runs for driver_deferred_probe_timeout seconds. The
> assumption being that all available drivers would be loaded and
> registered before the timer expires. This means, the
> driver_deferred_probe_timeout has to be pretty large for it to cover the
> worst case. But if we set the default value for it to cover the worst
> case, it would significantly slow down the average case. For this
> reason, the default value is set to 0.
>
> Also, with CONFIG_MODULES=y and the current default values of
> driver_deferred_probe_timeout=0 and fw_devlink=on, devices with missing
> drivers will cause their consumer devices to always defer their probes.
> This is because device links created by fw_devlink defer the probe even
> before the consumer driver's probe() is called.
>
> Instead of a fixed timeout, if we extend an unexpired deferred probe
> timer on every successful driver registration, with the expectation more
> modules would be loaded in the near future, then the default value of
> driver_deferred_probe_timeout only needs to be as long as the worst case
> time difference between two consecutive module loads.
>
> So let's implement that and set the default value to 10 seconds when
> CONFIG_MODULES=y.

We had to revert a non-zero timeout before (issue with NFS root IIRC).
Does fw_devlink=on somehow fix that?

Rob