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

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Date:   Mon, 16 May 2022 08:49:03 -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" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1] driver core: Extend deferred probe timeout on driver registration

On Fri, May 13, 2022 at 12:26 PM Saravana Kannan <saravanak@...gle.com> wrote:
>
> On Fri, May 13, 2022 at 6:58 AM Rob Herring <robh@...nel.org> wrote:
> >
> > 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?
>
> If it's the one where ip autoconfig was timing out, then John Stultz
> fixed it by fixing wait_for_device_probe().
> https://lore.kernel.org/all/20200422203245.83244-4-john.stultz@linaro.org/

Yeah, that was it.

Acked-by: Rob Herring <robh@...nel.org>