driver core: Revert default driver_deferred_probe_timeout value to 0

This patch addresses a regression in 5.7-rc1+

In commit c8c43cee ("driver core: Fix
driver_deferred_probe_check_state() logic"), we both cleaned up
the logic and also set the default driver_deferred_probe_timeout
value to 30 seconds to allow for drivers that are missing
dependencies to have some time so that the dependency may be
loaded from userland after initcalls_done is set.

However, Yoshihiro Shimoda reported that on his device that
expects to have unmet dependencies (due to "optional links" in
its devicetree), was failing to mount the NFS root.

In digging further, it seemed the problem was that while the
device properly probes after waiting 30 seconds for any missing
modules to load, the ip_auto_config() had already failed,
resulting in NFS to fail. This was due to ip_auto_config()
calling wait_for_device_probe() which doesn't wait for the
driver_deferred_probe_timeout to fire.

Fixing that issue is possible, but could also introduce 30
second delays in bootups for users who don't have any
missing dependencies, which is not ideal.

So I think the best solution to avoid any regressions is to
revert back to a default timeout value of zero, and allow
systems that need to utilize the timeout in order for userland
to load any modules that supply misisng dependencies in the dts
to specify the timeout length via the exiting documented boot
argument.

Thanks to Geert for chasing down that ip_auto_config was why NFS
was failing in this case!

Cc: "David S. Miller" <davem@davemloft.net>
Cc: Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>
Cc: Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Rafael J. Wysocki <rjw@rjwysocki.net>
Cc: Rob Herring <robh@kernel.org>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Cc: Robin Murphy <robin.murphy@arm.com>
Cc: Andy Shevchenko <andy.shevchenko@gmail.com>
Cc: Sudeep Holla <sudeep.holla@arm.com>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Naresh Kamboju <naresh.kamboju@linaro.org>
Cc: Basil Eljuse <Basil.Eljuse@arm.com>
Cc: Ferry Toth <fntoth@gmail.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Anders Roxell <anders.roxell@linaro.org>
Reported-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Tested-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
Fixes: c8c43cee ("driver core: Fix driver_deferred_probe_check_state() logic")
Signed-off-by: John Stultz <john.stultz@linaro.org>
Link: https://lore.kernel.org/r/20200422203245.83244-2-john.stultz@linaro.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>