Re: [PATCH v3 1/6] driver core: allow stopping deferred probe after init

From: Greg Kroah-Hartman
Date: Sat Jul 07 2018 - 11:58:28 EST

On Thu, Jun 28, 2018 at 02:43:39PM -0600, Rob Herring wrote:
> Deferred probe will currently wait forever on dependent devices to probe,
> but sometimes a driver will never exist. It's also not always critical for
> a driver to exist. Platforms can rely on default configuration from the
> bootloader or reset defaults for things such as pinctrl and power domains.
> This is often the case with initial platform support until various drivers
> get enabled. There's at least 2 scenarios where deferred probe can render
> a platform broken. Both involve using a DT which has more devices and
> dependencies than the kernel supports. The 1st case is a driver may be
> disabled in the kernel config. The 2nd case is the kernel version may
> simply not have the dependent driver. This can happen if using a newer DT
> (provided by firmware perhaps) with a stable kernel version. Deferred
> probe issues can be difficult to debug especially if the console has
> dependencies or userspace fails to boot to a shell.
> There are also cases like IOMMUs where only built-in drivers are
> supported, so deferring probe after initcalls is not needed. The IOMMU
> subsystem implemented its own mechanism to handle this using OF_DECLARE
> linker sections.
> This commit adds makes ending deferred probe conditional on initcalls
> being completed or a debug timeout. Subsystems or drivers may opt-in by
> calling driver_deferred_probe_check_init_done() instead of
> unconditionally returning -EPROBE_DEFER. They may use additional
> information from DT or kernel's config to decide whether to continue to
> defer probe or not.
> The timeout mechanism is intended for debug purposes and WARNs loudly.
> The remaining deferred probe pending list will also be dumped after the
> timeout. Not that this timeout won't work for the console which needs
> to be enabled before userspace starts. However, if the console's
> dependencies are resolved, then the kernel log will be printed (as
> opposed to no output).
> Cc: Alexander Graf <agraf@xxxxxxx>
> Signed-off-by: Rob Herring <robh@xxxxxxxxxx>

I wanted to apply this series, but this patch failed to apply to my
driver-core tree :(

Can you rebase it and resend?


greg k-h