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

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Date:   Sat, 7 Jul 2018 17:58:11 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Rob Herring <robh@...nel.org>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Alexander Graf <agraf@...e.de>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Kevin Hilman <khilman@...nel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Joerg Roedel <joro@...tes.org>,
        Robin Murphy <robin.murphy@....com>,
        Mark Brown <broonie@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        boot-architecture@...ts.linaro.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v3 1/6] driver core: allow stopping deferred probe after
 init

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@...e.de>
> Signed-off-by: Rob Herring <robh@...nel.org>

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

Can you rebase it and resend?

thanks,

greg k-h