linux-kernel - sysfs deferred

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Message-ID: <CAL_JsqLSfv4sbb9NRCTUOGu9vwEtE4buWUpcP58tZSxggcy08Q@mail.gmail.com>
Date:   Thu, 12 Jan 2017 11:27:01 -0600
From:   Rob Herring <robh@...nel.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Ben Hutchings <ben.hutchings@...ethink.co.uk>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Mark Brown <broonie@...nel.org>,
        Tomeu Vizoso <tomeu.vizoso@...labora.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Thierry Reding <thierry.reding@...il.com>
Subject: sysfs deferred_probe attribute

I just noticed that we have a new device attribute 'deferred_probe'
added in 4.10 with this commit:

commit 6751667a29d6fd64afb9ce30567ad616b68ed789
Author: Ben Hutchings <ben.hutchings@...ethink.co.uk>
Date:   Tue Aug 16 14:34:18 2016 +0100

    driver core: Add deferred_probe attribute to devices in sysfs

    It is sometimes useful to know that a device is on the deferred probe
    list rather than, say, not having a driver available.  Expose this
    information to user-space.

    Signed-off-by: Ben Hutchings <ben.hutchings@...ethink.co.uk>
    Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

It seems like a bad idea to add an ABI for an internal kernel feature.
When/if we replace deferred probe with something better based on
functional dependencies are we going to keep this attr around? Or
remove it and assume no userspace uses it? Perhaps it should be hidden
behind CONFIG_DEBUG or just make a debugfs file that lists the
deferred list. Then you wouldn't have to hunt for what got deferred.

Rob