linux-kernel - Re: sysfs deferred

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Date:   Thu, 12 Jan 2017 18:26:11 +0000
From:   Ben Hutchings <ben.hutchings@...ethink.co.uk>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Rob Herring <robh@...nel.org>,
        "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: Re: sysfs deferred_probe attribute

On Thu, 2017-01-12 at 18:41 +0100, Greg Kroah-Hartman wrote:
> On Thu, Jan 12, 2017 at 11:27:01AM -0600, Rob Herring wrote:
> > 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?

It should be removed then (and replaced with some kind of representation
of dependencies).

> > 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.
> 
> Ah, debugfs would be nice, I'd much prefer that.  I don't know how Ben
> is using this, but I think that would make more sense to me.

I'm not using it any programmatic way, and don't intend to.  debugfs
would be OK, but attaching it to devices was easy to do and seemed to
make sense.

Ben.

-- 
Ben Hutchings
Software Developer, Codethink Ltd.