Message-ID: <20151019153548.GM32532@n2100.arm.linux.org.uk>
Date:	Mon, 19 Oct 2015 16:35:49 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Tomeu Vizoso <tomeu.vizoso@...labora.com>
Cc:	Mark Brown <broonie@...nel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Rob Herring <robh+dt@...nel.org>,
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Subject: Re: [GIT PULL] On-demand device probing

On Mon, Oct 19, 2015 at 05:00:54PM +0200, Tomeu Vizoso wrote:
> On 19 October 2015 at 16:30, Russell King - ARM Linux
> <linux@....linux.org.uk> wrote:
> > I typically see one or two, maybe five maximum on the platforms I have
> > here, but normally zero.
> 
> Hmm, I have given a look at our lava farm and have seen 2 dozens as
> common (with multi_v7).

No, because the lava farms tend not to be public.

> > What you can do is print those devices which have failed to probe at
> > late_initcall() time - possibly augmenting that with reports from
> > subsystems showing what resources are not available, but that's only
> > a guide, because of the "it might or might not be in a kernel module"
> > problem.
> 
> Well, adding those reports would give you a changelog similar to the
> one in this series...

I'm not sure about that, because what I was thinking of is adding
a flag which would be set at late_initcall() time prior to running
a final round of deferred device probing.

This flag would then be used in a deferred_warn() printk function
which would normally be silent, but when this flag is set, it would
print the reason for the deferral - and this would replace (or be
added) to the subsystems and drivers which return -EPROBE_DEFER.

That has the effect of hiding all the deferrals up until just before
launching into userspace, which should then acomplish two things -
firstly, getting rid of the rather useless deferred messages up to
that point, and secondly printing the reason why the remaining
deferrals are happening.

That should be a small number of new lines plus a one-line change
in subsystems and drivers.

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