linux-kernel - Re: [PATCH] regulator: Don't print error in devm_regulator_bulk_get() on -EPROBE

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Date:	Wed, 16 Mar 2016 08:19:42 -0300
From:	Javier Martinez Canillas <javier@....samsung.com>
To:	Mark Brown <broonie@...nel.org>
Cc:	linux-kernel@...r.kernel.org, Liam Girdwood <lgirdwood@...il.com>
Subject: Re: [PATCH] regulator: Don't print error in devm_regulator_bulk_get()
 on -EPROBE_DEFER

Hello Mark,

On 03/16/2016 06:59 AM, Mark Brown wrote:
> On Tue, Mar 15, 2016 at 05:35:14PM -0300, Javier Martinez Canillas wrote:
> 
>> The regulators may not be available just because their driver's probe was
>> not executed and the regulators were not registered yet. So don't print an
>> error in this case to avoid polluting the kernel log and confuse the users.
> 
> We've been through this repeatedly - this is the case for all probe
> deferrals and if we just don't print the errors at all then people won't
> be able to tell if they've got a missing dependency.  We need people to

I wonder if we can use a dev_dbg() then so it will be printed at debug level.
That way users can have that info if they want but not pollute the boot log.

Basically I want to get rid of things like this:

[    1.438422] exynos-hdmi 14530000.hdmi: Failed to get supply 'vdd': -517
[    1.443638] [drm:hdmi_probe] *ERROR* failed to get regulators
[    1.449326] [drm:hdmi_probe] *ERROR* hdmi_resources_init failed

The HDMI driver probed correctly but looking at the log it seems that things
failed so can mislead users not familiar with the probe deferral mechanism.

> work on things like allowing the kernel to make use of the dependency
> information it has to order probes more sensibly.
>

Agreed, I've seen Tomeu's patches and the following discussions.
 
> Raphael had some ideas he was talking about at Kernel Summit for this,
> Russell King also proposed just suppressing the errors until we're at
> the last deferred probe run at the end of init.
> 

Suppressing errors is a nice idea but will again lead to false positives
when the drivers are built as a module AFAICT.

Best regards,
-- 
Javier Martinez Canillas
Open Source Group
Samsung Research America