linux-kernel - Re: [RFC PATCH 1/2] regmap: add configurable lock class key for lockdep

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Message-ID: <20150625144948.GO14071@sirena.org.uk>
Date:	Thu, 25 Jun 2015 15:49:48 +0100
From:	Mark Brown <broonie@...nel.org>
To:	Nicolas Boichat <drinkcat@...omium.org>
Cc:	Mauro Carvalho Chehab <mchehab@....samsung.com>,
	Antti Palosaari <crope@....fi>, Ingo Molnar <mingo@...hat.com>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Lars-Peter Clausen <lars@...afoo.de>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org, Bard Liao <bardliao@...ltek.com>,
	Oder Chiou <oder_chiou@...ltek.com>,
	Liam Girdwood <lgirdwood@...il.com>,
	Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai <tiwai@...e.de>,
	alsa-devel@...a-project.org,
	Anatol Pomozov <anatol.pomozov@...il.com>
Subject: Re: [RFC PATCH 1/2] regmap: add configurable lock class key for
 lockdep

On Thu, Jun 25, 2015 at 05:35:03PM +0800, Nicolas Boichat wrote:

> I'm trying to revive Antti's patch [1], as we are hitting similar issue
> with rt5677 driver. I only updated the commit message and documentation,
> I kept both Signed-off-by and From lines, with a small note highlighting
> my changes, let me know if that's not appropriate.

This continues to have the same problems as the previous version of the
patch where I can't really tell how users are supposed to figure out if
they should use this or not.  There will be cases where there is a clear
use within the driver itself but as far as I can tell almost any driver
might be bitten by this if some underlying driver on a given system
happens to use a regmap so should be allocating a class.

> One issue that was raised by Mark at the time is that a per-regmap_config
> lock class might not be enough (Mark mentioned clocks as an example). The
> current implementation should be good enough as long as the clock regmaps
> do not access each other. If this is a problem, maybe we should consider
> replacing lockdep_lock_class_key by a boolean use_own_lock_class that would
> allocate/use a per regmap instance lock class, or have devm_regmap_init
> take an extra parameter specifying the lock class.

I think this is a problem and making this something that every regmap
does by default was my original suggestion, there's also Arjan's
suggestion of just using nested mutexes rather than classes.

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