linux-kernel - Re: Locking in the clk API

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Date:	Sat, 15 Jan 2011 15:15:07 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
Cc:	Christer Weinigel <christer@...nigel.se>,
	Saravana Kannan <skannan@...eaurora.org>,
	Jeremy Kerr <jeremy.kerr@...onical.com>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	linux-sh@...r.kernel.org,
	Ben Herrenschmidt <benh@...nel.crashing.org>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: Locking in the clk API

On Sat, Jan 15, 2011 at 04:03:31PM +0100, Uwe Kleine-König wrote:
> Hi Russell,
> 
> On Sat, Jan 15, 2011 at 02:53:58PM +0000, Russell King - ARM Linux wrote:
> > We've been around returning EAGAIN, WARN_ONs, BUG_ONs, having clk_enable()
> > vs clk_enable_atomic(), clk_enable_cansleep() vs clk_enable(), etc.
> > 
> > There's been a lot of talk on this issue for ages with no real progress
> > that I'm just going to repeat: let's unify those implementations which
> > use a spinlock for their clks into one consolidated solution, and
> > a separate consolidated solution for those which use a mutex.
> > 
> > This will at least allow us to have _some_ consolidation of the existing
> > implementations - and it doesn't add anything to the problem at hand.
> > It might actually help identify what can be done at code level to resolve
> > this issue.
> Great, so how should we do it?  Take Jeremy's patch and make the
> differenciation between sleeping and atomic implementation a Kconfig
> variable?

No - I've been suggesting for about a week now about doing two entirely
separate consolidations.

I think it would be insane to do the consolidation of the two different
implementations in one patch or even one patch set.  There needs to be
a consolidation of spinlock-based clks as one patch set, which is
entirely separate and independent from the consolidation of mutex-based
clks.

What if one of the consolidations turns out to be a problem?  Do we want
to throw both out, or do we want to keep as much as we possibly can?
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