linux-kernel - Re: Locking in the clk API

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Message-ID: <20110115160329.GD6917@pengutronix.de>
Date:	Sat, 15 Jan 2011 17:03:29 +0100
From:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
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 03:15:07PM +0000, Russell King - ARM Linux wrote:
> 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 didn't read that out of your mails.
 
> 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.
I think they should share most of the code.  Apart from calling
different locking functions they should be pretty much identical, no?

> 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?
Do you really expect fundamental problems that make it necessary to
switch all platforms that use the (say) sleeping variant back to their
original implementation?  I don't think that when the general idea of
using clk_ops prooves for the atomic case it cannot happen that a
"native" implementation for a sleeping clk is better that a sleeping
clk_ops implementation.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
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