linux-kernel - Re: Locking in the clk API

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Message-Id: <201101112235.43061.jeremy.kerr@canonical.com>
Date:	Tue, 11 Jan 2011 22:35:42 +0800
From:	Jeremy Kerr <jeremy.kerr@...onical.com>
To:	Paul Mundt <lethal@...ux-sh.org>
Cc:	"Russell King - ARM Linux" <linux@....linux.org.uk>,
	linux-sh@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	Ben Herrenschmidt <benh@...nel.crashing.org>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	"Uwe Kleine-König" 
	<u.kleine-koenig@...gutronix.de>
Subject: Re: Locking in the clk API

Hi Paul,

> Again, you are approaching it from the angle that an atomic clock is a
> special requirement rather than the default behaviour.

I'm not considering it a special requirement, but it's still a requirement 
(that the called function does not sleep).

The problem with the inverse logic (clk_enable/clk_enable_sleepable) is that 
now you've made the caller need to know what kind of clock it has, or might 
have one day.

 * For clk_enable/clk_enable_atomic, the decision is: is this call in an
   atomic context?

 * For clk_enable/clk_enable_sleepable, the decision is: might the clock code
   have given us a sleeping clock?

Note that it's much easier to guarantee correctness for the first than it is 
for the second.

Cheers,

Jeremy
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