linux-kernel - Re: Locking in the clk API

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Message-ID: <4D2D09E2.5030305@codeaurora.org>
Date:	Tue, 11 Jan 2011 17:54:42 -0800
From:	Saravana Kannan <skannan@...eaurora.org>
To:	Paul Mundt <lethal@...ux-sh.org>
CC:	Jeremy Kerr <jeremy.kerr@...onical.com>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	linux-sh@...r.kernel.org,
	Ben Herrenschmidt <benh@...nel.crashing.org>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	linux-kernel@...r.kernel.org,
	Uwe Kleine-K?nig <u.kleine-koenig@...gutronix.de>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: Locking in the clk API

On 01/11/2011 04:18 AM, Paul Mundt wrote:
> Again, you are approaching it from the angle that an atomic clock is a
> special requirement rather than the default behaviour. Sleeping for
> lookup, addition, and deletion are all quite acceptable, but
> enable/disable pairs have always been intended to be usable from atomic
> context. Anyone that doesn't count on that fact is either dealing with
> special case clocks (PLLs, root clocks, etc.) or simply hasn't bothered
> implementing any sort of fine grained runtime power management for their
> platform.

Paul,

I see you repeating this point a couple of times and I'm a bit confused 
how you handle the clock tree/dependencies.

Does your clock driver NOT hide the details of what root clock/PLL a 
branch clock is sourced from? If you do hide the details of the root/PLL 
source, how do you get the branch clk_enable() to be done atomically if 
the root/PLL enables are not possible in atomic context?

Is it simply a matter of your hardware having PLLs and root clocks that 
can be turned on/off quickly?

-Saravana

-- 
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