linux-kernel - Re: Locking in the clk API

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Message-ID: <4D38687A.6040307@fluff.org>
Date:	Thu, 20 Jan 2011 16:53:14 +0000
From:	Ben Dooks <ben-linux@...ff.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 11/01/11 12:18, Paul Mundt wrote:
> On Tue, Jan 11, 2011 at 06:30:18PM +0800, Jeremy Kerr wrote:
>> Hi Paul,
>>
>>> No, the sleeping clock case is and always will be a corner case, and I
>>> have no interest in pretending otherwise. On SH we have hundreds of
>>> clocks that are all usable in the atomic context and perhaps less than a
>>> dozen that aren't (and even in those cases much of the PLL negotiation is
>>> handled in hardware so there's never any visibility for the lock-down
>>> from the software side, other architectures also have similar behaviour).
>>
>> I'm not too worried about the corner-cases on the *implementation* side, more 
>> the corner-cases on the API side: are we seeing more users of the API that 
>> require an atomic clock, or more that don't care?
>>
> 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.

No, the API has always been defined to ensure clk_enable() returns once
a clock is running and usable, so if the case where there are PLLs in
the way is inconvenient to you, then sorry but they exist already.
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