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Date: Wed, 2 Feb 2011 11:31:53 +0900
From: Jassi Brar <jassisinghbrar@...il.com>
To: Russell King - ARM Linux <linux@....linux.org.uk>
Cc: Uwe Kleine-König
<u.kleine-koenig@...gutronix.de>,
Jeremy Kerr <jeremy.kerr@...onical.com>,
Nicolas Pitre <nicolas.pitre@...aro.org>,
Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
linux-sh@...r.kernel.org,
Ben Herrenschmidt <benh@...nel.crashing.org>,
Sascha Hauer <s.hauer@...gutronix.de>,
Paul Mundt <lethal@...ux-sh.org>, linux-kernel@...r.kernel.org,
Dima Zavin <dmitriyz@...gle.com>,
Saravana Kannan <skannan@...eaurora.org>,
Ben Dooks <ben-linux@...ff.org>,
Vincent Guittot <vincent.guittot@...aro.org>,
linux-arm-kernel@...ts.infradead.org
Subject: Re: Locking in the clk API, part 2: clk_prepare/clk_unprepare
2011/2/2 Russell King - ARM Linux <linux@....linux.org.uk>:
> On Tue, Feb 01, 2011 at 04:22:03PM +0100, Uwe Kleine-König wrote:
>> Full ack. (I wonder if you misunderstood me or wanted to put my
>> statement into more words. Jassi didn't like that a clk_enable without
>> a previous clk_prepare worked on some platforms and on others it
>> doesn't. With BUG_ON(clk->ops->prepare && !clk->prepare_count) in
>> clk_enable we have exactly this situation.)
>
> Even with a NULL clk->ops->prepare function, we still want drivers to
> have called clk_prepare(). So we can do something like:
>
> if (WARN_ON(clk->prepare_count == 0))
> return -EINVAL;
>
> in clk_enable() should be sufficient and noisy enough not to be missed.
>
> I'd avoid BUG_ON() here as that will take the system down, which may
> increase the chances of getting useful bug reports.
Having thought about it, I think it's not necessary to immediately catch
drivers that work on some platforms and not on others -- a mere comment
'please add clk_prepare' during code review or a patch adding 'clk_prepare'
later upon stumbling across a platform on which the driver doesn't work,
should be OK. Let us not fret about it.
That leaves us with only having to ensure that :-
a) No two calls to clk_prepare/unprepare _hooks_ are consecutive.
b) clk_prepare is done on the clock (not necessarily by the driver
under consideration) before calls to clk_enable.
I think (a) is already easily managed by having the prepare_count,
and (b) can be reasonably managed by what Russell suggests above.
So, FWIW, I am for the idea.
Njoi!
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