linux-kernel - Re: [PATCH 1/2] Add a common struct clk

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Message-ID: <20110110110028.GB12552@n2100.arm.linux.org.uk>
Date:	Mon, 10 Jan 2011 11:00:29 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Sascha Hauer <s.hauer@...gutronix.de>
Cc:	Jeremy Kerr <jeremy.kerr@...onical.com>,
	Ben Herrenchmidt <benh@...nel.crashing.org>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
Subject: Re: [PATCH 1/2] Add a common struct clk

On Mon, Jan 10, 2011 at 11:41:22AM +0100, Sascha Hauer wrote:
> This branch must be reworked because the correct locking is missing, but
> the first branch should be ready for merging once your clk-common
> patches are merged. I'll post the patches for review soon. I hope it's
> clear soon that your clk-common patches get merged.

Unless the locking problems can be resolved, the patches aren't ready.

>From what I've seen there's still quite a problem with what kind of
lock to use in the clock - mutex or spinlock.

I don't see that having some clocks be one and others another is really
acceptable - think about the resulting mess if you end up with some
parent mux'd clocks which are a mutex and others which are a spinlock.
Can a driver use an atomic call for that?  Sometimes depending on the
mux, sometimes depending on whether a parent clock is already enabled.

What if your clock was enabled while the mux selected another spinlock-
locked clk, but then you switched to a different operating point and the
mux then selected the mutex-locked clock.

We could say that this is illegal - but then we need to have the code
explicitly check this otherwise such situations will be created.
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