Date: Sun, 20 Feb 2011 13:13:09 +0000
From: Russell King - ARM Linux <linux@arm.linux.org.uk>
To: Saravana Kannan <skannan@codeaurora.org>
Cc: Jeremy Kerr <jeremy.kerr@canonical.com>,
        linux-arm-kernel@lists.infradead.org,
        Nicolas Pitre <nicolas.pitre@linaro.org>,
        Lorenzo Pieralisi <Lorenzo.Pieralisi@arm.com>,
        linux-sh@vger.kernel.org, Ben Herrenschmidt <benh@kernel.crashing.org>,
        Sascha Hauer <s.hauer@pengutronix.de>,
        Paul Mundt <lethal@linux-sh.org>, linux-kernel@vger.kernel.org,
        Dima Zavin <dmitriyz@google.com>, Ben Dooks <ben-linux@fluff.org>,
        Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= 
	<u.kleine-koenig@pengutronix.de>,
        Vincent Guittot <vincent.guittot@linaro.org>
Subject: Re: [RFC,PATCH 1/3] Add a common struct clk
Message-ID: <20110220131309.GF14495@n2100.arm.linux.org.uk>
References: <1297233693.242364.862698430999.1.gpush@pororo> <4D53749B.6010102@codeaurora.org> <201102151041.40655.jeremy.kerr@canonical.com> <4D5A100F.9000809@codeaurora.org>
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On Mon, Feb 14, 2011 at 09:33:03PM -0800, Saravana Kannan wrote:
> Assuming Russell and/or the community agrees on the semantics of  
> "parent", without the generic implementation grabbing the prepare_lock  
> while setting the parent, there is no way for the specific clock driver  
> implementations to cleanly ensure correctness. The only option for them  
> would be to peek into the generic clock struct and grab the prepare lock  
> -- to me that would be an ugly hack and/or layering violation that would  
> cause problems later on.
>
> Russell/All,
>
> What's the meaning of a parent clock? Do you agree with my definition --  
> "the parent clock is the clock that generates the clock signal from  
> which the child clock derives (divide, etc) it's clock signal from."? Or  
> is it open to interpretation by each implementation?

Your definition seems sane - I'm not sure what use a parent clock which
had nothing to do with a child would be.

As for the locking issue, I've no idea on that at the moment.  I don't
think implementations should grab the prepare lock, I think that's
something the generic code should take care of for clk_set_rate(),
clk_set_parent() etc.
--
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