linux-kernel - Re: [RFC,PATCH 1/3] Add a common struct clk

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Message-ID: <20110210104639.GZ27982@pengutronix.de>
Date:	Thu, 10 Feb 2011 11:46:39 +0100
From:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
To:	Richard Zhao <richard.zhao@...escale.com>
Cc:	Ryan Mallon <ryan@...ewatersys.com>,
	Nicolas Pitre <nicolas.pitre@...aro.org>,
	Dima Zavin <dmitriyz@...gle.com>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	linux-sh@...r.kernel.org,
	Ben Herrenschmidt <benh@...nel.crashing.org>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	linux-kernel@...r.kernel.org, Paul Mundt <lethal@...ux-sh.org>,
	Saravana Kannan <skannan@...eaurora.org>,
	Ben Dooks <ben-linux@...ff.org>,
	Russell King <linux@....linux.org.uk>,
	Jeremy Kerr <jeremy.kerr@...onical.com>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [RFC,PATCH 1/3] Add a common struct clk

Hello,

On Thu, Feb 10, 2011 at 06:03:19PM +0800, Richard Zhao wrote:
> On Thu, Feb 10, 2011 at 09:21:14AM +1300, Ryan Mallon wrote:
> > On 02/09/2011 07:41 PM, Jeremy Kerr wrote:
> > 
> > Hi Jeremy,
> > 
> > Couple more comments below.
> > 
> > ~Ryan
> > 
> [...]
> > > +int clk_enable(struct clk *clk)
> > > +{
> > > +     unsigned long flags;
> > > +     int ret = 0;
> > > +
> > > +     spin_lock_irqsave(&clk->enable_lock, flags);
> > 
> >         WARN_ON(clk->prepare_count == 0); ?
> > 
> > > +     if (clk->enable_count == 0 && clk->ops->enable)
> > > +             ret = clk->ops->enable(clk);
> > 
> > Does it make sense to have a clock with no enable function which still
> > returns success from clk_enable? Do we have any platforms which have
> > NULL clk_enable functions?
> > 
> > I think that for enable/disable at least we should require platforms to
> > provide functions and oops if they have failed to do so. In the rare
> > case that a platform doesn't need to do anything for enable/disable they
> > can just supply empty functions.
> It's possible to be NULL. So are set_rate/get_rate.
> Ideally, if it's NULL: 
> prepare/unprepare: only call parent's prepare/unprepare
> enable/disable: only call parent's enable/disable
> set_rate: fail
> get_rate: reture parent's get_rate
> set_parent: fail
> get_parent: fail
I wouldn't hard-code the parents into the generic functions.  But I
suggest to provide generic callbacks to do this, e.g.

clk_get_rate_from_parent(struct clk *c)
{
	struct clk *parent = clk_get_parent(c);

	return clk_get_rate(parent);
}

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
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