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

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Date:	Thu, 10 Feb 2011 18:03:19 +0800
From:	Richard Zhao <richard.zhao@...escale.com>
To:	Ryan Mallon <ryan@...ewatersys.com>
CC:	Jeremy Kerr <jeremy.kerr@...onical.com>,
	Nicolas Pitre <nicolas.pitre@...aro.org>,
	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>,
	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>,
	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>,
	Russell King <linux@....linux.org.uk>,
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [RFC,PATCH 1/3] Add a common struct clk

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

Thanks
Richard
> 
> > +
> > +     if (!ret)
> > +             clk->enable_count++;
> > +     spin_unlock_irqrestore(&clk->enable_lock, flags);
> > +
> > +     return ret;
> > +}
> > +EXPORT_SYMBOL_GPL(clk_enable);
> > +

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