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

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Message-ID: <20110210130800.GB3316@richard-laptop>
Date:	Thu, 10 Feb 2011 21:08:00 +0800
From:	Richard Zhao <linuxzsc@...il.com>
To:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
Cc:	Richard Zhao <richard.zhao@...escale.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,
	Ryan Mallon <ryan@...ewatersys.com>,
	Dima Zavin <dmitriyz@...gle.com>,
	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

On Thu, Feb 10, 2011 at 11:46:39AM +0100, Uwe Kleine-König wrote:
> 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.
Why? what restriction will it cause to add parent in clk?
Two benifits at least I can see:
1. null ops handle, as I said above.
2. export clock tree to user level for debug. It's very helpfull.

Thanks
Richard
> 
> 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/  |
> 
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
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