Date:	Mon, 17 Oct 2011 16:48:52 +0800
From:	Richard Zhao <richard.zhao@...aro.org>
To:	Sascha Hauer <s.hauer@...gutronix.de>
CC:	<linux-arm-kernel@...ts.infradead.org>, <paul@...an.com>,
	<linaro-dev@...ts.linaro.org>, <linus.walleij@...ricsson.com>,
	<patches@...aro.org>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	<magnus.damm@...il.com>, <linux-kernel@...r.kernel.org>,
	<eric.miao@...aro.org>, <grant.likely@...retlab.ca>,
	<arnd.bergmann@...aro.org>, <dsaxena@...aro.org>,
	<tglx@...utronix.de>, <amit.kucheria@...aro.org>,
	<linux@....linux.org.uk>, <skannan@...cinc.com>,
	Mike Turquette <mturquette@...com>,
	<jeremy.kerr@...onical.com>, <shawn.guo@...escale.com>,
	<sboyd@...inc.com>
Subject: Re: [PATCH v2 1/7] clk: Add a generic clock infrastructure

On Sun, Oct 16, 2011 at 07:55:21PM +0200, Sascha Hauer wrote:
> On Fri, Oct 14, 2011 at 06:32:33PM +0800, Richard Zhao wrote:
> > On Fri, Oct 14, 2011 at 11:05:04AM +0100, Mark Brown wrote:
> > > On Fri, Oct 14, 2011 at 04:10:26PM +0800, Richard Zhao wrote:
> > > > On Thu, Sep 22, 2011 at 03:26:56PM -0700, Mike Turquette wrote:
> > > 
> > > snip essentially Mike's entire mail - *please* delete irrelevant quotes
> > > from your replies, it makes it very much easier to find the new text in
> > > your mail and is much more friendly to people reading mail on mobile
> > > devices.
> > I snip not enough? sorry for that. I'll be carefull.
> > > 
> > > > > +static int __clk_enable(struct clk *clk)
> > > > > +{
> > > 
> > > > Could you expose __clk_enable/__clk_disable? I find it hard to implement
> > > > clk group. clk group means, when a major clk enable/disable, it want a set
> > > > of other clks enable/disable accordingly.
> > > 
> > > Shouldn't this be something the core is implementing?  I'd strongly
> > > expect that the clock drivers are relatively dumb and delegate all the
> > > decision making to the core API.  Otherwise it's going to be hard for
> > > the core to implement any logic that involves working with more than one
> > > clock like rate change notification, or guarantee that driver requests
> > > made through the API are satisfied, as the state of the clocks will be
> > > changing underneath it.
> > From my point of view, the first step of generic clk can be, easy to adopt
> > features of clocks in current mainline git.
> > Back to the clk group, I have a patch based on Sascha's work. 
> > http://git.linaro.org/gitweb?p=people/riczhao/linux-2.6.git;a=shortlog;h=refs/heads/imx-clk
> 
> I thought further about this and a clock group is not something we want
> to have at all. Clocks are supposed to be arranged in a tree and
> grouping clocks together violates this which leads to problems.
> This grouping should be done at driver level, so when a driver needs
> more than one clock it should request them all, maybe with a clk_get_all
> helper function.
clock group is not limited to help driver get clock. It refects clock dependency.
For example, devices that possible access to on-chip RAM, depend on OCRAM clock. 
On imx53, VPU depends on OCRAM clock, even when VPU does not use OCRAM.

Thanks
Richard
> 
> Sascha
> 
> -- 
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