linux-kernel - Re: [PATCH v2 1/7] clk: Add a generic clock infrastructure

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Date:	Sun, 16 Oct 2011 19:55:21 +0200
From:	Sascha Hauer <s.hauer@...gutronix.de>
To:	Richard Zhao <richard.zhao@...aro.org>
Cc:	Mark Brown <broonie@...nsource.wolfsonmicro.com>, paul@...an.com,
	linaro-dev@...ts.linaro.org, linus.walleij@...ricsson.com,
	patches@...aro.org, shawn.guo@...escale.com, magnus.damm@...il.com,
	linux-kernel@...r.kernel.org, eric.miao@...aro.org,
	grant.likely@...retlab.ca, dsaxena@...aro.org,
	amit.kucheria@...aro.org, skannan@...cinc.com,
	linux@....linux.org.uk, jeremy.kerr@...onical.com,
	sboyd@...inc.com, Mike Turquette <mturquette@...com>,
	tglx@...utronix.de, linux-arm-kernel@...ts.infradead.org,
	arnd.bergmann@...aro.org
Subject: Re: [PATCH v2 1/7] clk: Add a generic clock infrastructure

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.

Sascha

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