linux-kernel - Re: [RFC 1/1] clk: Add notifier support in clk_prepare_enable/clk_disable

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Date:	Fri, 15 Mar 2013 18:54:20 -0700
From:	Bill Huang <bilhuang@...dia.com>
To:	Stephen Warren <swarren@...dotorg.org>
CC:	Ulf Hansson <ulf.hansson@...aro.org>,
	Peter De Schrijver <pdeschrijver@...dia.com>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"patches@...aro.org" <patches@...aro.org>,
	"linaro-dev@...ts.linaro.org" <linaro-dev@...ts.linaro.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [RFC 1/1] clk: Add notifier support in
 clk_prepare_enable/clk_disable_unprepare

On Sat, 2013-03-16 at 03:38 +0800, Stephen Warren wrote:
> On 03/15/2013 06:33 AM, Ulf Hansson wrote:
> > On 15 March 2013 13:06, Bill Huang <bilhuang@...dia.com> wrote:
> >> On Fri, 2013-03-15 at 18:08 +0800, Ulf Hansson wrote:
> ...
> >>> Some prerequisites; I think am in favor of using the clk API to
> >>> trigger DVFS changes and then I agree on that clk_prepare|unprepare
> >>> needs to be possible to track from a DVFS perspective. clk_set_rate is
> >>> not enough.
> >>>
> >>> So if we decide to do the above (using the clk API to trigger DVFS
> >>> changes), I believe we should discuss two possible solutions;
> >>> - clk notifiers or..
> >>> - dvfs clock type.
> >>>
> >>> I am trying to make up my mind of what I think is the best solution.
> >>> Have you considered "dvfs clock type"?
> >>> I put some comments about this for "[PATCH 2/5] clk: notifier handler
> >>> for dynamic voltage scaling" recently as well.
> >>>
> >>> What could the advantages/disadvantages be between the two options?
> >>
> >> I personally prefer clk notifiers since that's easy and all the existing
> >> device drivers don't need to be modified, a new clock or API might be
> >> more thoroughly considered (and hence maybe more graceful) but that
> >> means we need more time to cook and many drivers need to plug into that
> >> API when it comes out, a lot of test/verification or maybe chaos
> >> follows, I'm not sure will that be a little overkill.
> > 
> > I guess you did not fully got what I meant with "dvfs clock type". It
> > will not affect the clock API. But instead the dvfs is handled by
> > implementing a specific clk hw type. So the same thing is accomplished
> > as with clk notifiers, no changes should be needed to device drivers.
> > 
> > The difference is only that no notifiers will be needed, and all the
> > dvfs stuff will be handled in the clk hw instead. It will mean that we
> > will bundle dvfs stuff into the clock drivers, instead of separating
> > the code outside the clock drivers. But, on the other hand no
> > notifiers will be needed.
> 
> The advantage here is that I assume that a notifier would continually
> have to check whether the clock being modified was one that the DVFS
> notifier cared about. By integrating the CVFS logic into the clk_hw

Actually, we can register notifier only on clocks that DVFS care about.


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