linux-kernel - Re: [PATCH 1/4] clk: samsung: out: Add infrastructure to register CLKOUT

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Date:	Thu, 15 May 2014 16:07:24 +0200
From:	Tomasz Figa <t.figa@...sung.com>
To:	Rahul Sharma <rahul.sharma@...sung.com>,
	Tushar Behera <tushar.behera@...aro.org>
Cc:	Pankaj Dubey <pankaj.dubey@...sung.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	linux-samsung-soc <linux-samsung-soc@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Mike Turquette <mturquette@...aro.org>,
	Kukjin Kim <kgene.kim@...sung.com>,
	Kumar Gala <galak@...eaurora.org>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Mark Rutland <mark.rutland@....com>,
	Pawel Moll <pawel.moll@....com>,
	Rob Herring <robh+dt@...nel.org>,
	sunil joshi <joshi@...sung.com>
Subject: Re: [PATCH 1/4] clk: samsung: out: Add infrastructure to register
 CLKOUT

Hi Rahul, Tushar,

On 15.05.2014 15:44, Rahul Sharma wrote:
> Hi Tushar,
> 
> Basically you are adding a new clock-type for Clkout. IMO clkout
> is not a special hardware. Existing clock types can be reused to
> support clkout. I see 3 major problem here:
> 
> 1) Clkout -> (Mux + Gate). You clubbed mux and gate together, and
> exposing as a single clock which is something like a composite clock.
> IMO this is not a recommended way in CCF.
> 
> 2) New Clock Type: Since clkout is just a combination of a simple
> mux and gate which are already supported, it is a unnecessary
> duplication.
> 
> 3) Clkout registered along with CMU: which is not correct. Clkout is in PMU
> (Separate physical IP) and should be registered as a independent Clock
> provider which provides 1 mux and 1 gate clock (As if now). It should also be
> well connected with main CMU.
> 
> I understand the challenge in using regmap interface for a clock provider. But
> we need to identify a clean solution. IMHO a independent clock provider with
> iomap, is relatively cleaner approach till CCF is not ready with regmap based
> reg access for clock registers.
> 
> Experts!! please comment.

It's quite unfortunate that Tushar has duplicated the effort to create a
clkout driver, considering the fact that we did have such driver
internally at SRPOL and it was quite nice and simple.

I will post a cleaned-up version today, that is about 2 times smaller in
terms of lines of added code and provides the same functionality,
without introducing custom clock types. In addition, it models the
clkout properly as a feature of PMU, not CMU (CMU only provides outputs
of particular sub-blocks that are fed into the PMU).

Best regards,
Tomasz
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