linux-kernel - Re: [PATCH 2/2] clk: Move init fields from clk to clk

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Date:	Tue, 20 Mar 2012 23:40:21 +0100
From:	Sascha Hauer <s.hauer@...gutronix.de>
To:	Saravana Kannan <skannan@...eaurora.org>
Cc:	Andrew Lunn <andrew@...n.ch>,
	Grant Likely <grant.likely@...retlab.ca>,
	Jamie Iles <jamie@...ieiles.com>,
	Jeremy Kerr <jeremy.kerr@...onical.com>,
	Mike Turquette <mturquette@...aro.org>,
	Magnus Damm <magnus.damm@...il.com>,
	Deepak Saxena <dsaxena@...aro.org>,
	linux-arm-kernel@...ts.infradead.org,
	Arnd Bergman <arnd.bergmann@...aro.org>,
	linux-arm-msm@...r.kernel.org,
	Rob Herring <rob.herring@...xeda.com>,
	Russell King <linux@....linux.org.uk>,
	Thomas Gleixner <tglx@...utronix.de>,
	Richard Zhao <richard.zhao@...aro.org>,
	Shawn Guo <shawn.guo@...escale.com>,
	Paul Walmsley <paul@...an.com>,
	Linus Walleij <linus.walleij@...ricsson.com>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Stephen Boyd <sboyd@...eaurora.org>,
	linux-kernel@...r.kernel.org,
	Amit Kucheria <amit.kucheria@...aro.org>,
	Shawn Guo <shawn.guo@...aro.org>
Subject: Re: [PATCH 2/2] clk: Move init fields from clk to clk_hw

On Tue, Mar 20, 2012 at 01:14:51PM -0700, Saravana Kannan wrote:
> On 03/20/2012 11:14 AM, Sascha Hauer wrote:
> >On Tue, Mar 20, 2012 at 03:17:10AM -0700, Saravana Kannan wrote:
> >>
> >>On Tue, March 20, 2012 2:40 am, Sascha Hauer wrote:
> >>>On Tue, Mar 20, 2012 at 12:54:55AM -0700, Saravana Kannan wrote:
> >>>>
> >>>I am using these functions and don't need a static array, I just call
> >>>the functions with the desired parameters.
> >>
> >>Sure, then let's leave it in. Curious, where do you get the desired
> >>parameters from? Is it static date in code or is it from DT? You somehow
> >>probe it?
> >
> >It's not from DT. See this thread:
> >
> >http://www.spinics.net/lists/arm-kernel/msg165839.html
> 
> Ah, I see. That's a lot of functions calls. I think it would be much
> more efficient if you just have an array and loop over it. With my
> patch, you can just call a single register function for all these
> clocks.

I was curious and gave it a try. I registered a fixed clock and 100
gates as child clocks. I tried both DEFINE_CLK_GATE and
clk_register_gate. It turned out there was no difference in speed.

> 
> >
> >The difference is that a struct clk_initializer is only used to
> >initialize a clock and not actively used by the clock framework. But as
> >you already mentioned using a copy inside the clock framework has the
> >same effect.
> 
> My opinion on this is to follow a wait and watch approach on the
> "flags" field. I really can't think of a safe way anyone can misuse
> it. If people start doing that, we can just do the copy and let them
> deal with their broken code. Until that happens, I don't want to
> waste time/space by copying it. The rest of the fields aren't
> actively used by the common clock code after init.

Actually you will save space by copying it because you can put the
initializers in __initdata and throw the initializers of unused SoCs
compiled into the kernel away during runtime.

Sascha

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