linux-kernel - Re: [PATCH v5 3/4] clk: introduce the common clock framework

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Date:	Mon, 19 Mar 2012 12:22:52 +0100
From:	Sascha Hauer <s.hauer@...gutronix.de>
To:	Shawn Guo <shawn.guo@...aro.org>
Cc:	"Turquette, Mike" <mturquette@...com>,
	Andrew Lunn <andrew@...n.ch>, Paul Walmsley <paul@...an.com>,
	linaro-dev@...ts.linaro.org,
	Linus Walleij <linus.walleij@...ricsson.com>,
	patches@...aro.org, Stephen Boyd <sboyd@...eaurora.org>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Magnus Damm <magnus.damm@...il.com>,
	linux-kernel@...r.kernel.org,
	Rob Herring <rob.herring@...xeda.com>,
	Richard Zhao <richard.zhao@...aro.org>,
	Grant Likely <grant.likely@...retlab.ca>,
	Deepak Saxena <dsaxena@...aro.org>,
	Saravana Kannan <skannan@...eaurora.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Shawn Guo <shawn.guo@...escale.com>,
	Amit Kucheria <amit.kucheria@...aro.org>,
	Russell King <linux@....linux.org.uk>,
	Jeremy Kerr <jeremy.kerr@...onical.com>,
	Arnd Bergman <arnd.bergmann@...aro.org>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v5 3/4] clk: introduce the common clock framework

On Mon, Mar 19, 2012 at 03:01:17PM +0800, Shawn Guo wrote:
> On Fri, Mar 09, 2012 at 10:25:00AM -0800, Turquette, Mike wrote:
> ...
> > However if you have the ability to use the clk_foo_register functions
> > please do use them in place of static initialization.  The static init
> > stuff is only for folks backed into a corner and forced to use it...
> > for now.  I'm looking at ways to allow for kmalloc'ing in early boot,
> > as well as reducing the number of clocks that my platform registers
> > during early boot drastically.
> > 
> While I agree using registration functions rather than static
> initialization will help make "struct clk" an opaque cookie, I also
> see some benefit with using static initialization over registration
> functions.  That is we will be able to initialize parents statically
> rather than calling expensive __clk_lookup() to find them when using
> registration functions.
> 
> I'm not sure if this will be a concern with the platforms that have
> hundreds of clocks.  Keep it in mind, when we say one clock, there
> are generally 3 clks behind it, clk_gate, clk_divider and clk_mux.

On an i.MX51 with a fully dynamically allocated clock tree it takes
about 10ms to initialize the tree which I think is acceptable. The
clock tree is not complete, but I would think that about 70% of the
clocks are there.
Normally less performant platforms will have less clocks, so I assume
the times will be comparable.

Sascha

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