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

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Date:	Mon, 17 Oct 2011 13:05:39 +0200
From:	Sascha Hauer <s.hauer@...gutronix.de>
To:	Richard Zhao <richard.zhao@...aro.org>
Cc:	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	jeremy.kerr@...onical.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, arnd.bergmann@...aro.org, sboyd@...inc.com,
	tglx@...utronix.de, linux-arm-kernel@...ts.infradead.org,
	Mike Turquette <mturquette@...com>
Subject: Re: [PATCH v2 1/7] clk: Add a generic clock infrastructure

On Mon, Oct 17, 2011 at 06:53:03PM +0800, Richard Zhao wrote:
> On Mon, Oct 17, 2011 at 10:20:28AM +0100, Mark Brown wrote:
> > On Mon, Oct 17, 2011 at 04:48:52PM +0800, Richard Zhao wrote:
> > 
> > > For example, devices that possible access to on-chip RAM, depend on OCRAM clock. 
> > > On imx53, VPU depends on OCRAM clock, even when VPU does not use OCRAM.
> > 
> > So if the VPU depends on OCRAM the VPU should be enabling the OCRAM
> > clock.  The function of a given clock isn't terribly relevant, and
> > certainly grouping clocks together doesn't seem to be the obvious
> > solution from what you've said
> VPU don't know OCRAM clk, it's SoC specific. I know it's clock function
> replationship. But it's the only better place to refect the dependency 
> in clock tree. Another dependency example, from SoC bus topology, some bus
> clk always depends on bus switch/hub.
> > - if the driver doesn't know about the
> > clock it seems like the core ought to be enabling it transparently
> > rather than gluing it together with some other random clock.
> If you mean clk core here, then we need things like below:
> struct clk_hw {
> 	struct clk *clk;
> 	struct dependency {
> 		struct clk_hw *clks;
> 		int count;
> 	};
> };
> Though Mike does not like to add things in clk_hw, but it's the only place
> to put common things of clk drivers.

It's not a problem to associate multiple clocks to a device, we can do
this now already. What a driver can't do now is give-me-all-clocks-I-need(dev),
but this problem should not be solved at clock core level but at the
clkdev level.
The fact is that the different clocks for a device are really different
clocks. A dumb driver may want to request/enable all relevant clocks at
once while a more sophisticated driver may want to enable the clock for
accessing registers in the probe function and a baud clock on device
open time.

Sascha

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