Re: Virtual devices (cpufreq etc) and DT

On Wed, Aug 03, 2011 at 11:29:16AM -0500, Rob Herring wrote:

On 08/03/2011 04:50 AM, Jamie Iles wrote:

quoted

I'm trying to work out how our cpufreq driver fits in with device tree 
bindings.  We have a simple driver that just takes a struct clk and 
calls clk_set_rate() on it.  Is a node in the device tree the right way 
to do this as it isn't really a physical device?  I have the PLL in the 
clocks group of the DT:

Sounds generically useful...

Yes, once I've got it working internally I'll submit this as a generic 
thing for drivers/cpufreq.

The OF clock bindings are not really completely finalized and work on
the OF clk code is basically blocked waiting on the common struct clk
infrastructure.

OK, so for the platform I'm working on mainlining at the moment does 
that mean I should leave the clock bindings for now or is that something 
that can be revised at a later date?

quoted

	clocks {
		...

		arm_clk: clock@11 {
			compatible = "picochip,pc3x3-pll";
			reg = <0x800a0050 0x8>;
			picoxcell,min-freq = <140000000>;
			picoxcell,max-freq = <700000000>;
			ref-clock = <&ref_clk>, "ref";
			clock-outputs = "cpu";
		};
	};

This describes the clock output. You still need to describe the
connection which is what the cpufreq driver should get. For that you
need something like this:

	cpu@0 {
		compatible = "arm,cortex-a9";
		reg = <0>;
		cpu-clock = <&arm_clk>, "cpu";
	};

	cpu@1 {
		compatible = "arm,cortex-a9";
		cpu-clock = <&arm_clk>, "cpu";
	};

Then look for the cpu node(s) and get it's clock.

Ahh, I hadn't thought of adding it to the cpu node, that's a nice way of 
representing it!

quoted

so I could reference that.  The of clk interface also requires a struct 
device for getting the clk so I guess this is needed...

I ran into that problem as well. Making of_clk_get take a struct
device_node ptr instead of struct device fixes the problem. Here's a
patch that does that.

Nice, thanks Rob!

Jamie