Re: Virtual devices (cpufreq etc) and DT

[Rob Herring <robherring2-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

On 08/03/2011 11:41 AM, Jamie Iles wrote:
> On Wed, Aug 03, 2011 at 11:29:16AM -0500, Rob Herring wrote:
>> On 08/03/2011 04:50 AM, Jamie Iles wrote:
>>> 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?
> 
I'm separating it out for mine and just doing limited clk implementation
now based on the rate common struct clk is going.

There's a 3rd option. Implement DT clk binding parsing and clk node
creation within your platform. Perhaps the struct clk details could be
abstracted out from the binding parsing code so some could still be common.

Rob

>>>
>>> 	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!
> 
>>> 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