Re: Programming a clock in the device tree

[Peter Rosin <peda@lysator.liu.se>]

Hi!

On 2016-04-14 13:32, Sylwester Nawrocki wrote:
> On 04/14/2016 01:15 AM, Peter Rosin wrote:
>> Hi!
>>
>> I'm trying to connect (in a device tree) a programmable clock
>> to a device that does not expect the clock to need any
>> programming.
>>
>> I can hack this and add a clk_set_rate at the appropriate point
>> in the driver for the clk consumer, but I was expecting to see
>> some way of just adding a device tree node to get this done for
>> me.
>>
>> It just feels wrong to add this hack to the driver as the
>> programmable clock might be needed for more than one device and
>> the decisions by one driver might conflict with other needs (the
>> driver in question can use a variety of clock rates, so the rate
>> it should request is policy not belonging in a driver).
>>
>> Adding a device tree frequency property to the driver in question
>> is also a possibility, but that would need code duplication for
>> other clock consumers as well, when someone wants to use those
>> drivers in the way I'm now trying to use this driver.
>>
>> I.e. I expected to see a driver, just like the fixed clock
>> driver, but that programs a parent clock instead of just
>> representing a fixed oscillator. Is there such a thing? If not,
>> what is it that I'm not seeing? Because I just can't believe that
>> I'm the first person to need this...
> 
> How about using assigned-{clocks, clock-parents, clock-rates}
> properties in the clock provider node? Wouldn't it help in your
> case? Documentation can be found in Documentation/devicetree/
> bindings/clock/clock-bindings.txt

I added
	assigned-clocks = <&pck2>;
	assigned-clock-rates = <16000000>;
to the consumer node and that worked like a charm. That was exactly
what I was looking for, thanks!

Cheers,
Peter