linux-kernel - Re: [RFC] Common clock framework for external clock generators

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Message-ID: <507A9E72.2030800@gmail.com>
Date:	Sun, 14 Oct 2012 13:13:54 +0200
From:	Daniel Mack <zonque@...il.com>
To:	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>
CC:	linux-kernel@...r.kernel.org,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Mike Turquette <mturquette@...com>,
	linux ARM <linux-arm-kernel@...ts.infradead.org>,
	Grant Likely <grant.likely@...retlab.ca>,
	Rob Herring <rob.herring@...xeda.com>,
	devicetree-discuss@...ts.ozlabs.org
Subject: Re: [RFC] Common clock framework for external clock generators

Hi,

On 14.10.2012 12:59, Sebastian Hesselbarth wrote:
> Adding LAKML and devtree as there might be people willing to comment about
> DT representation of i2c-attached clock generators, too.
> 
> On 10/12/2012 08:17 PM, Daniel Mack wrote:
>> On 11.10.2012 18:00, Sebastian Hesselbarth wrote:
>  >> [...]
>>> Does any of you work rely on a working si5351 driver?
>>
>> Yes, it does actually. I can hack around it for now, but at some point,
>> a proper driver is needed. And yours looks quite feature complete, so it
>> would be easiest to finish this one :)
> 
> Well, yes it is some kind of feature complete except regmap and DT. Adding
> regmap to the driver should be quite easy but with DT I am still thinking
> of the best way to represent the internal connections between OSC, PLLs, and
> CLKOUTs. In the last version of the driver I had a callback that was
> board specific to setup these connections but with DT there will be no board
> specific code anymore.
> 
> Maybe one of the common clk maintainers can give a hint how this could be
> done in a clean way. The question is how to represent a i2c-attached clock
> generator config in DT where you want to setup clock parents of CLKOUTs and
> PLLs.
> 
> A possible solution would be something like this:
> 
> si5351a@60 {
> 	compatible = "silabs,si5351a";
> 	reg = <0x60>;
> 
> 	si_osc: osc {
> 		compatible = "fixed-clock";
> 		clock-frequency = <270000000>;
> 	};
> 
> 	si_plla: pll@0 {
> 		compatible = "silabs,si5351-pll";
> 		/* hook-up plla to osc input */
> 		clocks = <&si_osc>;
> 	};
> 
> 	si_clkout0: clkout@0 {
> 		compatible = "silabs,si5351-clkout";
> 		/* hook-up clkout0 to plla */
> 		clocks = <&si_plla>;
> 		/* request target frequency */
> 		clock-frequency = <148500000>;
> 	};	
> };
> 
> Although this perfectly describes the clock hierarchy I still don't like
> the sub-node style. Another flat solution would be something like:

I think the sub-node style above it nicer because it allows referencing
the individual clocks outputs with a phandle. We use this chip to
generate base-frequencies for audio clocks, and so we have to switch
between two freqs for the multiples of 22.5KHz and 24KHz at runtime.

>> Do you still have access to hardware you wrote the driver for? Let me
>> know if you need any help around here.
> 
> Yes, hardware is still available although I only have access to the Si5351a
> with 3 clkouts. The code should be compatible for Si5351a with 8 clkouts and
> code skeleton for 5351b (OSC and VXCO input) and 5351c (OSC and CLKIN) is
> there but untested.

The 3 clkout model is the only one I have access to as well.

> I've transferred the current driver version to my repository to work on. As soon
> as I have regmap done, I will push it online and give you a note.

That's great. Let me know if you want me to test anything.


Thanks,
Daniel


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