Re: [PATCH V2 1/3] ARM: dts: tegra: add clock source for PMC

[Stephen Warren <swarren-3lzwWm7+Weoh9ZMKESR00Q@public.gmane.org>]

On 03/20/2013 04:12 AM, Joseph Lo wrote:
> On Wed, 2013-03-20 at 00:42 +0800, Stephen Warren wrote:
>> On 03/18/2013 02:09 AM, Joseph Lo wrote:
>>> The clock source of PMC is PCLK. Adding it into DTS for Tegra20 and Tegra30.
>>
>>> diff --git a/arch/arm/boot/dts/tegra20.dtsi b/arch/arm/boot/dts/tegra20.dtsi
>>
>>>  	pmc {
>>>  		compatible = "nvidia,tegra20-pmc";
>>>  		reg = <0x7000e400 0x400>;
>>> +		clocks = <&tegra_car 110>;
>>>  	};
>>
>> The DT binding documentation needs to list the set of clocks that must
>> be present.
>>
>> Doesn't the PMC also receive a "clk32k_in" from the PMIC, or is that
>> routed into the CAR, and then into the PMC? Either way, the PMC module
>> receives that clock somehow. Since there are multiple clocks, that also
>> means that a clock-names property is required.
> 
> Do you mean the DTS below and add it into binding document?
> 
> / SoC dts including file
> pmc {
> 	compatible = "nvidia,tegra20-pmc";
> 	reg = <0x7000e400 0x400>;
> 	clocks = <&tegra_car 110>, <&clk32k_in>;
> 	clock-names= "pclk", "clk32k_in";
> };

Yes, that's what should technically be present.

> / Tegra board dts file
> 
> pmic {
> 	...
> 	clocks {
> 		compatible = "simple-bus";
> 		#address-cells = <1>;
> 		#size-cells = <0>;
> 
> 		clk32k_in: clock@0 {
> 			compatible = "fixed-clock";
> 			reg=<0>;
> 			#clock-cells = <0>;
> 			clock-frequency = <32768>;
> 		};
> 	};
> };

That won't work; the PMIC drivers don't enumerate sub-nodes as busss, so
 that clocks node won't ever be processed. Also, the PMIC drivers aren't
clock providers in most cases. It's not quite a correct representation
of the HW, but I would suggest simply creating a top-level "clock" node
for that fixed clock. If we ever have more top-level clocks, we can move
them into a top-level "clocks" node at that time.

Note: If there aren't already any other top-level clock nodes (which I
think is the case), the node can be named just "clock" rather than
"clock@0", since there are no naming conflicts.