Date:   Wed, 10 Jan 2018 20:54:12 -0600
From:   David Lechner <david@...hnology.com>
To:     Sekhar Nori <nsekhar@...com>, linux-clk@...r.kernel.org,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Cc:     Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...eaurora.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Kevin Hilman <khilman@...nel.org>,
        Adam Ford <aford173@...il.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 01/44] dt-bindings: clock: Add new bindings for TI
 Davinci PLL clocks

On 01/10/2018 12:52 PM, Sekhar Nori wrote:
> On Wednesday 10 January 2018 08:31 AM, David Lechner wrote:
>> On 01/09/2018 06:35 AM, Sekhar Nori wrote:
>>> On Monday 08 January 2018 09:59 PM, David Lechner wrote:
>>>> On 01/08/2018 08:00 AM, Sekhar Nori wrote:
>>>>> On Monday 08 January 2018 07:47 AM, David Lechner wrote:
> 
>>>>>> diff --git
>>>>>> a/Documentation/devicetree/bindings/clock/ti/davinci/pll.txt
>>>>>> b/Documentation/devicetree/bindings/clock/ti/davinci/pll.txt
>>>>>> new file mode 100644
>>>>>> index 0000000..99bf5da
>>>>>> --- /dev/null
>>>>>> +++ b/Documentation/devicetree/bindings/clock/ti/davinci/pll.txt
>>>>>> @@ -0,0 +1,47 @@
>>>>>> +Binding for TI DaVinci PLL Controllers
>>>>>> +
>>>>>> +The PLL provides clocks to most of the components on the SoC. In
>>>>>> addition
>>>>>> +to the PLL itself, this controller also contains bypasses, gates,
>>>>>> dividers,
>>>>>> +an multiplexers for various clock signals.
>>>>>> +
>>>>>> +Required properties:
>>>>>> +- compatible: shall be one of:
>>>>>> +    - "ti,da850-pll0" for PLL0 on DA850/OMAP-L138/AM18XX
>>>>>> +    - "ti,da850-pll1" for PLL1 on DA850/OMAP-L138/AM18XX
>>>>>
>>>>> These PLLs are same IP so they should use the same compatible. You can
>>>>> initialize both PLLs for DA850 based on the same compatible.
>>>>>
>>>>
>>>> But they are not exactly the same. For example, PLL0 has 7 PLLDIV clocks
>>>> while
>>>> PLL1 only has 3. PLL0 has PREDIV while PLL1 does not. PLL0 has certain
>>>> SYSCLKs
>>>> that are fixed-ratio but PLL1 does not have any of these. There are even
>>>> more
>>>> differences, but these are the ones we are actually using.
>>>
>>> We need each element of the PLLC to be modeled individually as a clock
>>> node.
>>
>> I gave this a good think while I have been working on this series
>> and I came to the conclusion that we really don't need to do this.
>> These components are all internal to the PLL IP block, so the
>> compatible string is enough to tell us what we have. They only
>> thing we need really in the device tree bindings are the connections
>> that are external to the IP block.
>>
>>
>>> That is, PLL should only model the multiplier, the dividers
>>> including post and prediv should be modeled as divider clocks (hopefully
>>> being able to use the clk-divider.c library). The sysclks can be
>>> fixed-factor-clock type clocks.
>>>
>>> Without this flexible mechanism, we cannot (at least later) model things
>>> like DIV4.5 clock which is the only clock which derives from the output
>>> of PLL multiplier before the post divider is applied.
>>>
>>> Since with DT there are are no retakes, we need to get this right the
>>> first time and modifying later will not be an option.
>>>
>>
>> So, the full device tree binding would look something like this:
>>
>> +
>> +    pll0: clock-controller@...00 {
>> +        compatible = "ti,da850-pll0";
>> +        reg = <0x11000 0x1000>;
>> +        clocks = <&ref_clk>, <&pll1_sysclk 3>, <&pll1_obsclk>;
>> +        clock-names = "oscin", pll1_sysclk3", "pll1_osbclk";
>> +        oscin-square-wave;
>> +
>> +        pll0_sysclk: sysclk {
>> +            #clock-cells = <1>;
>> +        };
>> +
>> +        pll0_auxclk: auxclk {
>> +            #clock-cells = <0>;
>> +        };
>> +
>> +        pll0_div45: div4.5 {
>> +            #clock-cells = <0>;
>> +        };
>> +
>> +        pll0_obsclk: obsclk {
>> +            #clock-cells = <0>;
>> +            assigned-clocks = <&pll0_sysclk 1>;
>> +            assigned-clock-names = "ocsrc";
>> +        };
>> +    };
> 
> Well, I guess this will work as well. And I am probably biased towards
> the style I mentioned because AM335x and other TI OMAP processors
> follow that.
> 
> To make it easy to review that we have all bases covered, can you model
> the all PLLC0 and PLLC1 (input and output) clocks for the next version?

Sure thing.

> 
>>
>> There are three clocks coming into the IP block and there are 11 clocks
>> going out (sysclk is 7 clocks). And you can specify the board-specific
>> configuration, like having the "oscin-square-wave" flag when a square wave
>> is used instead of a crystal oscillator and you can assign the multiplexer
> 
> Ideally the OSCIN vs CLKIN selection should be another clock mux whose
> output is one of the input clocks to PLL controller. But I can see the
> difficulty in handling that as the mux itself is controlled by the PLL
> controller.
> 
>> input that will be used by obsclk. (And, this binding is totally compatible
>> with the binding I have already proposed - although, I see now it would
>> be better to go ahead and add the clocks-names property.)
> 
> Also, please add the oscin-square-wave to the binding definition too.
> 
> For the benefit of others reviewing and not familiar with the hardware,
> the users guide for DA850 is here:
> http://www.ti.com/lit/ug/spruh77c/spruh77c.pdf
> 
> and the PLL block diagram is on page 143 (Figure 8-1).
> 
> Thanks,
> Sekhar
> 

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