linux-kernel - Re: [PATCH 3/5] ARM: berlin/dt: add cpupll and syspll support to BG2Q

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Date:	Fri, 21 Mar 2014 13:29:31 +0100
From:	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>
To:	Alexandre Belloni <alexandre.belloni@...e-electrons.com>
CC:	Mike Turquette <mturquette@...aro.org>, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	Antoine Ténart 
	<antoine.tenart@...e-electrons.com>
Subject: Re: [PATCH 3/5] ARM: berlin/dt: add cpupll and syspll support to
 BG2Q

On 03/21/2014 01:17 PM, Alexandre Belloni wrote:
> On 21/03/2014 at 13:11:29 +0100, Sebastian Hesselbarth wrote :
>> On 03/21/2014 12:43 PM, Alexandre Belloni wrote:
>>
>> Alexandre,
>>
>> Thanks for starting this! I'll start with the most obvious
>> things first and have a closer look on it later.
>>
>
> I will rework and wait for your other comments before sending a new
> version. BTW, I've set up a branch on github if you want to try on your
> platforms:
>
> https://github.com/alexandrebelloni/linux.git topic/berlin-clk
>
>> Missing commit description here.
>>
>>> Signed-off-by: Alexandre Belloni <alexandre.belloni@...e-electrons.com>
>>> ---
>>>   arch/arm/boot/dts/berlin2q.dtsi | 20 ++++++++++++++++++--
>>>   1 file changed, 18 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/arch/arm/boot/dts/berlin2q.dtsi b/arch/arm/boot/dts/berlin2q.dtsi
>>> index 07452a7483fa..19d2c82b0664 100644
>>> --- a/arch/arm/boot/dts/berlin2q.dtsi
>>> +++ b/arch/arm/boot/dts/berlin2q.dtsi
>>> @@ -59,10 +59,26 @@
>>>   		clock-frequency = <100000000>;
>>>   	};
>>>
>>> +	syspll: syspll {
>>
>> syspll: pll@...030 {
>>
>> and sort it in between other SoC nodes below. This will
>> most likely break clocks in v3.14 but v3.15 will receive
>> proper clock init ordering.
>>
>
> I will do across all the dtsi, don't bother repeating yourself :)
>
>>> +		compatible = "marvell,berlin2q-pll";
>>> +		clocks = <&smclk>;
>>> +		#clock-cells = <0>;
>>> +		reg = <0xf7ea0030 8>;
>>> +	};
>>> +
>>> +	cpupll: cpupll {
>>
>> dito.
>>
>>> +		compatible = "marvell,berlin2q-pll";
>>> +		clocks = <&smclk>;
>>> +		#clock-cells = <0>;
>>> +		reg = <0xf7dd0170 8>;
>>> +	};
>>> +
>>>   	cpuclk: cpu-clock {
>>> -		compatible = "fixed-clock";
>>> +		compatible = "fixed-factor-clock";
>>> +		clocks = <&cpupll>;
>>>   		#clock-cells = <0>;
>>> -		clock-frequency = <1200000000>;
>>> +		clock-div = <1>;
>>> +		clock-mult = <1>;
>>
>> Hmm, you probably know better than me, but if cpuclk == cpupll
>> is always true we don't need another clk layer here. If you
>> can scale down cpuclk from cpupll and we just have no driver
>> for it, I am fine with it.
>>
>
> You can actually switch CPU clk from CPU pll to smclk. I'm not sure this
> is completely useful yet though, probably for suspend ?

Then it should be clk mux instead?

> Also, while I'm not sure this is a good reason, other clocks are derived
> from CPU pll and have another divider.

I have no strong opinion, but a fixed-factor-clock with 1:1 just to
rename cpupll to cpuclk seems a bit wasty ;)

If there is a mux, we should add it now - no matter if we are ever
going to make any use of it. For the derived clocks we should be
careful if they actually depend on cpuclk or always cpupll.

If your (current) knowledge of the berlin clock trees is almost as
bad as mine, we can also ignore cpuclk mux if you prefer.

Sebastian
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