Date:   Wed, 17 Jul 2019 14:55:53 +0200
From:   Lukasz Luba <l.luba@...tner.samsung.com>
To:     Krzysztof Kozlowski <krzk@...nel.org>
Cc:     devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        "linux-samsung-soc@...r.kernel.org" 
        <linux-samsung-soc@...r.kernel.org>, linux-clk@...r.kernel.org,
        mturquette@...libre.com, sboyd@...nel.org,
        Bartłomiej Żołnierkiewicz 
        <b.zolnierkie@...sung.com>, kgene@...nel.org, mark.rutland@....com,
        robh+dt@...nel.org, Chanwoo Choi <cw00.choi@...sung.com>,
        kyungmin.park@...sung.com, Andrzej Hajda <a.hajda@...sung.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        s.nawrocki@...sung.com, myungjoo.ham@...sung.com
Subject: Re: [PATCH v1 37/50] ARM: dts: exynos: change parent and rate of
 bus_fsys in Exynos5422


On 7/17/19 1:11 PM, Krzysztof Kozlowski wrote:
> On Wed, 17 Jul 2019 at 13:06, Lukasz Luba <l.luba@...tner.samsung.com> wrote:
>>
>>
>>
>> On 7/17/19 12:45 PM, Krzysztof Kozlowski wrote:
>>> On Wed, 17 Jul 2019 at 12:39, Lukasz Luba <l.luba@...tner.samsung.com> wrote:
>>>>>>
>>>>>>     &bus_fsys {
>>>>>>            devfreq = <&bus_wcore>;
>>>>>> +       assigned-clocks = <&clock CLK_MOUT_ACLK200_FSYS>,
>>>>>> +                         <&clock CLK_DOUT_ACLK200_FSYS>,
>>>>>> +                         <&clock CLK_FOUT_DPLL>;
>>>>>> +       assigned-clock-parents = <&clock CLK_MOUT_SCLK_DPLL>;
>>>>>> +       assigned-clock-rates = <0>, <240000000>,<1200000000>;
>>>>>
>>>>> Here and in all other patches:
>>>>> I am not entirely sure that this should be here. It looks like
>>>>> property of the SoC. Do we expect that buses will be configured to
>>>>> different clock rates between different boards?
This is the board file for Exynos5420/5422/5800 which enables buses.
Thus, I have change them here. Patch 49/50 adds these buses to
Exynos5800 (Peach Pi). In Exynos5420 there is no clock tree for
bus_isp266. The parents for different devices could be also different.
It is because i.e. in 5420 there is 2 bit in the WCORE 1st mux while in
5422 there is 3 bits (6 parents possible).
That's why I have picked exynos5422-odroid-core.dtsi to reference
the bus devices and pinned them into proper parent and changed rate.
When you check patch 49/50 for 5800 not all the parents are the same.

(1) I could create a dedicated files like: exynos5422-bus.dtsi,
exynos5420-bus.dtsi, exynos5800-bus.dtsi which would include some
base file with the basic &bus_X and set the right parent, rate.
Then these files would be included into proper board file like:
exynos5800-peach-pi.dts.
Is this something that you would like to see?
  Since the OPP tables
>>>>> are shared (they are property of the SoC, not board) then I would
>>>>> assume that default frequency is shared as well.
>>>> These clocks they all relay on some bootloader configuration. It depends
>>>> which version of the bootloader you have, then you might get different
>>>> default configuration in the clocks.
>>>
>>> I do not agree here. This configuration is not dependent on
>>> bootloader. Although one bootloader might set the clocks to X and
>>> other to Y, but still you provide here valid configuration setting
>>> them, e.g. to Y (or to Z). What bootloader set before does not matter
>>> because you always override it.
>> This exactly the patch set is aim to do: overwrite any bootloader
>> configuration which could be wrong set after boot.
>> I don't know for how long it is left in such
>> 'bootloader-default-clock-settings' but it is not accurate
>> configuration. The pattern in the DT to change the clock rates is
>> there.
> 
> Still it is not the answer to my concerns and questions.
Please look at my answer above.
> 
>>>
>>>> The pattern of changing the parent
>>>> or even rate is known in the DT files (or I am missing something).
>>>> When you grep for it, you get 168 hits (38 for exynos*):
>>>> git grep -n "assigned-clock-rates" ./arch/arm/boot/dts/ | wc -l
>>>
>>> Yeah, and if you grep per type you got:
>>> DTSI: 114
>>> DTS: 54
>>> so what do you want to say?
>> Thus, It could be changed in DT.
> 
> Of course, why not. But how this relevant to my question?
Please see above.
> 
>>> My thinking is that all the boards have buses configured to the same
>>> initial frequency. I am not questioning the use of
>>> assigned-clock-rates at all. Just the place...
>> It is not only 'initial frequency' as you name it. It has three changes:
>> - re-parent to proper PLL
>> - changing this PLL rate
>> - change the OPPs frequency values to integer values derived from PLL
>>
>> The initial frequencies will be changed by devfreq governor using OPP
>> tables and the load after the whole system boots.
> 
> I simplified with "initial frequency" but it does not matter. Let me
> try to raise my concerns again, different wording:
> All this looks like property of the SoC, not the board, because:
> 1. the OPPs are already properties of the SoC, not the board (XU3 Lite
> is kind of exception but in fact it uses different flavor of
> Exynos5422 SoC which we do not model here as separate DTSI),
Please see above at (1).
> 2. I expect all boards to have the same properties.
All boards which have the same SoC, i.e. Exysno5422 <- then I agree.

Thank you for the comments.

Regards,
Lukasz
> 
> Best regards,
> Krzysztof
> 
> 

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