linux-kernel - Re: [PATCH 1/5] thermal: exynos: enable core tmu clk on exynos platform

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Date:   Wed, 18 Jul 2018 12:06:55 +0200
From:   Krzysztof Kozlowski <krzk@...nel.org>
To:     Anand Moon <linux.amoon@...il.com>
Cc:     Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Zhang Rui <rui.zhang@...el.com>,
        Eduardo Valentin <edubezval@...il.com>,
        Kukjin Kim <kgene@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Linux PM list <linux-pm@...r.kernel.org>,
        "linux-samsung-soc@...r.kernel.org" 
        <linux-samsung-soc@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel <linux-kernel@...r.kernel.org>,
        devicetree <devicetree@...r.kernel.org>
Subject: Re: [PATCH 1/5] thermal: exynos: enable core tmu clk on exynos platform

On 18 July 2018 at 11:24, Anand Moon <linux.amoon@...il.com> wrote:
> Hi Krzysztof
>
> On 18 July 2018 at 11:47, Krzysztof Kozlowski <krzk@...nel.org> wrote:
>> On 17 July 2018 at 22:23, Anand Moon <linux.amoon@...il.com> wrote:
>>> Hi Krzysztof
>>>
>>> On 17 July 2018 at 17:50, Krzysztof Kozlowski <krzk@...nel.org> wrote:
>>>> Hi Anand,
>>>>
>>>> Thanks for patch.
>>>>
>>>> On 17 July 2018 at 12:12, Anand Moon <linux.amoon@...il.com> wrote:
>>>>> clk_summary do not show tmu_apbif clk enable, so replace
>>>>> the clk_prepare with clk_prepare_enables to enable tmu clk.
>>>>
>>>> This is not valid reason to do a change. What is clk_summary does not
>>>> really matter. Your change has negative impact on power consumption as
>>>> the clock stays enabled all the time. This is not what we want... so
>>>> please explain it more - why you need the clock to be enabled all the
>>>> time? What is broken (clk_summary is not broken in this case)?
>>>>
>>>
>>> Opps I could not explain some more in my commit message.
>>>
>>> Actually TMU sensor for Exynos process are controlled by so external clk
>>>
>>> Exynos4412 have VDD18_TS sensor which controls the CLK_SENSE tmu.
>>> Exynos5422 have VDD18_TS01 / VDD18_TS23 / VDD18_TS4 sensor which
>>> control the CLK_SENSE tmu.
>>>
>>> So as per my understanding tmu is clk driver which control the flow  PMIC.
>>>
>>> clk_prepare_enable combine clk_prepare and clk_enable
>>> and clk_disable_unprepare combine clk_disable and clk_unprepare.
>>>
>>> most of the driver prefer clk_prepare_enable and clk_disable_unprepare.
>>>
>>> clk_summary is just a reference looking point where we could check the
>>> clk is enable/disable.
>>>
>>> what is broken ?
>>> I still few more parameter need to tuned to configure the tmu driver.
>>
>> I am sorry but I am still unable to see what is broken and what are
>> you trying to fix. I asked what is broken and you replied that there
>> is a sensor, there is a clock, drivers use clk_prepare_enable and some
>> more parameter need to be tuned... None of these are answers to
>> question - what is broken. How can I reproduce the problem?
>>
>> Best regards,
>> Krzysztof
>
> Basically I use thermal testing.
>
> # git clone https://git.linaro.org/power/pm-qa.git
> # cd pm-qa
> # make -C thermal check
>
> most of the testcase failed on Exynos5422 but some pass on Exynos4412.
>
> Attach is the software overview from Exynos5422 user manual.
>
> I am not able to explain in deep technically, but I have studied other thermal
> driver to draw into conclusion that tmu clk's need to be enabled.

That is true in general - the clk has to be enabled in certain cases.
However you did not say at all when you want this clock to be
enabled... and the your patch enables it for entire lifetime of
device.

> If you feel the we should not enable these clk, them I will drop the
> clk_prepare_enable check
> and resubmit the changes with better commit message.

I don't know. This was fifth email in this thread and it is the first
time some real problem is mentioned. Still the issue is not described
entirely so I really do not have a clue whether this patch fixes
something or not.
What is more, you mentioned falling pm-qa tests here (not in commit
msg) but did not say whether this patch fixes anything or not.

So let me summarize it:
1. You did not describe the problem you want to fix.
2. The patch looks incorrect because it enables the clock for entire
lifetime of device which we do not want.
3. The patch might or not might fix some problem. We even do not know what...
4. The clock not being enabled when not needed... is obviously not a problem.

Please start from beginning. Find the problem, tell us how it can be
reproduced and deliver a single patch which fixes the problem.

This pattern of your code - fixing something without describing the
problem - happened many time before. I repeated this some times before
as well. I would prefer not to repeat to many times. Therefore I would
be happy if you follow the path mentioned in paragraph before always:
find the problem, tell how it can be reproduced, deliver single patch
which fixes the problem.

Best regards,
Krzysztof