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Subject: Re: [PATCH v2 00/11] thermal: add new flag irq-mode for trip point
To:     Zhang Rui <rui.zhang@intel.com>, devicetree@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org,
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        mark.rutland@arm.com, corbet@lwn.net, b.zolnierkie@samsung.com,
        krzk@kernel.org
From:   Lukasz Luba <l.luba@partner.samsung.com>
Message-ID: <ffca9e30-7a7c-7f61-24a1-016c9ea1e611@partner.samsung.com>
Date:   Wed, 5 Dec 2018 16:33:37 +0100
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Hi Rui,

On 12/5/18 4:08 PM, Zhang Rui wrote:
> On 三, 2018-11-07 at 18:09 +0100, Lukasz Luba wrote:
>> Hi all,
>>
>> This patch set adds a new flag and mechanism in thermal trip points
>> in
>> DT.  The old implementation in thermal zone in DT sets the same
>> configuration for all internal trip points. It does not work for all
>> HW.  There are SoCs which support IRQs for some trip points (i.e.
>> Exynos 4 has 4 trip points with IRQs). For additional one defined
>> inside the thermal zone there is a need of 'polling'. When developer
>> adds polling mode settings inside the thermal zone, all the trip
>> points will be registered for polling, even those supporting IRQs,
>> which does not make sense.
> 
> we have two timers, one for polling, and one for passive cooling.
> I think we are talking about passive cooling timer only, right?
> And the real problem is that we have multiple passive trip points and
> only part of them support irq_mode, and we don't want to start the
> passive polling timer for all of the passive trip points.
Yes exactly, we don't want to poll all of them by starting 'passive 
polling timer'.

Regards,
Lukasz
> 
> thanks,
> rui
> 
>>   Thus, developers create workarounds, which
>> are confusing for some other developers.  To workaround,
>> people declare some trip points as 'active' (those with IRQ support).
>> It allows to bypass polling mode in thermal framework applied for
>> all thermal zone's trip points.
>>
>> Thermal framework defines 4 types of trip points. The 'passive' means
>> passive cooling using DVFS, 'active' is designed for fan and other
>> devices actively changing the outside conditions. Therefore, a
>> workaround
>> mentioned earlier is confusing when someone does not know about the
>> framework limitations.
>>
>> This patch set tries to solve the issue by adding one flag inside the
>> trip point: 'irq-mode;'.  The trip point 'passive' declared in DT
>> with
>> explicit flag 'irq-mode;' will not register itself as polling mode.
>> Thermal framework will skip it during scheduling next read out work.
>> The old global-polling-mode-configuration-inside-thermal-zone is
>> still
>> valid.  Patch set does not break existing design for trip points
>> which
>> do not have 'irq-mode' flag - they will use polling.
>>
>> As an example please check patch #10 for Exynos4 SoC family, where
>> there
>> is 4 HW supported trip points and there is a need of 6. The rest 2
>> are
>> declared as 'passive' without 'irq-mode;' flag, which means polling
>> mode needed for them.
>>
>> Patch #1 is a small cleanup in thermal framework.
>>
>> Change log:
>> v2
>> - changed description in cover letter
>> - change commit messages according to Krzysztof comments
>> - rebase on top of current mainline (v4.20-rc1)
>>
>> Regards,
>> Lukasz Luba
>>
>> Lukasz Luba (11):
>>    thermal: remove unused function parameter
>>    thermal: add irq-mode configuration for trip point
>>    thermal: add new sysfs file for irq-mode
>>    Doc: thermal: new irq-mode for trip point
>>    Doc: DT: thermal: new irq-mode for trip point
>>    arm64: dts: exynos5433: add support for thermal trip irq-mode
>>    arm64: dts: exynos7: add support for thermal trip irq-mode
>>    arm: dts: exynos4: add support for thermal trip irq-mode
>>    arm: dts: exynos5420: add support for thermal trip irq-mode
>>    arm: dts: exynos5422: add support for thermal trip irq-mode
>>    arm: dts: exynos5410: add support for thermal trip irq-mode
>>
>>   .../devicetree/bindings/thermal/thermal.txt        |   7 ++
>>   Documentation/thermal/sysfs-api.txt                |   9 ++
>>   arch/arm/boot/dts/exynos4-cpu-thermal.dtsi         |  10 +-
>>   arch/arm/boot/dts/exynos5410-odroidxu.dts          |  10 +-
>>   arch/arm/boot/dts/exynos5420-trip-points.dtsi      |  10 +-
>>   arch/arm/boot/dts/exynos5422-odroidxu3-common.dtsi |  40 +++++---
>>   arch/arm64/boot/dts/exynos/exynos5433-tmu.dtsi     | 105
>> ++++++++++++++-------
>>   .../arm64/boot/dts/exynos/exynos7-trip-points.dtsi |   8 ++
>>   drivers/thermal/of-thermal.c                       |  17 ++++
>>   drivers/thermal/thermal_core.c                     |  16 ++--
>>   drivers/thermal/thermal_sysfs.c                    |  53 ++++++++++-
>>   include/linux/thermal.h                            |   5 +
>>   12 files changed, 226 insertions(+), 64 deletions(-)
>>
> 
>