linux-kernel - Re: [PATCH v3 3/4] Documentation: devicetree: add PPMU events description

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Date:   Mon, 6 May 2019 12:29:38 +0200
From:   Lukasz Luba <l.luba@...tner.samsung.com>
To:     Rob Herring <robh@...nel.org>
Cc:     devicetree@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "open list:THERMAL" <linux-pm@...r.kernel.org>,
        linux-samsung-soc <linux-samsung-soc@...r.kernel.org>,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Chanwoo Choi <cw00.choi@...sung.com>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Sylwester Nawrocki <s.nawrocki@...sung.com>,
        MyungJoo Ham <myungjoo.ham@...sung.com>,
        Kukjin Kim <kgene@...nel.org>, willy.mh.wolff.ml@...il.com
Subject: Re: [PATCH v3 3/4] Documentation: devicetree: add PPMU events
 description

Hi Rob,

On 5/2/19 10:24 PM, Rob Herring wrote:
> On Thu, May 2, 2019 at 3:52 AM Lukasz Luba <l.luba@...tner.samsung.com> wrote:
>>
>> Hi Rob,
>>
>> On 5/1/19 12:36 AM, Rob Herring wrote:
>>> On Fri, Apr 19, 2019 at 03:48:07PM +0200, Lukasz Luba wrote:
>>>> Extend the documenation by events description with new 'event-data-type'
>>>> field. Add example how the event might be defined in DT.
>>>
>>> Why do we need event types in DT? We don't do this for other h/w such as
>>> ARM PMU.
>> In ARM PMU all the events are hard-coded into the driver code i.e. in v7
>> arch/arm/kernel/perf_event_v7.c
>> and are seen from perf. They are different type and for different
>> purpose. The Ecynos PPMU events are not seen in perf, they are
>> for internal monitoring and must not be reset by other actors like perf.
>> They are used by the 'bus drivers' to made some heuristics and tune the
>> internal settings, like frequency.
>>
>> Chanwoo has written PPMU driver which relies on DT definition.
>> The DT events are used by other DT devices by phandle.
> 
> How is that done? I don't see anything in the binding for that.
Here are the DT devices and how they are pinned together:
- declared devfreq events:
https://elixir.bootlin.com/linux/latest/source/arch/arm/boot/dts/exynos4412-ppmu-common.dtsi
- devfreq events pinned to the bus device:
https://elixir.bootlin.com/linux/latest/source/arch/arm/boot/dts/exynos4412-odroid-common.dtsi#L107
- the bus device itself:
https://elixir.bootlin.com/linux/latest/source/arch/arm/boot/dts/exynos4412.dtsi#L457

Regards,
Lukasz

> 
> Rob
> 
>