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

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Date:   Thu, 2 May 2019 15:24:20 -0500
From:   Rob Herring <robh@...nel.org>
To:     Lukasz Luba <l.luba@...tner.samsung.com>
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

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.

Rob