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

[Rob Herring]

On Tue, May 7, 2019 at 4:05 AM Lukasz Luba <l.luba@xxxxxxxxxxxxxxxxxxx> wrote:
>
> Hi Rob,
>
> On 5/6/19 12:29 PM, Lukasz Luba wrote:
> > 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@xxxxxxxxxxxxxxxxxxx> 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
> >>
> >>
> Can I send the next version of the patch set, which has Chanwoo's
> suggestions, or do you have some objections to this PPMU entries?

I think the existing binding which this is based on needs some
changes, so it's pointless really for me to comment on additions.

Rob