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

From: Rob Herring
Date: Thu May 02 2019 - 16:24:58 EST

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.