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

[Lukasz Luba]

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
> 
>