Re: [PATCH V1 RESEND 1/3] perf/imx_ddr: Add system PMU identifier for userspace

[John Garry]

> > > > I also really dislike this. What's the preferred way to identify the 
> > > > SoC
> > > > from userspace?
> > >
> > > /proc/cpuinfo? ;)
> >
> > The *SoC*!
> >
> > > For an non-firmware specific case, I'd say soc_device should be. I'd
> > > guess ACPI systems don't use it and for them it's dmidecode typically.
> > > The other problem I have with soc_device is it is optional.
>
> Hi Will,
>
> > John -- what do you think about using soc_device to expose this 
> > information,
> > with ACPI systems using DMI data instead?
>
> Generally I don't think that DMI is reliable, and I saw this as the 
> least preferred choice. I'm looking at the sysfs DMI info for my dev 
> board, and I don't even see anything like a SoC identifier.
>
> As for the event_source device sysfs identifier file, it would not 
> always contain effectively the same as the SoC ID.
>
> Certain PMUs which I'm interested in plan to have probe-able 
> identification info available in future.

BTW, Shaokun now tells me that the HiSi uncore PMU HW have such 
registers to identify the implementation. I didn't know.

So we could add that identifier file for those PMUs as proof-of-concept, 
exposing that register.

As for other PMUs which I'm interested in, again, future versions should 
have such registers to self-identify.

So using something derived from the DT compat string would hopefully be 
the uncommon case.

Cheers,
John