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

[John Garry]

On 21/05/2020 14:04, Will Deacon wrote:
> On Wed, May 20, 2020 at 09:23:41AM -0600, Rob Herring wrote:
> > On Wed, May 20, 2020 at 1:33 AM Will Deacon <will@xxxxxxxxxx> wrote:
> > > On Tue, May 19, 2020 at 12:51:25PM -0600, Rob Herring wrote:
> > > > On Tue, May 12, 2020 at 03:31:13PM +0800, Joakim Zhang wrote:
> > > > > +static ssize_t ddr_perf_identifier_show(struct device *dev,
> > > > > +                                   struct device_attribute *attr,
> > > > > +                                   char *page)
> > > > > +{
> > > > > +   struct ddr_pmu *pmu = dev_get_drvdata(dev);
> > > > > +
> > > > > +   return sprintf(page, "%s\n", pmu->devtype_data->identifier);
> > > >
> > > > Why do we need yet another way to identify the SoC from userspace?
> > >
> > > 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.

Thanks,
John