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

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Message-ID: <20200521130415.GB5949@willie-the-truck>
Date:   Thu, 21 May 2020 14:04:16 +0100
From:   Will Deacon <will@...nel.org>
To:     Rob Herring <robh@...nel.org>
Cc:     Joakim Zhang <qiangqing.zhang@....com>,
        John Garry <john.garry@...wei.com>,
        Mark Rutland <mark.rutland@....com>,
        Shawn Guo <shawnguo@...nel.org>,
        NXP Linux Team <linux-imx@....com>,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>, devicetree@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V1 RESEND 1/3] perf/imx_ddr: Add system PMU identifier
 for userspace

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@...nel.org> 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.

John -- what do you think about using soc_device to expose this information,
with ACPI systems using DMI data instead?

Will