linux-kernel - Re: [External] Re: [PATCH] perf/dwc_pcie: fix duplicate pci

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Message-ID: <20250127165156.GE25757@willie-the-truck>
Date: Mon, 27 Jan 2025 16:51:57 +0000
From: Will Deacon <will@...nel.org>
To: yunhui cui <cuiyunhui@...edance.com>
Cc: Shuai Xue <xueshuai@...ux.alibaba.com>, renyu.zj@...ux.alibaba.com,
	mark.rutland@....com, linux-arm-kernel@...ts.infradead.org,
	linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [External] Re: [PATCH] perf/dwc_pcie: fix duplicate pci_dev
 devices

On Sun, Jan 26, 2025 at 09:54:35AM +0800, yunhui cui wrote:
> Hi Will,
> 
> On Fri, Jan 24, 2025 at 8:30 PM Will Deacon <will@...nel.org> wrote:
> >
> > On Fri, Jan 24, 2025 at 05:11:05PM +0800, yunhui cui wrote:
> > > > >>>        vsec = dwc_pcie_des_cap(pdev);
> > > > >>>        if (!vsec)
> > > > >>>                return -ENODEV;
> > > > >>>
> > > > >>>        sbdf = plat_dev->id;
> > > > >>> -     name = devm_kasprintf(&plat_dev->dev, GFP_KERNEL, "dwc_rootport_%x", sbdf);
> > > > >>> +     name = devm_kasprintf(&plat_dev->dev, GFP_KERNEL, "dwc_rootport_%d_pmu", sbdf);
> > > > >>
> > > > >> A new name will break previous user tools.
> > > > > This name isn't suitable. It can't clearly show which is the PMU
> > > > > device. Userspace tools don't have binding relationships, like perf.
> > > > > Tools must traverse PMU devices before use.
> > > >
> > > > The device is under /sys/bus/event_source/ which indates it is PMU device.
> > > > As far as I know, most of PMU devices do not endup with a '_pmu' prefix.
> > >
> > > The point is the name "dwc_rootport_" is misleading, suggesting an
> > > extra PCIE RP in the system. Best to change the name to intuitive
> > > "xx_pmu".
> >
> > As pointed out above, changing the name will break userspace. So it's
> > simply not an option, sorry.
> 
> Could you specify what in the userspace is broken and give an example?

Can't I just take the documented example from dwc_pcie_pmu.rst:

$# perf stat -a -e dwc_rootport_13018/Rx_PCIe_TLP_Data_Payload/

If I have a script that uses that command on a machine today, then
applying your kernel patch will break the script, no?

Will