linux-kernel - Re: [PATCH 2/3] perf/dwc_pcie: Load DesignWare PCIe PMU driver automatically on Ampere SoCs

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Message-ID: <20241028173132.GC2871@willie-the-truck>
Date: Mon, 28 Oct 2024 17:31:34 +0000
From: Will Deacon <will@...nel.org>
To: Ilkka Koskinen <ilkka@...amperecomputing.com>
Cc: Shuai Xue <xueshuai@...ux.alibaba.com>,
	Jing Zhang <renyu.zj@...ux.alibaba.com>,
	Mark Rutland <mark.rutland@....com>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] perf/dwc_pcie: Load DesignWare PCIe PMU driver
 automatically on Ampere SoCs

On Thu, Oct 24, 2024 at 03:19:17PM -0700, Ilkka Koskinen wrote:
> 
> Hi Will,
> 
> On Thu, 24 Oct 2024, Will Deacon wrote:
> > On Tue, Oct 08, 2024 at 11:18:23PM +0000, Ilkka Koskinen wrote:
> > > Load DesignWare PCIe PMU driver automatically if the system has a PCI
> > > bridge by Ampere.
> > > 
> > > Signed-off-by: Ilkka Koskinen <ilkka@...amperecomputing.com>
> > > ---
> > >  drivers/perf/dwc_pcie_pmu.c | 10 ++++++++++
> > >  1 file changed, 10 insertions(+)
> > > 
> > > diff --git a/drivers/perf/dwc_pcie_pmu.c b/drivers/perf/dwc_pcie_pmu.c
> > > index 3581d916d851..d752168733cf 100644
> > > --- a/drivers/perf/dwc_pcie_pmu.c
> > > +++ b/drivers/perf/dwc_pcie_pmu.c
> > > @@ -782,6 +782,16 @@ static void __exit dwc_pcie_pmu_exit(void)
> > >  module_init(dwc_pcie_pmu_init);
> > >  module_exit(dwc_pcie_pmu_exit);
> > > 
> > > +static const struct pci_device_id dwc_pcie_pmu_table[] = {
> > > +	{
> > > +		PCI_DEVICE(PCI_VENDOR_ID_AMPERE, PCI_ANY_ID),
> > > +		.class		= PCI_CLASS_BRIDGE_PCI_NORMAL,
> > > +		.class_mask	= ~0,
> > > +	},
> > > +	{ }
> > > +};
> > > +MODULE_DEVICE_TABLE(pci, dwc_pcie_pmu_table);
> > 
> > Hmm, won't this only work if the driver is modular? Should we be calling
> > pci_register_driver() for the builtin case?
> 
> That would be the normal case indeed. However, this driver is quite
> different: dwc_pcie_pmu_init() goes through all the pci devices looking for
> root ports with the pmu capabilities. Moreover, the probe function isn't
> bound to any specific vendor/class/device IDs. This patch simply makes sure
> the driver is loaded and the init function gets called, if the driver was
> built as module and ran on Ampere system.

Ok, but that seems like the wrong approach, no? We end up with a weird
list of vendors who want the thing to probe on their SoCs and, by
omission, everybody not on the list doesn't want that behaviour.

Will