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

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Message-ID: <20241029130014.GC4241@willie-the-truck>
Date: Tue, 29 Oct 2024 13:00:15 +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 Mon, Oct 28, 2024 at 08:27:27PM -0700, Ilkka Koskinen wrote:
> 
> On Mon, 28 Oct 2024, Will Deacon wrote:
> > 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.
> 
> Ideally, dwc pmu driver would claim the supported root ports but I think the
> PCIe driver is doing that. How about if we simply drop the auto loading
> patch and let users to manually load the driver as they have been doing so
> far?

Sure, I'll pick the other two up. Thanks!

Will