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

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Message-ID: <617bffb7-9dee-6139-53d5-524ba03197f6@os.amperecomputing.com>
Date: Thu, 24 Oct 2024 15:19:17 -0700 (PDT)
From: Ilkka Koskinen <ilkka@...amperecomputing.com>
To: Will Deacon <will@...nel.org>
cc: Ilkka Koskinen <ilkka@...amperecomputing.com>, 
    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


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.

Cheers, Ilkka

>
> Will
>