Re: [PATCH v6 3/4] drivers/perf: add DesignWare PCIe PMU driver

[Yicong Yang]

On 2023/7/28 20:41, Shuai Xue wrote:
> 
> 
> On 2023/7/27 17:39, Jonathan Cameron wrote:
>> On Tue, 6 Jun 2023 23:14:07 +0800
>> Yicong Yang <yangyicong@xxxxxxxxxx> wrote:
>>
>>> On 2023/6/6 15:49, Shuai Xue wrote:
>>>> This commit adds the PCIe Performance Monitoring Unit (PMU) driver support
>>>> for T-Head Yitian SoC chip. Yitian is based on the Synopsys PCI Express
>>>> Core controller IP which provides statistics feature. The PMU is not a PCIe
>>>> Root Complex integrated End Point(RCiEP) device but only register counters
>>>> provided by each PCIe Root Port.
>>>>
>>>> To facilitate collection of statistics the controller provides the
>>>> following two features for each Root Port:
>>>>
>>>> - Time Based Analysis (RX/TX data throughput and time spent in each
>>>>   low-power LTSSM state)
>>>> - Event counters (Error and Non-Error for lanes)
>>>>
>>>> Note, only one counter for each type and does not overflow interrupt.
>>>>
>>>> This driver adds PMU devices for each PCIe Root Port. And the PMU device is
>>>> named based the BDF of Root Port. For example,
>>>>
>>>>     30:03.0 PCI bridge: Device 1ded:8000 (rev 01)
>>>>
>>>> the PMU device name for this Root Port is dwc_rootport_3018.
>>>>
>>>> Example usage of counting PCIe RX TLP data payload (Units of 16 bytes)::
>>>>
>>>>     $# perf stat -a -e dwc_rootport_3018/Rx_PCIe_TLP_Data_Payload/
>>>>
>>>> average RX bandwidth can be calculated like this:
>>>>
>>>>     PCIe TX Bandwidth = PCIE_TX_DATA * 16B / Measure_Time_Window
>>>>
>>>> Signed-off-by: Shuai Xue <xueshuai@xxxxxxxxxxxxxxxxx>
>>>> Reported-by: kernel test robot <lkp@xxxxxxxxx>
>>>> Link: https://lore.kernel.org/oe-kbuild-all/202305170639.XU3djFZX-lkp@xxxxxxxxx/
>>>> Reviewed-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
>>
>> I'll review on top to avoid any duplication with Yicong.
> 
> Thank you! It also served as a reminder that I missed Yicong's email. It appears
> that Thunderbird mistakenly moved his email to the junk folder, resulting in me
> overlooking it.
> 
>>
>> Note I've cropped the stuff neither of us commented on so it's
>> easier to spot the feedback.
> 
> Thank you for noting that. My feedback is replied inline.
> 
>>
>> Jonathan
>>
>>>> ---
>>>>  drivers/perf/Kconfig        |   7 +
>>>>  drivers/perf/Makefile       |   1 +
>>>>  drivers/perf/dwc_pcie_pmu.c | 706 ++++++++++++++++++++++++++++++++++++
>>>>  3 files changed, 714 insertions(+)
>>>>  create mode 100644 drivers/perf/dwc_pcie_pmu.c
>>>>
>>>> diff --git a/drivers/perf/Kconfig b/drivers/perf/Kconfig
>>>> index 711f82400086..6ff3921d7a62 100644
>>>> --- a/drivers/perf/Kconfig
>>>> +++ b/drivers/perf/Kconfig
>>>> @@ -209,6 +209,13 @@ config MARVELL_CN10K_DDR_PMU
>>>>  	  Enable perf support for Marvell DDR Performance monitoring
>>>>  	  event on CN10K platform.
>>>>  
>>>> +config DWC_PCIE_PMU
>>>> +	tristate "Enable Synopsys DesignWare PCIe PMU Support"
>>>> +	depends on (ARM64 && PCI)
>>>> +	help
>>>> +	  Enable perf support for Synopsys DesignWare PCIe PMU Performance
>>>> +	  monitoring event on Yitian 710 platform.
>>
>> The documentation kind of implies this isn't platform specific.
>> If some parts are (such as which events exist) then you may want to push
>> that to userspace / perftool with appropriate matching against specific SoC.
>>
>> If it is generic, then change this text to "event on platform including the Yitian 710."
> 
> It is generic without any platform specific, so I will change it as you expected.
> 
>>
>>>> +
>>>>  source "drivers/perf/arm_cspmu/Kconfig"
>>>>  
>>>>  source "drivers/perf/amlogic/Kconfig"
>>
>>>> new file mode 100644
>>>> index 000000000000..8bfcf6e0662d
>>>> --- /dev/null
>>>> +++ b/drivers/perf/dwc_pcie_pmu.c
>>>> @@ -0,0 +1,706 @@
>>
>> ...
>>
>>>> +
>>>> +struct dwc_pcie_pmu {
>>>> +	struct pci_dev		*pdev;		/* Root Port device */  
>>>
>>> If the root port removed after the probe of this PCIe PMU driver, we'll access the NULL
>>> pointer. I didn't see you hold the root port to avoid the removal.
> 
> Do you mean that I should have a reference count of rootport by pci_dev_get() when allocating
> pcie_pmu?
> 
>      pcie_pmu->pdev = pci_dev_get();

It could be one option, but will block the removal of device from userspace. Another option
is to register a PCI bus notifier then on removal/added the driver can get notified and handle
it, for example, remove the related PMU on the removal of the root ports.