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

[Shuai Xue]

On 2023/8/1 19:46, Yicong Yang wrote:
> 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.

I see, but can root port be removed from userspace? I check the hotplug slot interface, no root
port is available to power off.

Thank you.

Best Regards,
Shuai