linux-kernel - Re: [PATCH v12 4/5] drivers/perf: add DesignWare PCIe PMU driver

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Message-ID: <2bbd5a57-b2ce-6e52-ebf-5935335c148@os.amperecomputing.com>
Date:   Tue, 12 Dec 2023 16:32:56 -0800 (PST)
From:   Ilkka Koskinen <ilkka@...amperecomputing.com>
To:     Shuai Xue <xueshuai@...ux.alibaba.com>
cc:     ilkka@...amperecomputing.com, kaishen@...ux.alibaba.com,
        helgaas@...nel.org, yangyicong@...wei.com, will@...nel.org,
        Jonathan.Cameron@...wei.com, baolin.wang@...ux.alibaba.com,
        robin.murphy@....com, chengyou@...ux.alibaba.com,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-pci@...r.kernel.org, rdunlap@...radead.org,
        mark.rutland@....com, zhuo.song@...ux.alibaba.com,
        renyu.zj@...ux.alibaba.com
Subject: Re: [PATCH v12 4/5] drivers/perf: add DesignWare PCIe PMU driver


On Fri, 8 Dec 2023, 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 a PCIe
> configuration space register block provided by each PCIe Root Port in a
> Vendor-Specific Extended Capability named RAS D.E.S (Debug, Error
> injection, and Statistics).
>
> To facilitate collection of statistics the controller provides the
> following two features for each Root Port:
>
> - one 64-bit counter for Time Based Analysis (RX/TX data throughput and
>  time spent in each low-power LTSSM state) and
> - one 32-bit counter for Event Counting (error and non-error events for
>  a specified lane)
>
> Note: There is no interrupt for counter overflow.
>
> 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 bytes)::
>
>    $# perf stat -a -e dwc_rootport_3018/Rx_PCIe_TLP_Data_Payload/
>
> average RX bandwidth can be calculated like this:
>
>    PCIe TX Bandwidth = Rx_PCIe_TLP_Data_Payload / Measure_Time_Window
>
> Signed-off-by: Shuai Xue <xueshuai@...ux.alibaba.com>
> Reviewed-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
> Reviewed-by: Yicong Yang <yangyicong@...ilicon.com>
> Reviewed-and-tested-by: Ilkka Koskinen <ilkka@...amperecomputing.com>
> ---
> drivers/perf/Kconfig        |   7 +
> drivers/perf/Makefile       |   1 +
> drivers/perf/dwc_pcie_pmu.c | 792 ++++++++++++++++++++++++++++++++++++
> 3 files changed, 800 insertions(+)
> create mode 100644 drivers/perf/dwc_pcie_pmu.c
>
> diff --git a/drivers/perf/dwc_pcie_pmu.c b/drivers/perf/dwc_pcie_pmu.c
> new file mode 100644
> index 000000000000..6ee66c4b44bf
> --- /dev/null
> +++ b/drivers/perf/dwc_pcie_pmu.c
> @@ -0,0 +1,792 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Synopsys DesignWare PCIe PMU driver
> + *
> + * Copyright (C) 2021-2023 Alibaba Inc.
> + */
> +

...

> +static int dwc_pcie_pmu_event_init(struct perf_event *event)
> +{
> +	struct dwc_pcie_pmu *pcie_pmu = to_dwc_pcie_pmu(event->pmu);
> +	enum dwc_pcie_event_type type = DWC_PCIE_EVENT_TYPE(event);
> +	struct perf_event *sibling;
> +	u32 lane;
> +
> +	if (event->attr.type != event->pmu->type)
> +		return -ENOENT;
> +
> +	/* We don't support sampling */
> +	if (is_sampling_event(event))
> +		return -EINVAL;
> +
> +	/* We cannot support task bound events */
> +	if (event->cpu < 0 || event->attach_state & PERF_ATTACH_TASK)
> +		return -EINVAL;
> +
> +	if (event->group_leader != event &&
> +	    !is_software_event(event->group_leader))
> +		return -EINVAL;
> +
> +	for_each_sibling_event(sibling, event->group_leader) {
> +		if (sibling->pmu != event->pmu && !is_software_event(sibling))
> +			return -EINVAL;
> +	}
> +
> +	if (type < 0 || type >= DWC_PCIE_EVENT_TYPE_MAX)
> +		return -EINVAL;
> +
> +	if (type == DWC_PCIE_LANE_EVENT) {
> +		lane = DWC_PCIE_EVENT_LANE(event);
> +		if (lane < 0 || lane >= pcie_pmu->nr_lanes)

Just a minor thing that doesn't really matter: 'lane' is unsigned and, 
therefore, cannot be negative.

Otherwise, everything looks good and seems to work fine still.

Cheers, Ilkka