linux-kernel - Re: [PATCH v7 3/4] drivers/perf: add DesignWare PCIe PMU driver

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Message-ID: <20231016143805.GA1207929@bhelgaas>
Date:   Mon, 16 Oct 2023 09:38:05 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Shuai Xue <xueshuai@...ux.alibaba.com>
Cc:     chengyou@...ux.alibaba.com, kaishen@...ux.alibaba.com,
        yangyicong@...wei.com, will@...nel.org,
        Jonathan.Cameron@...wei.com, baolin.wang@...ux.alibaba.com,
        robin.murphy@....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 v7 3/4] drivers/perf: add DesignWare PCIe PMU driver

On Mon, Oct 16, 2023 at 11:00:13AM +0800, Shuai Xue wrote:
> On 2023/10/14 00:30, Bjorn Helgaas wrote:
> > On Fri, Oct 13, 2023 at 11:46:44AM +0800, Shuai Xue wrote:
> >> On 2023/10/13 00:25, Bjorn Helgaas wrote:
> >>> On Thu, Oct 12, 2023 at 11:28:55AM +0800, 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.

> @@ -447,10 +447,10 @@ static int dwc_pcie_pmu_event_add(struct perf_event *event, int flags)
>  	u32 ctrl;
> 
>  	/* Only one counter and it is in use */
> -	if (pcie_pmu->event)
> +	if (pcie_pmu->event[type])
>  		return -ENOSPC;
> 
> -	pcie_pmu->event = event;
> +	pcie_pmu->event[type] = event;

OK, makes good sense (probably update the comment also, e.g., "one
counter of each type").

>  }
> > If so, I might word this as:
> > 
> >   Each Root Port contains one counter that can be used for either:
> > 
> >     - Time-Based Analysis (RX/TX data throughput and time spent in
> >       each low-power LTSSM state) or
> > 
> >     - Event counting (error and non-error events for a specified lane)
> > 
> >   There is no interrupt for counter overflow.
> 
> Based on above, I change the word to:
> 
> 	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.

Beautiful, that's very clear.

Bjorn