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

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Message-ID: <20241209224741.GA3206765@bhelgaas>
Date: Mon, 9 Dec 2024 16:47:41 -0600
From: Bjorn Helgaas <helgaas@...nel.org>
To: Will Deacon <will@...nel.org>
Cc: Shuai Xue <xueshuai@...ux.alibaba.com>, ilkka@...amperecomputing.com,
	kaishen@...ux.alibaba.com, yangyicong@...wei.com,
	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 Mon, Dec 09, 2024 at 03:40:16PM +0000, Will Deacon wrote:
> On Fri, Dec 06, 2024 at 10:54:57AM -0600, Bjorn Helgaas wrote:
> > On Fri, Dec 08, 2023 at 10:56:51AM +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 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).
> > 
> > > +#define DWC_PCIE_VSEC_RAS_DES_ID		0x02
> > 
> > > +static const struct dwc_pcie_vendor_id dwc_pcie_vendor_ids[] = {
> > > +	{.vendor_id = PCI_VENDOR_ID_ALIBABA },
> > > +	{} /* terminator */
> > > +};
> > 
> > > +static bool dwc_pcie_match_des_cap(struct pci_dev *pdev)
> > > +{
> > > +	const struct dwc_pcie_vendor_id *vid;
> > > +	u16 vsec;
> > > +	u32 val;
> > > +
> > > +	if (!pci_is_pcie(pdev) || !(pci_pcie_type(pdev) == PCI_EXP_TYPE_ROOT_PORT))
> > > +		return false;
> > > +
> > > +	for (vid = dwc_pcie_vendor_ids; vid->vendor_id; vid++) {
> > > +		vsec = pci_find_vsec_capability(pdev, vid->vendor_id,
> > > +						DWC_PCIE_VSEC_RAS_DES_ID);
> > 
> > This looks wrong to me, and it promotes a misunderstanding of how VSEC
> > Capabilities work.  The VSEC ID is defined by the vendor, so we have
> > to check both the Vendor ID and the VSEC ID before we know what this
> > VSEC Capability is.
> 
> Thanks for pointing this out! The code's been merged for a while now,
> so we'll need to fix what we have rather than revert it, I think.

Yep, for sure.

> Any chance you could send a patch with those, please? I'm also not able
> to test this stuff, but I'm sure Ilkka would help us out.

Posted at https://lore.kernel.org/linux-pci/20241209222938.3219364-1-helgaas@kernel.org

Bjorn