linux-kernel - Re: [RESEND v13 02/25] PCI/CXL: Introduce pcie_is

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Message-ID: <aSDMId90SsE71p1W@gourry-fedora-PF4VCD3F>
Date: Fri, 21 Nov 2025 15:31:29 -0500
From: Gregory Price <gourry@...rry.net>
To: Terry Bowman <terry.bowman@....com>
Cc: dave@...olabs.net, jonathan.cameron@...wei.com, dave.jiang@...el.com,
	alison.schofield@...el.com, dan.j.williams@...el.com,
	bhelgaas@...gle.com, shiju.jose@...wei.com, ming.li@...omail.com,
	Smita.KoralahalliChannabasappa@....com, rrichter@....com,
	dan.carpenter@...aro.org, PradeepVineshReddy.Kodamati@....com,
	lukas@...ner.de, Benjamin.Cheatham@....com,
	sathyanarayanan.kuppuswamy@...ux.intel.com,
	linux-cxl@...r.kernel.org, alucerop@....com, ira.weiny@...el.com,
	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org
Subject: Re: [RESEND v13 02/25] PCI/CXL: Introduce pcie_is_cxl()

On Tue, Nov 04, 2025 at 11:02:42AM -0600, Terry Bowman wrote:
> CXL and AER drivers need the ability to identify CXL devices.
> 
> Introduce set_pcie_cxl() with logic checking for CXL.mem or CXL.cache
> status in the CXL Flexbus DVSEC status register. The CXL Flexbus DVSEC
> presence is used because it is required for all the CXL PCIe devices.[1]
> 
------>8
>  
> +static void set_pcie_cxl(struct pci_dev *dev)
> +{
> +	struct pci_dev *parent;
...
> +	parent = pci_upstream_bridge(dev);
> +	set_pcie_cxl(parent);
> +}
...
> +static inline bool pcie_is_cxl(struct pci_dev *pci_dev)
> +{
> +	return pci_dev->is_cxl;
> +}
> +

We have encountered a crash on QEMU where parent=NULL here

static inline struct pci_dev *pci_upstream_bridge(struct pci_dev *dev)
{
        dev = pci_physfn(dev);
        if (pci_is_root_bus(dev->bus))
                return NULL;

        return dev->bus->self;
}

~Gregory