Re: [RESEND v13 02/25] PCI/CXL: Introduce pcie_is_cxl()

[Gregory Price]

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