Re: [PATCH v9 01/16] PCI/CXL: Add pcie_is_cxl()

[Sathyanarayanan Kuppuswamy <sathyanarayanan.kuppuswamy@linux.intel.com>]

On 6/3/25 10:22 AM, Terry Bowman wrote:
> CXL and AER drivers need the ability to identify CXL devices.
>
> Add set_pcie_cxl() with logic checking for CXL Flexbus DVSEC presence. The
> CXL Flexbus DVSEC presence is used because it is required for all the CXL
> PCIe devices.[1]
>
> Add boolean 'struct pci_dev::is_cxl' with the purpose to cache the CXL
> Flexbus presence.
>
> Add function pcie_is_cxl() to return 'struct pci_dev::is_cxl'.
>
> [1] CXL 3.1 Spec, 8.1.1 PCIe Designated Vendor-Specific Extended
>      Capability (DVSEC) ID Assignment, Table 8-2
>
> Signed-off-by: Terry Bowman <terry.bowman@amd.com>
> Reviewed-by: Ira Weiny <ira.weiny@intel.com>
> ---

Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>

>   drivers/pci/probe.c           | 10 ++++++++++
>   include/linux/pci.h           |  6 ++++++
>   include/uapi/linux/pci_regs.h |  8 +++++++-
>   3 files changed, 23 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index 364fa2a514f8..aa29b4b98ad1 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -1691,6 +1691,14 @@ static void set_pcie_thunderbolt(struct pci_dev *dev)
>   		dev->is_thunderbolt = 1;
>   }
>   
> +static void set_pcie_cxl(struct pci_dev *dev)
> +{
> +	u16 dvsec = pci_find_dvsec_capability(dev, PCI_VENDOR_ID_CXL,
> +					      PCI_DVSEC_CXL_FLEXBUS);
> +	if (dvsec)
> +		dev->is_cxl = 1;
> +}
> +
>   static void set_pcie_untrusted(struct pci_dev *dev)
>   {
>   	struct pci_dev *parent = pci_upstream_bridge(dev);
> @@ -2021,6 +2029,8 @@ int pci_setup_device(struct pci_dev *dev)
>   	/* Need to have dev->cfg_size ready */
>   	set_pcie_thunderbolt(dev);
>   
> +	set_pcie_cxl(dev);
> +
>   	set_pcie_untrusted(dev);
>   
>   	if (pci_is_pcie(dev))
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index 51e2bd6405cd..bff3009f9ff0 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -455,6 +455,7 @@ struct pci_dev {
>   	unsigned int	is_hotplug_bridge:1;
>   	unsigned int	shpc_managed:1;		/* SHPC owned by shpchp */
>   	unsigned int	is_thunderbolt:1;	/* Thunderbolt controller */
> +	unsigned int	is_cxl:1;               /* Compute Express Link (CXL) */
>   	/*
>   	 * Devices marked being untrusted are the ones that can potentially
>   	 * execute DMA attacks and similar. They are typically connected
> @@ -746,6 +747,11 @@ static inline bool pci_is_vga(struct pci_dev *pdev)
>   	return false;
>   }
>   
> +static inline bool pcie_is_cxl(struct pci_dev *pci_dev)
> +{
> +	return pci_dev->is_cxl;
> +}
> +
>   #define for_each_pci_bridge(dev, bus)				\
>   	list_for_each_entry(dev, &bus->devices, bus_list)	\
>   		if (!pci_is_bridge(dev)) {} else
> diff --git a/include/uapi/linux/pci_regs.h b/include/uapi/linux/pci_regs.h
> index ba326710f9c8..c50ffa75d5fc 100644
> --- a/include/uapi/linux/pci_regs.h
> +++ b/include/uapi/linux/pci_regs.h
> @@ -1215,9 +1215,15 @@
>   /* Deprecated old name, replaced with PCI_DOE_DATA_OBJECT_DISC_RSP_3_TYPE */
>   #define PCI_DOE_DATA_OBJECT_DISC_RSP_3_PROTOCOL		PCI_DOE_DATA_OBJECT_DISC_RSP_3_TYPE
>   
> -/* Compute Express Link (CXL r3.1, sec 8.1.5) */
> +/* Compute Express Link (CXL r3.2, sec 8.1)
> + *
> + * Note that CXL DVSEC id 3 and 7 to be ignored when the CXL link state
> + * is "disconnected" (CXL r3.2, sec 9.12.3). Re-enumerate these
> + * registers on downstream link-up events.
> + */
>   #define PCI_DVSEC_CXL_PORT				3
>   #define PCI_DVSEC_CXL_PORT_CTL				0x0c
>   #define PCI_DVSEC_CXL_PORT_CTL_UNMASK_SBR		0x00000001
> +#define PCI_DVSEC_CXL_FLEXBUS				7
>   
>   #endif /* LINUX_PCI_REGS_H */

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer