On Wed, Jan 14, 2026 at 12:20:24PM -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 Flex Bus DVSEC status register. The CXL Flex Bus 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
> CXL.cache and CXl.mem status.
>
> Call set_pcie_cxl() for the parent bridge. Once a device is created there
> is a possibility the parent training or CXL state was updated as well. This
> will make certain the correct parent CXL state is cached.
>
> 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>
> Reviewed-by: Dave Jiang <dave.jiang@intel.com>
> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> Reviewed-by: Alejandro Lucero <alucerop@amd.com>
> Reviewed-by: Ben Cheatham <benjamin.cheatham@amd.com>
> Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>
> ---
>
> Changes in v13->v14:
> - Move FLEXBUS_STATUS DVSEC here (Jonathan)
> - Remove check for EP and USP (Dan)
> - Update commit message (Bjorn)
> - Fix writing past 80 columns (Bjorn)
> - Add pci_is_pcie() parent bridge check at beginning of function (Bjorn)
>
> Changes in v12->v13:
> - Add Ben's "reviewed-by"
>
> Changes in v11->v12:
> - Add review-by for Alejandro
> - Add comment in set_pcie_cxl() explaining why updating parent status.
>
> Changes in v10->v11:
> - Amend set_pcie_cxl() to check for Upstream Port's and EP's parent
> downstream port by calling set_pcie_cxl(). (Dan)
> - Retitle patch: 'Add' -> 'Introduce'
> - Add check for CXL.mem and CXL.cache (Alejandro, Dan)
> ---
> drivers/pci/probe.c | 31 +++++++++++++++++++++++++++++++
> include/linux/pci.h | 6 ++++++
> include/uapi/linux/pci_regs.h | 6 ++++++
> 3 files changed, 43 insertions(+)
>
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index 41183aed8f5d..bd7ce41d0c7a 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -1735,6 +1735,35 @@ static void set_pcie_thunderbolt(struct pci_dev *dev)
> dev->is_thunderbolt = 1;
> }
>
> +static void set_pcie_cxl(struct pci_dev *dev)
> +{
> + struct pci_dev *bridge;
> + u16 dvsec, cap;
> +
> + if (!pci_is_pcie(dev))
> + return;
> +
> + /*
> + * Update parent's CXL state because alternate protocol training
> + * may have changed
> + */
> + bridge = pci_upstream_bridge(dev);
> + if (bridge)
> + set_pcie_cxl(bridge);
> +
> + dvsec = pci_find_dvsec_capability(dev, PCI_VENDOR_ID_CXL,
> + PCI_DVSEC_CXL_FLEXBUS_PORT);
> + if (!dvsec)
> + return;
> +
> + pci_read_config_word(dev, dvsec + PCI_DVSEC_CXL_FLEXBUS_PORT_STATUS,
> + &cap);
> +
> + dev->is_cxl = FIELD_GET(PCI_DVSEC_CXL_FLEXBUS_PORT_STATUS_CACHE, cap) ||
> + FIELD_GET(PCI_DVSEC_CXL_FLEXBUS_PORT_STATUS_MEM, cap);
> +
> +}
> +
> static void set_pcie_untrusted(struct pci_dev *dev)
> {
> struct pci_dev *parent = pci_upstream_bridge(dev);
> @@ -2065,6 +2094,8 @@ 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 864775651c6f..f8e8b3df794d 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -463,6 +463,7 @@ struct pci_dev {
> unsigned int is_pciehp: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
> @@ -791,6 +792,11 @@ static inline bool pci_is_display(struct pci_dev *pdev)
> return (pdev->class >> 16) == PCI_BASE_CLASS_DISPLAY;
> }
>
> +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 662582bdccf0..b6622fd60fd9 100644
> --- a/include/uapi/linux/pci_regs.h
> +++ b/include/uapi/linux/pci_regs.h
> @@ -1379,6 +1379,12 @@
> /* CXL r4.0, 8.1.7: GPF DVSEC for CXL Device */
> #define PCI_DVSEC_CXL_DEVICE_GPF 5
>
> +/* CXL r4.0, 8.1.8: Flex Bus DVSEC */
> +#define PCI_DVSEC_CXL_FLEXBUS_PORT 7
> +#define PCI_DVSEC_CXL_FLEXBUS_PORT_STATUS 0xE
> +#define PCI_DVSEC_CXL_FLEXBUS_PORT_STATUS_CACHE _BITUL(0)
> +#define PCI_DVSEC_CXL_FLEXBUS_PORT_STATUS_MEM _BITUL(2)
> +
> /* CXL r4.0, 8.1.9: Register Locator DVSEC */
> #define PCI_DVSEC_CXL_REG_LOCATOR 8
> #define PCI_DVSEC_CXL_REG_LOCATOR_BLOCK1 0xC
> --
> 2.34.1
>