Re: [PATCH v5 03/16] CXL/PCI: Introduce PCIe helper functions pcie_is_cxl() and pcie_is_cxl_port()

Ira Weiny
2025-01-13T23:49:47Z

Terry Bowman wrote:
> CXL and AER drivers need the ability to identify CXL devices and CXL port
> devices.
>
> First, 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 pcie_is_cxl() as a macro to return 'struct pci_dev::is_cxl'.
>
> Add pcie_is_cxl_port() to check if a device is a CXL Root Port, CXL
> Upstream Switch Port, or CXL Downstream Switch Port. Also, verify the
> CXL Extensions DVSEC for Ports is present.[1]
>
> [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: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> Reviewed-by: Dave Jiang <dave.jiang@intel.com>
> Reviewed-by: Fan Ni <fan.ni@samsung.com>
> ---
> drivers/pci/pci.c | 13 +++++++++++++
> drivers/pci/probe.c | 10 ++++++++++
> include/linux/pci.h | 4 ++++
> include/uapi/linux/pci_regs.h | 3 ++-
> 4 files changed, 29 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 661f98c6c63a..9319c62e3488 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -5036,10 +5036,23 @@ static int pci_dev_reset_slot_function(struct pci_dev *dev, bool probe)
>
> static u16 cxl_port_dvsec(struct pci_dev *dev)
> {
> + if (!pcie_is_cxl(dev))
> + return 0;
> +
> return pci_find_dvsec_capability(dev, PCI_VENDOR_ID_CXL,
> PCI_DVSEC_CXL_PORT);
> }
>
> +bool pcie_is_cxl_port(struct pci_dev *dev)
> +{
> + if ((pci_pcie_type(dev) != PCI_EXP_TYPE_ROOT_PORT) &&
> + (pci_pcie_type(dev) != PCI_EXP_TYPE_UPSTREAM) &&
> + (pci_pcie_type(dev) != PCI_EXP_TYPE_DOWNSTREAM))
> + return false;
> +
> + return cxl_port_dvsec(dev);

Returning bool from a function which returns u16 is odd and I don't think
it should be coded this way. I don't think it is wrong right now but this
really ought to code the pcie_is_cxl() here and leave cxl_port_dvsec()
alone. Calling cxl_port_dvsec(), checking for if the dvsec exists, and
returning bool.

> +}
> +

[snip]

> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index e2e36f11205c..08350302b3e9 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -452,6 +452,7 @@ 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
> @@ -739,6 +740,9 @@ static inline bool pci_is_vga(struct pci_dev *pdev)
> return false;
> }
>
> +#define pcie_is_cxl(dev) (dev->is_cxl)

This should be an inline function which takes struct pci_dev * for type
safety.

Ira

[snip]