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

Bowman, Terry
2025-01-14T15:19:21Z

On 1/13/2025 5:49 PM, Ira Weiny wrote:
> 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.

Hi Ira,

Thanks for reviewing. Is this what you are looking for here:

+bool pcie_is_cxl_port(struct pci_dev *dev)
+{
+ return (cxl_port_dvsec(dev) > 0);

>> +}
>> +
> [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
Ok,

Thanks for reviewing the patches.

Regards,
Terry
> [snip]