Re: [PATCH v7 03/17] CXL/PCI: Introduce PCIe helper functions pcie_is_cxl() and pcie_is_cxl_port()

Bowman, Terry
2025-02-11T20:38:54Z

On 2/11/2025 2:28 PM, Bjorn Helgaas wrote:
> On Tue, Feb 11, 2025 at 01:24:30PM -0600, 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>
> Acked-by: Bjorn Helgaas <bhelgaas@google.com>
>
> But I would change the subject to:
>
> PCI/CXL: ...
>
> since this only changes drivers/pci files.

I'll change to PCI/CXL. Thanks for the review and 'acks'.

Terry
>> ---
>> drivers/pci/pci.c | 13 +++++++++++++
>> drivers/pci/probe.c | 10 ++++++++++
>> include/linux/pci.h | 5 +++++
>> include/uapi/linux/pci_regs.h | 3 ++-
>> 4 files changed, 30 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
>> index 869d204a70a3..a2d8b41dd043 100644
>> --- a/drivers/pci/pci.c
>> +++ b/drivers/pci/pci.c
>> @@ -5032,6 +5032,19 @@ static u16 cxl_port_dvsec(struct pci_dev *dev)
>> PCI_DVSEC_CXL_PORT);
>> }
>>
>> +inline bool pcie_is_cxl(struct pci_dev *pci_dev)
>> +{
>> + return pci_dev->is_cxl;
>> +}
>> +
>> +bool pcie_is_cxl_port(struct pci_dev *dev)
>> +{
>> + if (!pcie_is_cxl(dev))
>> + return false;
>> +
>> + return (cxl_port_dvsec(dev) > 0);
>> +}
>> +
>> static bool cxl_sbr_masked(struct pci_dev *dev)
>> {
>> u16 dvsec, reg;
>> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
>> index b6536ed599c3..7737b9ce7a83 100644
>> --- a/drivers/pci/probe.c
>> +++ b/drivers/pci/probe.c
>> @@ -1676,6 +1676,14 @@ 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);
>> @@ -2006,6 +2014,8 @@ 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 1d62e785ae1f..82a0401c58d3 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
>> @@ -741,6 +742,10 @@ static inline bool pci_is_vga(struct pci_dev *pdev)
>> return false;
>> }
>>
>> +bool pcie_is_cxl(struct pci_dev *pci_dev);
>> +
>> +bool pcie_is_cxl_port(struct pci_dev *dev);
>> +
>> #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 3445c4970e4d..dbc0f23d8c82 100644
>> --- a/include/uapi/linux/pci_regs.h
>> +++ b/include/uapi/linux/pci_regs.h
>> @@ -1208,9 +1208,10 @@
>> #define PCI_DOE_DATA_OBJECT_DISC_RSP_3_PROTOCOL 0x00ff0000
>> #define PCI_DOE_DATA_OBJECT_DISC_RSP_3_NEXT_INDEX 0xff000000
>>
>> -/* Compute Express Link (CXL r3.1, sec 8.1.5) */
>> +/* Compute Express Link (CXL r3.1, sec 8.1) */
>> #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 */
>> --
>> 2.34.1
>>