[PATCH v11 08/23] PCI/CXL: Introduce pcie_is_cxl()

Terry Bowman
2025-08-27T01:37:19Z

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 Flexbus DVSEC status register. 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
CXL.cache and CXl.mem status.

In the case the device is an EP or USP, call set_pcie_cxl() on behalf of
the parent downstream device. This will make certain the correct 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>

---
Changes in v10->v11:
- Amended 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 | 25 +++++++++++++++++++++++++
include/linux/pci.h | 6 ++++++
include/uapi/linux/pci_regs.h | 3 +++
3 files changed, 34 insertions(+)

diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index 4b8693ec9e4c..b08cd0346136 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -1691,6 +1691,29 @@ 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 *parent;
+ u16 dvsec = pci_find_dvsec_capability(dev, PCI_VENDOR_ID_CXL,
+ PCI_DVSEC_CXL_FLEXBUS_PORT);
+ if (dvsec) {
+ u16 cap;
+
+ pci_read_config_word(dev, dvsec + PCI_DVSEC_CXL_FLEXBUS_STATUS_OFFSET, &cap);
+
+ dev->is_cxl = FIELD_GET(PCI_DVSEC_CXL_FLEXBUS_STATUS_CACHE_MASK, cap) ||
+ FIELD_GET(PCI_DVSEC_CXL_FLEXBUS_STATUS_MEM_MASK, cap);
+ }
+
+ if (!pci_is_pcie(dev) ||
+ !(pci_pcie_type(dev) == PCI_EXP_TYPE_ENDPOINT ||
+ pci_pcie_type(dev) == PCI_EXP_TYPE_UPSTREAM))
+ return;
+
+ parent = pci_upstream_bridge(dev);
+ set_pcie_cxl(parent);
+}
+
static void set_pcie_untrusted(struct pci_dev *dev)
{
struct pci_dev *parent = pci_upstream_bridge(dev);
@@ -2021,6 +2044,8 @@ 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 05e68f35f392..79878243b681 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -453,6 +453,7 @@ 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
@@ -744,6 +745,11 @@ 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 b03244d55aea..252c06402b13 100644
--- a/include/uapi/linux/pci_regs.h
+++ b/include/uapi/linux/pci_regs.h
@@ -1274,6 +1274,9 @@

/* CXL 3.2 8.1.8: PCIe DVSEC for Flex Bus Port */
#define PCI_DVSEC_CXL_FLEXBUS_PORT 7
+#define PCI_DVSEC_CXL_FLEXBUS_STATUS_OFFSET 0xE
+#define PCI_DVSEC_CXL_FLEXBUS_STATUS_CACHE_MASK BIT(0)
+#define PCI_DVSEC_CXL_FLEXBUS_STATUS_MEM_MASK BIT(2)

/* CXL 3.2 8.1.9: Register Locator DVSEC */
#define PCI_DVSEC_CXL_REG_LOCATOR 8
--
2.51.0.rc2.21.ge5ab6b3e5a