[PATCH 3/5] PCI: Add virtual extended cap save buffer for CXL state

smadhavan
2026-03-06T08:01:10Z

From: Srirangan Madhavan <smadhavan@nvidia.com>

Add pci_add_virtual_ext_cap_save_buffer() to allocate save buffers
using virtual cap IDs (above PCI_EXT_CAP_ID_MAX) that don't require
a real capability in config space.

The existing pci_add_ext_cap_save_buffer() cannot be used for
CXL DVSEC state because it calls pci_find_saved_ext_cap()
which searches for a matching capability in PCI config space.
The CXL state saved here is a synthetic snapshot (DVSEC+HDM)
and should not be tied to a real extended-cap instance. A
virtual extended-cap save buffer API (cap IDs above
PCI_EXT_CAP_ID_MAX) allows PCI to track this state without
a backing config space capability.

Signed-off-by: Srirangan Madhavan <smadhavan@nvidia.com>
---
drivers/pci/pci.c | 20 ++++++++++++++++++++
drivers/pci/pci.h | 18 ++++++++++++++++++
2 files changed, 38 insertions(+)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 8479c2e1f74f..dc8181f13864 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -3446,6 +3446,26 @@ int pci_add_ext_cap_save_buffer(struct pci_dev *dev, u16 cap, unsigned int size)
return _pci_add_cap_save_buffer(dev, cap, true, size);
}

+int pci_add_virtual_ext_cap_save_buffer(struct pci_dev *dev, u16 cap,
+ unsigned int size)
+{
+ struct pci_cap_saved_state *save_state;
+
+ if (cap <= PCI_EXT_CAP_ID_MAX)
+ return -EINVAL;
+
+ save_state = kzalloc(sizeof(*save_state) + size, GFP_KERNEL);
+ if (!save_state)
+ return -ENOMEM;
+
+ save_state->cap.cap_nr = cap;
+ save_state->cap.cap_extended = true;
+ save_state->cap.size = size;
+ pci_add_saved_cap(dev, save_state);
+
+ return 0;
+}
+
/**
* pci_allocate_cap_save_buffers - allocate buffers for saving capabilities
* @dev: the PCI device
diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
index 13d998fbacce..05c57f1e4701 100644
--- a/drivers/pci/pci.h
+++ b/drivers/pci/pci.h
@@ -245,15 +245,33 @@ struct pci_cap_saved_state {
struct pci_cap_saved_data cap;
};

+/*
+ * Virtual extended cap ID for CXL DVSEC state in the cap save chain.
+ */
+#define PCI_EXT_CAP_ID_CXL_DVSEC_VIRTUAL 0xFFFF
+static_assert(PCI_EXT_CAP_ID_MAX < PCI_EXT_CAP_ID_CXL_DVSEC_VIRTUAL);
+
void pci_allocate_cap_save_buffers(struct pci_dev *dev);
void pci_free_cap_save_buffers(struct pci_dev *dev);
int pci_add_cap_save_buffer(struct pci_dev *dev, char cap, unsigned int size);
int pci_add_ext_cap_save_buffer(struct pci_dev *dev,
u16 cap, unsigned int size);
+int pci_add_virtual_ext_cap_save_buffer(struct pci_dev *dev, u16 cap,
+ unsigned int size);
struct pci_cap_saved_state *pci_find_saved_cap(struct pci_dev *dev, char cap);
struct pci_cap_saved_state *pci_find_saved_ext_cap(struct pci_dev *dev,
u16 cap);

+#ifdef CONFIG_PCI_CXL
+void pci_allocate_cxl_save_buffer(struct pci_dev *dev);
+void pci_save_cxl_state(struct pci_dev *dev);
+void pci_restore_cxl_state(struct pci_dev *dev);
+#else
+static inline void pci_allocate_cxl_save_buffer(struct pci_dev *dev) { }
+static inline void pci_save_cxl_state(struct pci_dev *dev) { }
+static inline void pci_restore_cxl_state(struct pci_dev *dev) { }
+#endif
+
#define PCI_PM_D2_DELAY 200 /* usec; see PCIe r4.0, sec 5.9.1 */
#define PCI_PM_D3HOT_WAIT 10 /* msec */
#define PCI_PM_D3COLD_WAIT 100 /* msec */
--
2.43.0