[PATCH v9 04/11] PCI/P2PDMA: Provide an access to pci_p2pdma_map_type() function

Leon Romanovsky
2025-11-20T09:29:00Z

From: Leon Romanovsky <leonro@nvidia.com>

Provide an access to pci_p2pdma_map_type() function to allow subsystems
to determine the appropriate mapping type for P2PDMA transfers between
a provider and target device.

The pci_p2pdma_map_type() function is the core P2P layer version of
the existing public, but struct page focused, pci_p2pdma_state()
function. It returns the same result. It is required to use the p2p
subsystem from drivers that don't use the struct page layer.

Like __pci_p2pdma_update_state() it is not an exported function. The
idea is that only subsystem code will implement mapping helpers for
taking in phys_addr_t lists, this is deliberately not made accessible
to every driver to prevent abuse.

Following patches will use this function to implement a shared DMA
mapping helper for DMABUF.

Tested-by: Alex Mastro <amastro@fb.com>
Tested-by: Nicolin Chen <nicolinc@nvidia.com>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
---
drivers/pci/p2pdma.c | 14 ++++++--
include/linux/pci-p2pdma.h | 85 +++++++++++++++++++++++++---------------------
2 files changed, 58 insertions(+), 41 deletions(-)

diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
index 855d3493634c..981a76b6b7c0 100644
--- a/drivers/pci/p2pdma.c
+++ b/drivers/pci/p2pdma.c
@@ -1060,8 +1060,18 @@ void pci_p2pmem_publish(struct pci_dev *pdev, bool publish)
}
EXPORT_SYMBOL_GPL(pci_p2pmem_publish);

-static enum pci_p2pdma_map_type
-pci_p2pdma_map_type(struct p2pdma_provider *provider, struct device *dev)
+/**
+ * pci_p2pdma_map_type - Determine the mapping type for P2PDMA transfers
+ * @provider: P2PDMA provider structure
+ * @dev: Target device for the transfer
+ *
+ * Determines how peer-to-peer DMA transfers should be mapped between
+ * the provider and the target device. The mapping type indicates whether
+ * the transfer can be done directly through PCI switches or must go
+ * through the host bridge.
+ */
+enum pci_p2pdma_map_type pci_p2pdma_map_type(struct p2pdma_provider *provider,
+ struct device *dev)
{
enum pci_p2pdma_map_type type = PCI_P2PDMA_MAP_NOT_SUPPORTED;
struct pci_dev *pdev = to_pci_dev(provider->owner);
diff --git a/include/linux/pci-p2pdma.h b/include/linux/pci-p2pdma.h
index 15471252817b..517e121d2598 100644
--- a/include/linux/pci-p2pdma.h
+++ b/include/linux/pci-p2pdma.h
@@ -26,6 +26,45 @@ struct p2pdma_provider {
u64 bus_offset;
};

+enum pci_p2pdma_map_type {
+ /*
+ * PCI_P2PDMA_MAP_UNKNOWN: Used internally as an initial state before
+ * the mapping type has been calculated. Exported routines for the API
+ * will never return this value.
+ */
+ PCI_P2PDMA_MAP_UNKNOWN = 0,
+
+ /*
+ * Not a PCI P2PDMA transfer.
+ */
+ PCI_P2PDMA_MAP_NONE,
+
+ /*
+ * PCI_P2PDMA_MAP_NOT_SUPPORTED: Indicates the transaction will
+ * traverse the host bridge and the host bridge is not in the
+ * allowlist. DMA Mapping routines should return an error when
+ * this is returned.
+ */
+ PCI_P2PDMA_MAP_NOT_SUPPORTED,
+
+ /*
+ * PCI_P2PDMA_MAP_BUS_ADDR: Indicates that two devices can talk to
+ * each other directly through a PCI switch and the transaction will
+ * not traverse the host bridge. Such a mapping should program
+ * the DMA engine with PCI bus addresses.
+ */
+ PCI_P2PDMA_MAP_BUS_ADDR,
+
+ /*
+ * PCI_P2PDMA_MAP_THRU_HOST_BRIDGE: Indicates two devices can talk
+ * to each other, but the transaction traverses a host bridge on the
+ * allowlist. In this case, a normal mapping either with CPU physical
+ * addresses (in the case of dma-direct) or IOVA addresses (in the
+ * case of IOMMUs) should be used to program the DMA engine.
+ */
+ PCI_P2PDMA_MAP_THRU_HOST_BRIDGE,
+};
+
#ifdef CONFIG_PCI_P2PDMA
int pcim_p2pdma_init(struct pci_dev *pdev);
struct p2pdma_provider *pcim_p2pdma_provider(struct pci_dev *pdev, int bar);
@@ -45,6 +84,8 @@ int pci_p2pdma_enable_store(const char *page, struct pci_dev **p2p_dev,
bool *use_p2pdma);
ssize_t pci_p2pdma_enable_show(char *page, struct pci_dev *p2p_dev,
bool use_p2pdma);
+enum pci_p2pdma_map_type pci_p2pdma_map_type(struct p2pdma_provider *provider,
+ struct device *dev);
#else /* CONFIG_PCI_P2PDMA */
static inline int pcim_p2pdma_init(struct pci_dev *pdev)
{
@@ -106,6 +147,11 @@ static inline ssize_t pci_p2pdma_enable_show(char *page,
{
return sprintf(page, "none\n");
}
+static inline enum pci_p2pdma_map_type
+pci_p2pdma_map_type(struct p2pdma_provider *provider, struct device *dev)
+{
+ return PCI_P2PDMA_MAP_NOT_SUPPORTED;
+}
#endif /* CONFIG_PCI_P2PDMA */

@@ -120,45 +166,6 @@ static inline struct pci_dev *pci_p2pmem_find(struct device *client)
return pci_p2pmem_find_many(&client, 1);
}

-enum pci_p2pdma_map_type {
- /*
- * PCI_P2PDMA_MAP_UNKNOWN: Used internally as an initial state before
- * the mapping type has been calculated. Exported routines for the API
- * will never return this value.
- */
- PCI_P2PDMA_MAP_UNKNOWN = 0,
-
- /*
- * Not a PCI P2PDMA transfer.
- */
- PCI_P2PDMA_MAP_NONE,
-
- /*
- * PCI_P2PDMA_MAP_NOT_SUPPORTED: Indicates the transaction will
- * traverse the host bridge and the host bridge is not in the
- * allowlist. DMA Mapping routines should return an error when
- * this is returned.
- */
- PCI_P2PDMA_MAP_NOT_SUPPORTED,
-
- /*
- * PCI_P2PDMA_MAP_BUS_ADDR: Indicates that two devices can talk to
- * each other directly through a PCI switch and the transaction will
- * not traverse the host bridge. Such a mapping should program
- * the DMA engine with PCI bus addresses.
- */
- PCI_P2PDMA_MAP_BUS_ADDR,
-
- /*
- * PCI_P2PDMA_MAP_THRU_HOST_BRIDGE: Indicates two devices can talk
- * to each other, but the transaction traverses a host bridge on the
- * allowlist. In this case, a normal mapping either with CPU physical
- * addresses (in the case of dma-direct) or IOVA addresses (in the
- * case of IOMMUs) should be used to program the DMA engine.
- */
- PCI_P2PDMA_MAP_THRU_HOST_BRIDGE,
-};
-
struct pci_p2pdma_map_state {
struct p2pdma_provider *mem;
enum pci_p2pdma_map_type map;

--
2.51.1