PCI/P2PDMA: Provide an access to pci_p2pdma_map_type() function

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>
Acked-by: Ankit Agrawal <ankita@nvidia.com>
Link: https://lore.kernel.org/r/20251120-dmabuf-vfio-v9-4-d7f71607f371@nvidia.com
Signed-off-by: Alex Williamson <alex@shazbot.org>

diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
index 855d3493634c381083d5d47ae0e4f5846bc518db..981a76b6b7c0cc586e008b7f29ecd7febcdf201a 100644 (file)
--- 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 15471252817b1e0210e02cbd1b5b4f494896317f..517e121d2598e3d14571b94e47e4bade6beef574 100644 (file)
--- 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;