[PATCH v6 07/21] dma-mapping: add flags to dma_map_ops to indicate PCI P2PDMA support

[Logan Gunthorpe]

Add a flags member to the dma_map_ops structure with one flag to
indicate support for PCI P2PDMA.

Also, add a helper to check if a device supports PCI P2PDMA.

Signed-off-by: Logan Gunthorpe <logang@xxxxxxxxxxxx>
Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
---
 include/linux/dma-map-ops.h | 10 ++++++++++
 include/linux/dma-mapping.h |  5 +++++
 kernel/dma/mapping.c        | 18 ++++++++++++++++++
 3 files changed, 33 insertions(+)

diff --git a/include/linux/dma-map-ops.h b/include/linux/dma-map-ops.h
index 752f91e5eb5d..4d4161d58ce0 100644
--- a/include/linux/dma-map-ops.h
+++ b/include/linux/dma-map-ops.h
@@ -11,7 +11,17 @@
 
 struct cma;
 
+/*
+ * Values for struct dma_map_ops.flags:
+ *
+ * DMA_F_PCI_P2PDMA_SUPPORTED: Indicates the dma_map_ops implementation can
+ * handle PCI P2PDMA pages in the map_sg/unmap_sg operation.
+ */
+#define DMA_F_PCI_P2PDMA_SUPPORTED     (1 << 0)
+
 struct dma_map_ops {
+	unsigned int flags;
+
 	void *(*alloc)(struct device *dev, size_t size,
 			dma_addr_t *dma_handle, gfp_t gfp,
 			unsigned long attrs);
diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
index dca2b1355bb1..f7c61b2b4b5e 100644
--- a/include/linux/dma-mapping.h
+++ b/include/linux/dma-mapping.h
@@ -140,6 +140,7 @@ int dma_mmap_attrs(struct device *dev, struct vm_area_struct *vma,
 		unsigned long attrs);
 bool dma_can_mmap(struct device *dev);
 int dma_supported(struct device *dev, u64 mask);
+bool dma_pci_p2pdma_supported(struct device *dev);
 int dma_set_mask(struct device *dev, u64 mask);
 int dma_set_coherent_mask(struct device *dev, u64 mask);
 u64 dma_get_required_mask(struct device *dev);
@@ -250,6 +251,10 @@ static inline int dma_supported(struct device *dev, u64 mask)
 {
 	return 0;
 }
+static inline bool dma_pci_p2pdma_supported(struct device *dev)
+{
+	return false;
+}
 static inline int dma_set_mask(struct device *dev, u64 mask)
 {
 	return -EIO;
diff --git a/kernel/dma/mapping.c b/kernel/dma/mapping.c
index 9f65d1041638..21793506fdb6 100644
--- a/kernel/dma/mapping.c
+++ b/kernel/dma/mapping.c
@@ -722,6 +722,24 @@ int dma_supported(struct device *dev, u64 mask)
 }
 EXPORT_SYMBOL(dma_supported);
 
+bool dma_pci_p2pdma_supported(struct device *dev)
+{
+	const struct dma_map_ops *ops = get_dma_ops(dev);
+
+	/* if ops is not set, dma direct will be used which supports P2PDMA */
+	if (!ops)
+		return true;
+
+	/*
+	 * Note: dma_ops_bypass is not checked here because P2PDMA should
+	 * not be used with dma mapping ops that do not have support even
+	 * if the specific device is bypassing them.
+	 */
+
+	return ops->flags & DMA_F_PCI_P2PDMA_SUPPORTED;
+}
+EXPORT_SYMBOL_GPL(dma_pci_p2pdma_supported);
+
 #ifdef CONFIG_ARCH_HAS_DMA_SET_MASK
 void arch_dma_set_mask(struct device *dev, u64 mask);
 #else
-- 
2.30.2