[PATCH v2 14/22] PCI/P2PDMA: Introduce helpers for dma_map_sg implementations

[Logan Gunthorpe]

Add pci_p2pdma_map_segment() as a helper for simple dma_map_sg()
implementations. It takes an scatterlist segment that must point to a
pci_p2pdma struct page and will map it if the mapping requires a bus
address.

The return value indicates whether the mapping required a bus address
or whether the caller still needs to map the segment normally. If the
segment should not be mapped, -EREMOTEIO is returned.

This helper uses a state structure to track the changes to the
pgmap across calls and avoid needing to lookup into the xarray for
every page.

Also add pci_p2pdma_map_bus_segment() which is useful for IOMMU
dma_map_sg() implementations where the sg segment containing the page
differs from the sg segment containing the DMA address.

Signed-off-by: Logan Gunthorpe <logang@xxxxxxxxxxxx>
---
 drivers/pci/p2pdma.c       | 59 ++++++++++++++++++++++++++++++++++++++
 include/linux/pci-p2pdma.h | 21 ++++++++++++++
 2 files changed, 80 insertions(+)

diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
index 0568604fd8b4..b0d779aeade9 100644
--- a/drivers/pci/p2pdma.c
+++ b/drivers/pci/p2pdma.c
@@ -938,6 +938,65 @@ void pci_p2pdma_unmap_sg_attrs(struct device *dev, struct scatterlist *sg,
 }
 EXPORT_SYMBOL_GPL(pci_p2pdma_unmap_sg_attrs);
 
+/**
+ * pci_p2pdma_map_segment - map an sg segment determining the mapping type
+ * @state: State structure that should be declared outside of the for_each_sg()
+ *	loop and initialized to zero.
+ * @dev: DMA device that's doing the mapping operation
+ * @sg: scatterlist segment to map
+ *
+ * This is a helper to be used by non-iommu dma_map_sg() implementations where
+ * the sg segment is the same for the page_link and the dma_address.
+ *
+ * Attempt to map a single segment in an SGL with the PCI bus address.
+ * The segment must point to a PCI P2PDMA page and thus must be
+ * wrapped in a is_pci_p2pdma_page(sg_page(sg)) check.
+ *
+ * Returns the type of mapping used and maps the page if the type is
+ * PCI_P2PDMA_MAP_BUS_ADDR.
+ */
+enum pci_p2pdma_map_type
+pci_p2pdma_map_segment(struct pci_p2pdma_map_state *state, struct device *dev,
+		       struct scatterlist *sg)
+{
+	if (state->pgmap != sg_page(sg)->pgmap) {
+		state->pgmap = sg_page(sg)->pgmap;
+		state->map = pci_p2pdma_map_type(state->pgmap, dev);
+		state->bus_off = to_p2p_pgmap(state->pgmap)->bus_offset;
+	}
+
+	if (state->map == PCI_P2PDMA_MAP_BUS_ADDR) {
+		sg->dma_address = sg_phys(sg) + state->bus_off;
+		sg_dma_len(sg) = sg->length;
+		sg_dma_mark_pci_p2pdma(sg);
+	}
+
+	return state->map;
+}
+
+/**
+ * pci_p2pdma_map_bus_segment - map an sg segment pre determined to
+ *	be mapped with PCI_P2PDMA_MAP_BUS_ADDR
+ * @pg_sg: scatterlist segment with the page to map
+ * @dma_sg: scatterlist segment to assign a dma address to
+ *
+ * This is a helper for iommu dma_map_sg() implementations when the
+ * segment for the dma address differs from the segment containing the
+ * source page.
+ *
+ * pci_p2pdma_map_type() must have already been called on the pg_sg and
+ * returned PCI_P2PDMA_MAP_BUS_ADDR.
+ */
+void pci_p2pdma_map_bus_segment(struct scatterlist *pg_sg,
+				struct scatterlist *dma_sg)
+{
+	struct pci_p2pdma_pagemap *pgmap = to_p2p_pgmap(sg_page(pg_sg)->pgmap);
+
+	dma_sg->dma_address = sg_phys(pg_sg) + pgmap->bus_offset;
+	sg_dma_len(dma_sg) = pg_sg->length;
+	sg_dma_mark_pci_p2pdma(dma_sg);
+}
+
 /**
  * pci_p2pdma_enable_store - parse a configfs/sysfs attribute store
  *		to enable p2pdma
diff --git a/include/linux/pci-p2pdma.h b/include/linux/pci-p2pdma.h
index caac2d023f8f..e5a8d5bc0f51 100644
--- a/include/linux/pci-p2pdma.h
+++ b/include/linux/pci-p2pdma.h
@@ -13,6 +13,12 @@
 
 #include <linux/pci.h>
 
+struct pci_p2pdma_map_state {
+	struct dev_pagemap *pgmap;
+	int map;
+	u64 bus_off;
+};
+
 struct block_device;
 struct scatterlist;
 
@@ -70,6 +76,11 @@ int pci_p2pdma_map_sg_attrs(struct device *dev, struct scatterlist *sg,
 		int nents, enum dma_data_direction dir, unsigned long attrs);
 void pci_p2pdma_unmap_sg_attrs(struct device *dev, struct scatterlist *sg,
 		int nents, enum dma_data_direction dir, unsigned long attrs);
+enum pci_p2pdma_map_type
+pci_p2pdma_map_segment(struct pci_p2pdma_map_state *state, struct device *dev,
+		       struct scatterlist *sg);
+void pci_p2pdma_map_bus_segment(struct scatterlist *pg_sg,
+				struct scatterlist *dma_sg);
 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,
@@ -135,6 +146,16 @@ static inline void pci_p2pdma_unmap_sg_attrs(struct device *dev,
 		unsigned long attrs)
 {
 }
+static inline enum pci_p2pdma_map_type
+pci_p2pdma_map_segment(struct pci_p2pdma_map_state *state, struct device *dev,
+		       struct scatterlist *sg)
+{
+	return PCI_P2PDMA_MAP_NOT_SUPPORTED;
+}
+static inline void pci_p2pdma_map_bus_segment(struct scatterlist *pg_sg,
+					      struct scatterlist *dma_sg)
+{
+}
 static inline int pci_p2pdma_enable_store(const char *page,
 		struct pci_dev **p2p_dev, bool *use_p2pdma)
 {
-- 
2.20.1