[PATCH v7 04/21] PCI/P2PDMA: Introduce helpers for dma_map_sg implementations

Logan Gunthorpe
2022-06-15T16:13:19Z

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.

Prototypes for these helpers are added to dma-map-ops.h as they are only
useful to dma map implementations and don't need to pollute the public
pci-p2pdma header.

Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>
---
drivers/pci/p2pdma.c | 59 +++++++++++++++++++++++++++++++++++++
include/linux/dma-map-ops.h | 21 +++++++++++++
2 files changed, 80 insertions(+)

diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
index 10b1d5c2b5de..2fc0f4750a2e 100644
--- a/drivers/pci/p2pdma.c
+++ b/drivers/pci/p2pdma.c
@@ -951,6 +951,65 @@ 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_bus_address(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_bus_address(dma_sg);
+}
+
/**
* pci_p2pdma_enable_store - parse a configfs/sysfs attribute store
* to enable p2pdma
diff --git a/include/linux/dma-map-ops.h b/include/linux/dma-map-ops.h
index d693a0e33bac..752f91e5eb5d 100644
--- a/include/linux/dma-map-ops.h
+++ b/include/linux/dma-map-ops.h
@@ -413,15 +413,36 @@ enum pci_p2pdma_map_type {
PCI_P2PDMA_MAP_THRU_HOST_BRIDGE,
};

+struct pci_p2pdma_map_state {
+ struct dev_pagemap *pgmap;
+ int map;
+ u64 bus_off;
+};
+
#ifdef CONFIG_PCI_P2PDMA
enum pci_p2pdma_map_type pci_p2pdma_map_type(struct dev_pagemap *pgmap,
struct device *dev);
+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);
#else /* CONFIG_PCI_P2PDMA */
static inline enum pci_p2pdma_map_type
pci_p2pdma_map_type(struct dev_pagemap *pgmap, struct device *dev)
{
return PCI_P2PDMA_MAP_NOT_SUPPORTED;
}
+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)
+{
+}
#endif /* CONFIG_PCI_P2PDMA */

#endif /* _LINUX_DMA_MAP_OPS_H */
--
2.30.2