[PATCH 08/16] PCI/P2PDMA: Introduce helpers for dma_map_sg implementations

Logan Gunthorpe
2021-04-08T17:01:58Z

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@deltatee.com>
---
drivers/pci/p2pdma.c | 65 ++++++++++++++++++++++++++++++++++++++
include/linux/pci-p2pdma.h | 21 ++++++++++++
2 files changed, 86 insertions(+)

diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
index 38c93f57a941..44ad7664e875 100644
--- a/drivers/pci/p2pdma.c
+++ b/drivers/pci/p2pdma.c
@@ -923,6 +923,71 @@ 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 on the stack 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
+ * @attrs: dma mapping attributes
+ *
+ * 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 1 if the segment was mapped, 0 if the segment should be mapped
+ * directly (or through the IOMMU) and -EREMOTEIO if the segment should not
+ * be mapped at all.
+ */
+int pci_p2pdma_map_segment(struct pci_p2pdma_map_state *state,
+ struct device *dev, struct scatterlist *sg,
+ unsigned long dma_attrs)
+{
+ if (state->pgmap != sg_page(sg)->pgmap) {
+ state->pgmap = sg_page(sg)->pgmap;
+ state->map = pci_p2pdma_map_type(state->pgmap, dev, dma_attrs);
+ state->bus_off = to_p2p_pgmap(state->pgmap)->bus_offset;
+ }
+
+ switch (state->map) {
+ case PCI_P2PDMA_MAP_BUS_ADDR:
+ sg->dma_address = sg_phys(sg) + state->bus_off;
+ sg_dma_len(sg) = sg->length;
+ sg_mark_pci_p2pdma(sg);
+ return 1;
+ case PCI_P2PDMA_MAP_THRU_HOST_BRIDGE:
+ return 0;
+ default:
+ return -EREMOTEIO;
+ }
+}
+
+/**
+ * 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_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 a06072ac3a52..49e7679403cf 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;

@@ -43,6 +49,11 @@ 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);
+int pci_p2pdma_map_segment(struct pci_p2pdma_map_state *state,
+ struct device *dev, struct scatterlist *sg,
+ unsigned long dma_attrs);
+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,
@@ -109,6 +120,16 @@ static inline void pci_p2pdma_unmap_sg_attrs(struct device *dev,
unsigned long attrs)
{
}
+static inline int pci_p2pdma_map_segment(struct pci_p2pdma_map_state *state,
+ struct device *dev, struct scatterlist *sg,
+ unsigned long dma_attrs)
+{
+ return 0;
+}
+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