[PATCH RFC 02/26] dma-buf: Add the SGT DMA mapping type

[Jason Gunthorpe <jgg@nvidia.com>]

The SGT (Scatter Gather Table) DMA mapping type represents the existing
sg_table/scatterlist based DMA mapping. It provides a sg_table based
map/unmap interface that exactly matches how things work today.

dma_buf_sgt_exp_compat_match will be used in the next patch to
transparently wrap an unaware exporter with a mapping type.

The SGT type handles the allow_peer2peer flag directly through matching
logic. The importer indicates if it is willing to accept peer2peer and the
exporter indicates if it requires peer2peer. A required peer2peer exporter
will not match to an importer that does not accept peer2peer.

Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
---
 drivers/dma-buf/dma-buf-mapping.c |  95 ++++++++++++++++++++++++++++
 include/linux/dma-buf-mapping.h   | 101 ++++++++++++++++++++++++++++++
 include/linux/dma-buf.h           |  18 +++++-
 3 files changed, 213 insertions(+), 1 deletion(-)

diff --git a/drivers/dma-buf/dma-buf-mapping.c b/drivers/dma-buf/dma-buf-mapping.c
index 459c204cabb803..02f5cf8b3def40 100644
--- a/drivers/dma-buf/dma-buf-mapping.c
+++ b/drivers/dma-buf/dma-buf-mapping.c
@@ -6,6 +6,7 @@
 #include <linux/dma-buf-mapping.h>
 #include <linux/dma-resv.h>
 #include <linux/dma-buf.h>
+#include <linux/seq_file.h>
 
 static struct scatterlist *fill_sg_entry(struct scatterlist *sgl, size_t length,
 					 dma_addr_t addr)
@@ -292,3 +293,97 @@ int dma_buf_match_mapping(struct dma_buf_match_args *args,
 	return -EINVAL;
 }
 EXPORT_SYMBOL_NS_GPL(dma_buf_match_mapping, "DMA_BUF");
+
+static int dma_buf_sgt_match(struct dma_buf *dmabuf,
+			     const struct dma_buf_mapping_match *exp,
+			     const struct dma_buf_mapping_match *imp)
+{
+	switch (exp->sgt_data.exporter_requires_p2p) {
+	case DMA_SGT_NO_P2P:
+		return 0;
+	case DMA_SGT_EXPORTER_REQUIRES_P2P_DISTANCE:
+		if (WARN_ON(!exp->sgt_data.exporting_p2p_device) ||
+		    imp->sgt_data.importer_accepts_p2p !=
+			    DMA_SGT_IMPORTER_ACCEPTS_P2P)
+			return -EOPNOTSUPP;
+		if (pci_p2pdma_distance(exp->sgt_data.exporting_p2p_device,
+					imp->sgt_data.importing_dma_device,
+					true) < 0)
+			return -EOPNOTSUPP;
+		return 0;
+	}
+	return 0;
+}
+
+static inline void
+dma_buf_sgt_finish_match(struct dma_buf_match_args *args,
+			 const struct dma_buf_mapping_match *exp,
+			 const struct dma_buf_mapping_match *imp)
+{
+	struct dma_buf_attachment *attach = args->attach;
+
+	attach->map_type = (struct dma_buf_mapping_match) {
+		.type = &dma_buf_mapping_sgt_type,
+		.exp_ops = exp->exp_ops,
+		.sgt_data = {
+			.importing_dma_device = imp->sgt_data.importing_dma_device,
+			/* exporting_p2p_device is left opaque */
+			.importer_accepts_p2p = imp->sgt_data.importer_accepts_p2p,
+			.exporter_requires_p2p = exp->sgt_data.exporter_requires_p2p,
+		},
+	};
+
+	/*
+	 * Setup the SGT type variables stored in attach because importers and
+	 * exporters that do not natively use mappings expect them to be there.
+	 * When converting to use mappings users should use the match versions
+	 * of these instead.
+	 */
+	attach->dev = imp->sgt_data.importing_dma_device;
+	attach->peer2peer = attach->map_type.sgt_data.importer_accepts_p2p ==
+			    DMA_SGT_IMPORTER_ACCEPTS_P2P;
+}
+
+static void dma_buf_sgt_debugfs_dump(struct seq_file *s,
+				     struct dma_buf_attachment *attach)
+{
+	seq_printf(s, " %s", dev_name(dma_buf_sgt_dma_device(attach)));
+}
+
+struct dma_buf_mapping_type dma_buf_mapping_sgt_type = {
+	.name = "DMA Mapped Scatter Gather Table",
+	.match = dma_buf_sgt_match,
+	.finish_match = dma_buf_sgt_finish_match,
+	.debugfs_dump = dma_buf_sgt_debugfs_dump,
+};
+EXPORT_SYMBOL_NS_GPL(dma_buf_mapping_sgt_type, "DMA_BUF");
+
+static struct sg_table *
+dma_buf_sgt_compat_map_dma_buf(struct dma_buf_attachment *attach,
+			       enum dma_data_direction dir)
+{
+	return attach->dmabuf->ops->map_dma_buf(attach, dir);
+}
+
+static void dma_buf_sgt_compat_unmap_dma_buf(struct dma_buf_attachment *attach,
+					     struct sg_table *sgt,
+					     enum dma_data_direction dir)
+{
+	attach->dmabuf->ops->unmap_dma_buf(attach, sgt, dir);
+}
+
+/* Route the classic map/unmap ops through the exp ops for old importers */
+static const struct dma_buf_mapping_sgt_exp_ops dma_buf_sgt_compat_exp_ops = {
+	.map_dma_buf = dma_buf_sgt_compat_map_dma_buf,
+	.unmap_dma_buf = dma_buf_sgt_compat_unmap_dma_buf,
+};
+
+/*
+ * This mapping type is used for unaware exporters that do not support
+ * match_mapping(). It wraps the dma_buf ops for SGT mappings into a mapping
+ * type so aware importers can transparently work with unaware exporters. This
+ * does not require p2p because old exporters will check it through the
+ * attach->peer2peer mechanism.
+ */
+const struct dma_buf_mapping_match dma_buf_sgt_exp_compat_match =
+	DMA_BUF_EMAPPING_SGT(&dma_buf_sgt_compat_exp_ops);
diff --git a/include/linux/dma-buf-mapping.h b/include/linux/dma-buf-mapping.h
index 080ccbf3a3f8b8..360a7fe0b098be 100644
--- a/include/linux/dma-buf-mapping.h
+++ b/include/linux/dma-buf-mapping.h
@@ -12,6 +12,12 @@ struct dma_buf;
 struct dma_buf_attachment;
 struct dma_buf_mapping_exp_ops;
 
+enum dma_sgt_requires_p2p {
+	DMA_SGT_NO_P2P = 0,
+	DMA_SGT_EXPORTER_REQUIRES_P2P_DISTANCE,
+	DMA_SGT_IMPORTER_ACCEPTS_P2P,
+};
+
 /* Type tag for all mapping operations */
 struct dma_buf_mapping_exp_ops {};
 
@@ -90,4 +96,99 @@ int dma_buf_match_mapping(struct dma_buf_match_args *args,
 			  const struct dma_buf_mapping_match *exp_mappings,
 			  size_t exp_len);
 
+/*
+ * DMA Mapped Scatterlist Type
+ *
+ * When this type is matched the map/unmap functions are:
+ *
+ *  dma_buf_map_attachment()
+ *  dma_buf_unmap_attachment()
+ *
+ * The struct sg_table returned by those functions has only the DMA portions
+ * available. The caller must not try to use the struct page * information.
+ *
+ * importing_dma_device is passed to the DMA API to provide the dma_addr_t's.
+ */
+extern struct dma_buf_mapping_type dma_buf_mapping_sgt_type;
+
+struct dma_buf_mapping_sgt_exp_ops {
+	struct dma_buf_mapping_exp_ops ops;
+	struct sg_table *(*map_dma_buf)(struct dma_buf_attachment *attach,
+					enum dma_data_direction dir);
+	void (*unmap_dma_buf)(struct dma_buf_attachment *attach,
+			      struct sg_table *sgt,
+			      enum dma_data_direction dir);
+};
+
+/**
+ * dma_buf_sgt_dma_device - Return the device to use for DMA mapping
+ * @attach: sgt mapping type attachment
+ *
+ * Called by the exporter to get the struct device to pass to the DMA API
+ * during map and unmap callbacks.
+ */
+static inline struct device *
+dma_buf_sgt_dma_device(struct dma_buf_attachment *attach)
+{
+	if (attach->map_type.type != &dma_buf_mapping_sgt_type)
+		return NULL;
+	return attach->map_type.sgt_data.importing_dma_device;
+}
+
+/**
+ * dma_buf_sgt_p2p_allowed - True if MMIO memory can be used peer to peer
+ * @attach: sgt mapping type attachment
+ *
+ * Should be called by exporters, returns true if the exporter's
+ * DMA_SGT_EXPORTER_REQUIRES_P2P_DISTANCE was matched.
+ */
+static inline bool dma_buf_sgt_p2p_allowed(struct dma_buf_attachment *attach)
+{
+	if (attach->map_type.type != &dma_buf_mapping_sgt_type)
+		return false;
+	return attach->map_type.sgt_data.exporter_requires_p2p ==
+	       DMA_SGT_EXPORTER_REQUIRES_P2P_DISTANCE;
+}
+
+static inline const struct dma_buf_mapping_sgt_exp_ops *
+dma_buf_get_sgt_ops(struct dma_buf_attachment *attach)
+{
+	if (attach->map_type.type != &dma_buf_mapping_sgt_type)
+		return NULL;
+	return container_of(attach->map_type.exp_ops,
+			    struct dma_buf_mapping_sgt_exp_ops, ops);
+}
+
+static inline struct dma_buf_mapping_match
+DMA_BUF_IMAPPING_SGT(struct device *importing_dma_device,
+		     enum dma_sgt_requires_p2p importer_accepts_p2p)
+{
+	return (struct dma_buf_mapping_match){
+		.type = &dma_buf_mapping_sgt_type,
+		.sgt_data = { .importing_dma_device = importing_dma_device,
+			      .importer_accepts_p2p = importer_accepts_p2p },
+	};
+}
+#define DMA_BUF_EMAPPING_SGT(_exp_ops)                                      \
+	((struct dma_buf_mapping_match){ .type = &dma_buf_mapping_sgt_type, \
+					 .exp_ops = &((_exp_ops)->ops) })
+
+/*
+ * Only matches if the importing device is P2P capable and the P2P subsystem
+ * says P2P is possible from p2p_device.
+ */
+static inline struct dma_buf_mapping_match
+DMA_BUF_EMAPPING_SGT_P2P(const struct dma_buf_mapping_sgt_exp_ops *exp_ops,
+			 struct pci_dev *p2p_device)
+{
+	struct dma_buf_mapping_match match = DMA_BUF_EMAPPING_SGT(exp_ops);
+
+	match.sgt_data.exporter_requires_p2p =
+		DMA_SGT_EXPORTER_REQUIRES_P2P_DISTANCE;
+	match.sgt_data.exporting_p2p_device = p2p_device;
+	return match;
+}
+
+extern const struct dma_buf_mapping_match dma_buf_sgt_exp_compat_match;
+
 #endif
diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
index a2b01b13026810..3bcd1d6d150188 100644
--- a/include/linux/dma-buf.h
+++ b/include/linux/dma-buf.h
@@ -30,6 +30,7 @@ struct dma_buf_attachment;
 struct dma_buf_mapping_type;
 struct dma_buf_mapping_exp_ops;
 
+
 /*
  * Match items are generated by the importer using the DMA_BUF_IMAPPING_*() and
  * the exporter using the DMA_BUF_EMAPPING_*() functions. Each mapping type
@@ -39,7 +40,22 @@ struct dma_buf_mapping_match {
 	const struct dma_buf_mapping_type *type;
 	const struct dma_buf_mapping_exp_ops *exp_ops;
 	union {
-		/* Each mapping_type has unique match parameters here */
+		/* For dma_buf_mapping_sgt_type */
+		struct {
+			struct device *importing_dma_device;
+			/* Only used if DMA_SGT_EXPORTER_REQUIRES_P2P_DISTANCE */
+			struct pci_dev *exporting_p2p_device;
+			/*
+			 * These p2p flags are used to support the hard coded
+			 * mechanism for p2p. If an exporting device knows it
+			 * will put MMIO into the sgt then it should set
+			 * exporter_requires_p2p. Importers should set
+			 * importer_accepts_p2p unless it is known that the
+			 * importing HW never supports P2P because of HW issues.
+			 */
+			u8 importer_accepts_p2p;
+			u8 exporter_requires_p2p;
+		} sgt_data;
 	};
 };
 
-- 
2.43.0