[PATCH 06/26] dma-buf: Add match set queries for exporter placement decisions

[Alistair Popple <apopple@nvidia.com>]

Exporters deciding placement in their pin path walk every attachment
to determine whether it can take P2P. With selection deferred to pin or
map an unmapped attachment only holds the exporter's default. Therefore
determining what is possible requires walking attachments.

Add dma_buf_attach_accepts() and dma_buf_attach_accepts_sgt_p2p() to
walk the match set and determine if an attachment is possible with P2P.
A future series will convert P2P into a distinct match type.

Assisted-by: LLM
Signed-off-by: Alistair Popple <apopple@nvidia.com>
---
 include/linux/dma-buf-mapping.h | 46 +++++++++++++++++++++++++++++++++
 1 file changed, 46 insertions(+)

diff --git a/include/linux/dma-buf-mapping.h b/include/linux/dma-buf-mapping.h
index c04fac71726a..494bc29910f4 100644
--- a/include/linux/dma-buf-mapping.h
+++ b/include/linux/dma-buf-mapping.h
@@ -102,6 +102,26 @@ int dma_buf_match_mapping(struct dma_buf_match_args *args,
  */
 int dma_buf_mapping_select(struct dma_buf_attachment *attach);
 
+/**
+ * dma_buf_attach_accepts - Is @type in the attachment's match set
+ * @attach: the attachment
+ * @type: a mapping type
+ *
+ * Called by exporters deciding placement in pin or select_mapping to determine
+ * whether the importer could be served with @type.
+ */
+static inline bool
+dma_buf_attach_accepts(const struct dma_buf_attachment *attach,
+		       const struct dma_buf_mapping_type *type)
+{
+	unsigned int i;
+
+	for (i = 0; i < attach->nr_matches; i++)
+		if (attach->matches[i].type == type)
+			return true;
+	return false;
+}
+
 /*
  * DMA Mapped Scatterlist Type
  *
@@ -147,6 +167,10 @@ dma_buf_sgt_dma_device(struct dma_buf_attachment *attach)
  *
  * Should be called by exporters, returns true if the exporter's
  * DMA_SGT_EXPORTER_REQUIRES_P2P_DISTANCE was matched.
+ *
+ * Reflects the current selection, so is only meaningful inside the
+ * exporter's pin and map callbacks. For attachments which may be unmapped use
+ * dma_buf_attach_accepts_sgt_p2p().
  */
 static inline bool dma_buf_sgt_p2p_allowed(struct dma_buf_attachment *attach)
 {
@@ -156,6 +180,28 @@ static inline bool dma_buf_sgt_p2p_allowed(struct dma_buf_attachment *attach)
 	       DMA_SGT_EXPORTER_REQUIRES_P2P_DISTANCE;
 }
 
+/**
+ * dma_buf_attach_accepts_sgt_p2p - Could this attachment take a P2P SGT?
+ * @attach: any attachment
+ *
+ * Like dma_buf_sgt_p2p_allowed() but valid for attachments that are not mapped.
+ * Instead determines if p2p is part of the current possible match set rather
+ * than the current selection. Called by exporters walking all attachments in
+ * their pin path.
+ */
+static inline bool
+dma_buf_attach_accepts_sgt_p2p(const struct dma_buf_attachment *attach)
+{
+	unsigned int i;
+
+	for (i = 0; i < attach->nr_matches; i++)
+		if (attach->matches[i].type == &dma_buf_mapping_sgt_type &&
+		    attach->matches[i].sgt_data.exporter_requires_p2p ==
+			    DMA_SGT_EXPORTER_REQUIRES_P2P_DISTANCE)
+			return true;
+	return false;
+}
+
 static inline const struct dma_buf_mapping_sgt_exp_ops *
 dma_buf_get_sgt_ops(struct dma_buf_attachment *attach)
 {
-- 
2.54.0