[PATCH RFC 05/26] dma-buf: Allow single exporter drivers to avoid the match_mapping function

[Jason Gunthorpe <jgg@nvidia.com>]

Introduce single_exporter_match into the dma_buf_ops so that single
exporter drivers can simply set it using a static initializer to use the
mapping type APIs. Provide a helper macro DMA_BUF_SIMPLE_SGT_EXP_MATCH()
that generates the initializer for simple drivers that don't use P2P.

More complex exporters, especially those with P2P, need to implement the
match_mapping call back to extract things like their DMA struct device
from the dma_buf in order to do the P2P calculations.

Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
---
 drivers/dma-buf/dma-buf.c       | 14 +++++++++++---
 include/linux/dma-buf-mapping.h | 15 +++++++++++++++
 include/linux/dma-buf.h         |  9 +++++++++
 3 files changed, 35 insertions(+), 3 deletions(-)

diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
index 4211ae2b462bdd..ac755f358dc7b3 100644
--- a/drivers/dma-buf/dma-buf.c
+++ b/drivers/dma-buf/dma-buf.c
@@ -693,10 +693,14 @@ struct dma_buf *dma_buf_export(const struct dma_buf_export_info *exp_info)
 		    || !exp_info->ops->release))
 		return ERR_PTR(-EINVAL);
 
-	if (exp_info->ops->match_mapping) {
+	if (exp_info->ops->match_mapping ||
+	    exp_info->ops->single_exporter_match) {
 		if (WARN_ON(exp_info->ops->map_dma_buf ||
 			    exp_info->ops->unmap_dma_buf))
 			return ERR_PTR(-EINVAL);
+		if (WARN_ON(exp_info->ops->match_mapping &&
+			    exp_info->ops->single_exporter_match))
+			return ERR_PTR(-EINVAL);
 	} else {
 		if (WARN_ON(!exp_info->ops->map_dma_buf ||
 			    !exp_info->ops->unmap_dma_buf))
@@ -977,8 +981,12 @@ struct dma_buf_attachment *dma_buf_mapping_attach(
 		if (ret)
 			goto err_attach;
 	} else {
-		ret = dma_buf_match_mapping(&match_args,
-					    &dma_buf_sgt_exp_compat_match, 1);
+		const struct dma_buf_mapping_match *exp_match =
+			dmabuf->ops->single_exporter_match;
+
+		if (!exp_match)
+			exp_match = &dma_buf_sgt_exp_compat_match;
+		ret = dma_buf_match_mapping(&match_args, exp_match, 1);
 		if (ret)
 			goto err_attach;
 	}
diff --git a/include/linux/dma-buf-mapping.h b/include/linux/dma-buf-mapping.h
index 360a7fe0b098be..c11e32ef2a684f 100644
--- a/include/linux/dma-buf-mapping.h
+++ b/include/linux/dma-buf-mapping.h
@@ -191,4 +191,19 @@ DMA_BUF_EMAPPING_SGT_P2P(const struct dma_buf_mapping_sgt_exp_ops *exp_ops,
 
 extern const struct dma_buf_mapping_match dma_buf_sgt_exp_compat_match;
 
+/*
+ * dma_buf_ops initializer helper for simple drivers that use a single
+ * SGT map/unmap operation without P2P.
+ */
+#define DMA_BUF_SIMPLE_SGT_EXP_MATCH(_map, _unmap)                       \
+	.single_exporter_match = &((const struct dma_buf_mapping_match){ \
+		.type = &dma_buf_mapping_sgt_type,                       \
+		.exp_ops = &((const struct dma_buf_mapping_sgt_exp_ops){ \
+			.map_dma_buf = _map,                             \
+			.unmap_dma_buf = _unmap,                         \
+		}.ops),                                                  \
+		.sgt_data = {                                            \
+			.exporter_requires_p2p = DMA_SGT_NO_P2P,         \
+		} })
+
 #endif
diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
index 14d556bb022862..a8cfbbafbe31fe 100644
--- a/include/linux/dma-buf.h
+++ b/include/linux/dma-buf.h
@@ -317,6 +317,15 @@ struct dma_buf_ops {
 	 * struct dma_buf_mapping_match[] and call dma_buf_match_mapping().
 	 */
 	int (*match_mapping)(struct dma_buf_match_args *args);
+
+	/**
+	 * @single_exporter_match:
+	 *
+	 * Should only be set by the DMA_BUF_SIMPLE_*_EXP_MATCH() helper macros.
+	 * Exactly one of @match_mapping or @single_exporter_match must be
+	 * provided.
+	 */
+	const struct dma_buf_mapping_match *single_exporter_match;
 };
 
 /**
-- 
2.43.0