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

Jason Gunthorpe
2026-02-18T00:12:04Z

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