On 10/30/25 14:05, Boris Brezillon wrote:
The default implementation simply takes care of invalidating/flushing
caches around CPU accesses. It takes care of both the exporter and
the importers, which forces us to overload the default
::[un]map_dma_buf() implementation provided by drm_gem.c to store the
sgt.
v5:
- New patch
Signed-off-by: Boris Brezillon <[email protected]>
---
drivers/gpu/drm/drm_gem_shmem_helper.c | 114 +++++++++++++++++++++++++
include/drm/drm_gem_shmem_helper.h | 10 +++
2 files changed, 124 insertions(+)
diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c
b/drivers/gpu/drm/drm_gem_shmem_helper.c
index dc94a27710e5..e49c75739c20 100644
--- a/drivers/gpu/drm/drm_gem_shmem_helper.c
+++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
@@ -893,6 +893,120 @@ struct drm_gem_object
*drm_gem_shmem_prime_import_no_map(struct drm_device *dev,
}
EXPORT_SYMBOL_GPL(drm_gem_shmem_prime_import_no_map);
+/**
+ * drm_gem_shmem_prime_unmap_dma_buf - Default unmap_dma_buf() for exported
buffers
+ * @attach: attachment
+ * @sgt: SG table to unmap
+ * @dir: type of access done by this attachment
+ *
+ * Default implementation for dma_buf_ops::map_dma_buf(). This is just a
wrapper
+ * around drm_gem_map_dma_buf() that lets us set the dma_buf_attachment::priv
+ * to the sgt so that drm_gem_shmem_prime_{begin,end}_cpu_access() can sync
+ * around CPU accesses.
+ */
+struct sg_table *
+drm_gem_shmem_prime_map_dma_buf(struct dma_buf_attachment *attach,
+ enum dma_data_direction dir)
+{
+ struct sg_table *sgt = drm_gem_map_dma_buf(attach, dir);
+
+ if (!IS_ERR(sgt))
+ attach->priv = sgt;
+
+ return sgt;
+}
+EXPORT_SYMBOL_GPL(drm_gem_shmem_prime_map_dma_buf);
+
+/**
+ * drm_gem_shmem_prime_unmap_dma_buf - Default unmap_dma_buf() for exported
buffers
+ * @attach: attachment
+ * @sgt: SG table to unmap
+ * @dir: type of access done by this attachment
+ *
+ * Default implementation for dma_buf_ops::unmap_dma_buf(). This is just a
wrapper
+ * around drm_gem_unmap_dma_buf() that lets us reset the
dma_buf_attachment::priv
+ * field so that drm_gem_shmem_prime_{begin,end}_cpu_access() don't consider it
+ * as a mapped attachment to sync against.
+ */
+void drm_gem_shmem_prime_unmap_dma_buf(struct dma_buf_attachment *attach,
+ struct sg_table *sgt,
+ enum dma_data_direction dir)
+{
+ attach->priv = NULL;
+ drm_gem_unmap_dma_buf(attach, sgt, dir);
+}
+EXPORT_SYMBOL_GPL(drm_gem_shmem_prime_unmap_dma_buf);
+
+/**
+ * drm_gem_shmem_prime_begin_cpu_access - Default end_cpu_access() for
exported buffers
Sorry nitpick. There is a typo here. Should be 'Default begin_cpu_access()`.
+ * @dma_buf: The exported DMA buffer this acts on
+ * @dir: direction of the access
+ *
+ * Default implementation for dma_buf_ops::begin_cpu_access(). This only takes
care of
+ * cache maintenance.
+ */
+int drm_gem_shmem_prime_begin_cpu_access(struct dma_buf *dma_buf,
+ enum dma_data_direction dir)
+{
+ struct drm_gem_object *obj = dma_buf->priv;
+ struct drm_device *dev = obj->dev;
+ struct drm_gem_shmem_object *shmem = to_drm_gem_shmem_obj(obj);
+ struct dma_buf_attachment *attach;
+
+ dma_resv_lock(obj->resv, NULL);
+ if (shmem->sgt)
+ dma_sync_sgtable_for_cpu(dev->dev, shmem->sgt, dir);
+
+ if (shmem->vaddr)
+ invalidate_kernel_vmap_range(shmem->vaddr, shmem->base.size);
+
+ list_for_each_entry(attach, &dma_buf->attachments, node) {
+ struct sg_table *sgt = attach->priv;
+
+ if (sgt)
+ dma_sync_sgtable_for_cpu(attach->dev, sgt, dir);
+ }
+ dma_resv_unlock(obj->resv);
+
+ return 0;
+}
+EXPORT_SYMBOL_GPL(drm_gem_shmem_prime_begin_cpu_access);
+
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