Hi
Am 27.11.25 um 09:34 schrieb Thomas Zimmermann:
Hi
Am 26.11.25 um 13:44 schrieb Boris Brezillon:
drm_gem_is_prime_exported_dma_buf() checks the dma_buf->ops against
drm_gem_prime_dmabuf_ops, which makes it impossible to use if the
driver implements custom dma_buf_ops. Instead of duplicating a bunch
of helpers to work around it, let's provide a way for drivers to
expose their custom dma_buf_ops so the core prime helpers can rely on
that instead of hardcoding &drm_gem_prime_dmabuf_ops.
This can't go in as-is. I've spent an awful amount of patches on
removing buffer callbacks from struct drm_driver. Let's please not go
back to that.
v5:
- New patch
v6:
- Pass custom dma_buf_ops directly instead of through a getter
Signed-off-by: Boris Brezillon <[email protected]>
---
drivers/gpu/drm/drm_prime.c | 10 ++++++++--
include/drm/drm_drv.h | 8 ++++++++
2 files changed, 16 insertions(+), 2 deletions(-)
diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
index 21809a82187b..86fd95f0c105 100644
--- a/drivers/gpu/drm/drm_prime.c
+++ b/drivers/gpu/drm/drm_prime.c
@@ -904,6 +904,12 @@ unsigned long
drm_prime_get_contiguous_size(struct sg_table *sgt)
}
EXPORT_SYMBOL(drm_prime_get_contiguous_size);
+static const struct dma_buf_ops *
+drm_gem_prime_get_dma_buf_ops(struct drm_device *dev)
+{
+ return dev->driver->dma_buf_ops ?: &drm_gem_prime_dmabuf_ops;
+}
+
/**
* drm_gem_prime_export - helper library implementation of the
export callback
* @obj: GEM object to export
@@ -920,7 +926,7 @@ struct dma_buf *drm_gem_prime_export(struct
drm_gem_object *obj,
struct dma_buf_export_info exp_info = {
.exp_name = KBUILD_MODNAME, /* white lie for debug */
.owner = dev->driver->fops->owner,
- .ops = &drm_gem_prime_dmabuf_ops,
+ .ops = drm_gem_prime_get_dma_buf_ops(dev),
Rather provide a new function drm_gem_prime_export_with_ops() that
takes an additional dma_ops instance. The current
drm_gem_prime_export() would call it with &drm_gem_prime_dmabuf_ops.
If this really does not work, you could add a pointer to dma_buf_ops
to drm_gem_object_funcs and fetch that from drm_gem_prime_export(). We
already vm_ops there.
Other drivers, such as amdgpu, would also benefit from such a change
.size = obj->size,
.flags = flags,
.priv = obj,
@@ -947,7 +953,7 @@ bool drm_gem_is_prime_exported_dma_buf(struct
drm_device *dev,
{
struct drm_gem_object *obj = dma_buf->priv;
- return (dma_buf->ops == &drm_gem_prime_dmabuf_ops) &&
(obj->dev == dev);
+ return dma_buf->ops == drm_gem_prime_get_dma_buf_ops(dev) &&
obj->dev == dev;
On a second thought, we probably cannot be sure that dma_buf->priv
really is a GEM object until we tested the ops field. :/ IIRC that's
why the ops test goes first and the test for obj->dev goes second. So
neither solution works.
Best regards
Thomas
This is a bit more complicated and the test has been a pain point
before. For this case, I think we should add a GEM callback for this
struct drm_gem_object_funcs {
bool (*exported_by)(struct drm_gem_object *obj, struct drm_device
*dev)
}
next to the existing export callback.
And drm_gem_is_prime_exported_dma_buf would then do
{
if (obj->funcs->exported_by)
return obj->funcs-<exported_by(obj, dev)
return /* what we currently test */
}
IIRC amdgpu would again benefit from this.
These changes will isolate dma_buf handling near GEM code, keep
drm_driver clean, and even allow for a driver to have different
implementations of dma_buf_ops.
Best regards
Thomas
}
EXPORT_SYMBOL(drm_gem_is_prime_exported_dma_buf);
diff --git a/include/drm/drm_drv.h b/include/drm/drm_drv.h
index 42fc085f986d..1c6dae60d523 100644
--- a/include/drm/drm_drv.h
+++ b/include/drm/drm_drv.h
@@ -431,6 +431,14 @@ struct drm_driver {
* some examples.
*/
const struct file_operations *fops;
+
+ /**
+ * @dma_buf_ops:
+ *
+ * dma_buf_ops to use for buffers exported by this driver. When
NULL,
+ * the drm_prime logic defaults to &drm_gem_prime_dmabuf_ops.
+ */
+ const struct dma_buf_ops *dma_buf_ops;
};
void *__devm_drm_dev_alloc(struct device *parent,
--
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstr. 146, 90461 Nürnberg, Germany, www.suse.com
GF: Jochen Jaser, Andrew McDonald, Werner Knoblich, (HRB 36809, AG Nürnberg)
