Hi
Am 16.10.26 um 08:26 schrieb Niranjana Vishwanathapura:
On Thu, Oct 15, 2026 at 09:27:08AM +0200, Thomas Zimmermann wrote:
Hi
Am 14.10.26 um 21:02 schrieb Niranjana Vishwanathapura:
From: Farah Kassabri <[email protected]>
Add drm_gem_prime_self_import() to detect and handle the case where a
PRIME dma-buf being imported was exported by the same DRM device.
When the dma-buf originates from the importing device and uses the
expected dma-buf ops, the helper returns the associated GEM object and
takes an extra reference on it. This allows drivers to bypass the
generic PRIME import path and avoid taking an additional reference on
the dma-buf file.
The helper simplifies self-import handling and avoids duplication of
this pattern across DRM drivers.
v2: Move drm_gem_prime_self_import() to drm_gem.h as a static inline
helper routine
Why even bother submitting this? It is the same series that I already
declined with a few cosmetic changes.
The abstract entry point for importing is
drm_driver.gem_prime_import. The implementation is driver specific.
No need to over abstract. Keeping drm_gem_object_get() separate from
the test is a feature, not a bug BTW.
If you want to improve the status quo, change dma-buf such that prime
works without relying on the vtable and ->priv. I outlined this in my
earlier replies.
Hi Thomas,
As mentioned in other thread, your earlier suggesion of
'__drm_gem_is_exported_dma_buf(dev, ops, dma_buf)' is not fully helpful
as it would require drivers to still take object reference. Besides,
this also depends on 'ops'.
This is a feature. These are two distinct operations. Taking the object
ref is another of those implementation detail where drivers might want
to do something else.
To me the 'dma_buf_ops as export identifer' seems to be well accepted
idiom, though we may say it shouldn't be in stricter sense.
But if we were not to relay on vtable and ->priv, then it looks like
the best alternative will be to have DRM subsystem maintain a list of
exported dma-buf objects per drm device. Then during import, parse this
list to determine if the import is self-import or not.
I am not sure if it is worth to add this list just for this simple helper
routine. If using dma_buf ops is no go, then yah, let us drop this
series,
keep current code and may be look into this alternative later through
an RFC.
As I mention before, the abstraction is drm_driver.gem_prime_import.
Anything behind that is driver-specific. A real improvement should
provide a driver-generic implementation of gem_prime_import. This needs
changes to dma_buf and to the prime helpers. OTOH gem_prime_import is
already fairly abstract. There are no low-hanging fruits here IMHO.
Best regards
Thomas
Thanks,
Niranjana
Best regards
Thomas
Signed-off-by: Farah Kassabri <[email protected]>
Signed-off-by: Niranjana Vishwanathapura
<[email protected]>
Reviewed-by: Matthew Brost <[email protected]>
---
drivers/gpu/drm/drm_prime.c | 10 ++-------
include/drm/drm_gem.h | 42 +++++++++++++++++++++++++++++++++++++
2 files changed, 44 insertions(+), 8 deletions(-)
diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
index 9b44c78cd77f..7a15c29052eb 100644
--- a/drivers/gpu/drm/drm_prime.c
+++ b/drivers/gpu/drm/drm_prime.c
@@ -974,15 +974,9 @@ struct drm_gem_object
*drm_gem_prime_import_dev(struct drm_device *dev,
struct drm_gem_object *obj;
int ret;
- if (drm_gem_is_prime_exported_dma_buf(dev, dma_buf)) {
- /*
- * Importing dmabuf exported from our own gem increases
- * refcount on gem itself instead of f_count of dmabuf.
- */
- obj = dma_buf->priv;
- drm_gem_object_get(obj);
+ obj = drm_gem_prime_self_import(dev, dma_buf,
&drm_gem_prime_dmabuf_ops);
+ if (obj)
return obj;
- }
if (!dev->driver->gem_prime_import_sg_table)
return ERR_PTR(-EINVAL);
diff --git a/include/drm/drm_gem.h b/include/drm/drm_gem.h
index 885244e375d3..238ec08f0d81 100644
--- a/include/drm/drm_gem.h
+++ b/include/drm/drm_gem.h
@@ -646,6 +646,48 @@ static inline bool drm_gem_is_imported(const
struct drm_gem_object *obj)
return !!obj->import_attach;
}
+/**
+ * drm_gem_prime_self_import - Attempt to import a dma-buf exported
by this DRM device
+ * @dev: DRM device performing the import
+ * @dma_buf: dma-buf to import
+ * @expected_ops: dma-buf ops used by this driver
+ *
+ * If @dma_buf was exported by this DRM device using @expected_ops,
return the
+ * corresponding GEM object and take an extra reference on it. In
this case,
+ * the import avoids taking a reference on the dma-buf file and
instead bumps
+ * the GEM object's refcount directly.
+ *
+ * Comparing @dma_buf->ops against @expected_ops is plumbing:
dma-buf has no
+ * first-class exporter identifier, so the ops pointer is used as a
stand-in to
+ * recognise a buffer this driver exported. A dedicated exporter
identity would
+ * let this be done without reaching into @dma_buf->ops.
+ *
+ * Returns:
+ * A referenced GEM object on success, or %NULL if the dma-buf was
not exported
+ * by this device or does not match @expected_ops.
+ */
+static inline struct drm_gem_object *
+drm_gem_prime_self_import(struct drm_device *dev, struct dma_buf
*dma_buf,
+ const struct dma_buf_ops *expected_ops)
+{
+ struct drm_gem_object *obj;
+
+ if (dma_buf->ops != expected_ops)
+ return NULL;
+
+ obj = dma_buf->priv;
+ if (obj->dev != dev)
+ return NULL;
+
+ /*
+ * Importing dmabuf exported from the driver's own gem increases
+ * refcount on gem itself instead of f_count of dmabuf.
+ */
+ drm_gem_object_get(obj);
+
+ return obj;
+}
+
#ifdef CONFIG_LOCKDEP
#define drm_gem_gpuva_assert_lock_held(gpuvm, obj) \
lockdep_assert(drm_gpuvm_immediate_mode(gpuvm) ? \
--
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstr. 146, 90461 Nürnberg, Germany, www.suse.com
GF: Stefan Gaiser, Jochen Jaser, Abhinav Puri, (HRB 36809, AG Nürnberg)
--
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstr. 146, 90461 Nürnberg, Germany, www.suse.com
GF: Stefan Gaiser, Jochen Jaser, Abhinav Puri, (HRB 36809, AG Nürnberg)
