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drm/prime: remove drm_prime_lookup_buf_by_handle

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This was added by Sima +10 years ago as a solution to avoid exporting
multiple dma-bufs for the same GEM object. I tried to remove it before,
but wasn't 100% sure about all the side effects.

Now Thomas recent modified drm_gem_prime_handle_to_dmabuf() which makes
it obvious that this is a superflous step. We try to look up the DMA-buf
by handle handle and if that fails for some reason (must likely because
the handle is a duplicate) the code just use the DMA-buf from the GEM
object.

Just using the DMA-buf from the GEM object in the first place has the
same effect as far as I can see.

Some more history from Sima:

In d0b2c5334f ("drm/prime: Always add exported buffers to the handle
cache") I added this additional lookup. It wasn't part of the bugfix,
but back then the handle list was just a linked list and you could do
lookups in either direction. And I guess I felt like doing a quick lookup
before we grab the next lock makes sense. Premature optimization, I'm
confessing to the crime guilty as charged :-/

Then Chris Wilson in 077675c1e8 ("drm: Convert prime dma-buf <-> handle
to rbtree") and added 2 rb trees to support both directions. At that point
that handle2buf lookup really didn't make much sense anymore, but we just
kept it and it's been in the tree confusing people ever since.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Simona Vetter <simona.vetter@ffwll.ch>
Link: https://lore.kernel.org/r/20250604113234.2520-1-christian.koenig@amd.com
This commit is contained in:
Christian König 2025-06-04 13:00:38 +02:00
parent c5b4393c54
commit c2aa5603af
3 changed files with 10 additions and 49 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
drivers/gpu/drm/drm_gem.c
View File

@ -282,7 +282,7 @@ drm_gem_object_release_handle(int id, void *ptr, void *data)
if (obj->funcs->close)
obj->funcs->close(obj, file_priv);
drm_prime_remove_buf_handle(&file_priv->prime, id);
drm_prime_remove_buf_handle(&file_priv->prime, obj->dma_buf, id);
drm_vma_node_revoke(&obj->vma_node, file_priv);
drm_gem_object_handle_put_unlocked(obj);

1
drivers/gpu/drm/drm_internal.h
View File

@ -86,6 +86,7 @@ int drm_prime_fd_to_handle_ioctl(struct drm_device *dev, void *data,
void drm_prime_init_file_private(struct drm_prime_file_private *prime_fpriv);
void drm_prime_destroy_file_private(struct drm_prime_file_private *prime_fpriv);
void drm_prime_remove_buf_handle(struct drm_prime_file_private *prime_fpriv,
struct dma_buf *dma_buf,
uint32_t handle);
/* drm_managed.c */

56
drivers/gpu/drm/drm_prime.c
View File

@ -90,7 +90,6 @@ struct drm_prime_member {
uint32_t handle;
struct rb_node dmabuf_rb;
struct rb_node handle_rb;
};
static int drm_prime_add_buf_handle(struct drm_prime_file_private *prime_fpriv,
@ -122,45 +121,9 @@ static int drm_prime_add_buf_handle(struct drm_prime_file_private *prime_fpriv,
rb_link_node(&member->dmabuf_rb, rb, p);
rb_insert_color(&member->dmabuf_rb, &prime_fpriv->dmabufs);
rb = NULL;
p = &prime_fpriv->handles.rb_node;
while (*p) {
struct drm_prime_member *pos;
rb = *p;
pos = rb_entry(rb, struct drm_prime_member, handle_rb);
if (handle > pos->handle)
p = &rb->rb_right;
else
p = &rb->rb_left;
}
rb_link_node(&member->handle_rb, rb, p);
rb_insert_color(&member->handle_rb, &prime_fpriv->handles);
return 0;
}
static struct dma_buf *drm_prime_lookup_buf_by_handle(struct drm_prime_file_private *prime_fpriv,
uint32_t handle)
{
struct rb_node *rb;
rb = prime_fpriv->handles.rb_node;
while (rb) {
struct drm_prime_member *member;
member = rb_entry(rb, struct drm_prime_member, handle_rb);
if (member->handle == handle)
return member->dma_buf;
else if (member->handle < handle)
rb = rb->rb_right;
else
rb = rb->rb_left;
}
return NULL;
}
static int drm_prime_lookup_buf_handle(struct drm_prime_file_private *prime_fpriv,
struct dma_buf *dma_buf,
uint32_t *handle)
@ -186,25 +149,28 @@ static int drm_prime_lookup_buf_handle(struct drm_prime_file_private *prime_fpri
}
void drm_prime_remove_buf_handle(struct drm_prime_file_private *prime_fpriv,
struct dma_buf *dma_buf,
uint32_t handle)
{
struct rb_node *rb;
if (!dma_buf)
return;
mutex_lock(&prime_fpriv->lock);
rb = prime_fpriv->handles.rb_node;
rb = prime_fpriv->dmabufs.rb_node;
while (rb) {
struct drm_prime_member *member;
member = rb_entry(rb, struct drm_prime_member, handle_rb);
if (member->handle == handle) {
rb_erase(&member->handle_rb, &prime_fpriv->handles);
member = rb_entry(rb, struct drm_prime_member, dmabuf_rb);
if (member->dma_buf == dma_buf && member->handle == handle) {
rb_erase(&member->dmabuf_rb, &prime_fpriv->dmabufs);
dma_buf_put(member->dma_buf);
kfree(member);
break;
} else if (member->handle < handle) {
} else if (member->dma_buf < dma_buf) {
rb = rb->rb_right;
} else {
rb = rb->rb_left;
@ -446,12 +412,6 @@ struct dma_buf *drm_gem_prime_handle_to_dmabuf(struct drm_device *dev,
goto out_unlock;
}
dmabuf = drm_prime_lookup_buf_by_handle(&file_priv->prime, handle);
if (dmabuf) {
get_dma_buf(dmabuf);
goto out;
}
mutex_lock(&dev->object_name_lock);
/* re-export the original imported/exported object */
if (obj->dma_buf) {