On Thu, 27 Nov 2025 09:34:43 +0100 Thomas Zimmermann <[email protected]> wrote:
> 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. First, it's no longer a callback, but a pointer to dma_buf_ops (joking of course, I get what you mean :P). > 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. It doesn't work because we need an ops to test against when a dma_buf is imported, and that information has to be available at the drm_{device,driver} level. > > 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; > > 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. Nope, because dma_buf::ops needs to be tested against the driver dma_buf_ops to determine if it's a drm_gem_object that's stored in dma_buf::priv. If we add such a callback, it has to be at the drm_driver level.
