On Thu, 27 Nov 2025 09:58:55 +0100 Thomas Zimmermann <[email protected]> wrote:
> Hi > > Am 27.11.25 um 09:42 schrieb Thomas Zimmermann: > > 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. > > I think, instead of looking at the ops field, the test could look at > dma_buf->owner == dev->driver->fops->owner. This will tell if the > dma_buf comes from the same driver and hence is a GEM object. In the > next step, do obj->dev == dev as before. This will also allow drivers > like amdgpu to use the helper for testing. See [1]. Except this doesn't work when the driver is linked statically (not enabled as a module), because THIS_MODULE is NULL in that case.
