Am 15.04.25 um 15:14 schrieb Thomas Zimmermann:
The long-term goal is to make import_attach optional because its setup requires a DMA-capable device.
HUI WHAT?
Dmitry and I put quite some effort into being able to create an import_attach without the requirement to have a DMA-capable device.
The last puzzle piece of that landed a month ago in the form of this patch here:
commit b72f66f22c0e39ae6684c43fead774c13db24e73 Author: Christian König christian.koenig@amd.com Date: Tue Feb 11 17:20:53 2025 +0100
dma-buf: drop caching of sg_tables That was purely for the transition from static to dynamic dma-buf handling and can be removed again now. Signed-off-by: Christian König christian.koenig@amd.com Reviewed-by: Simona Vetter simona.vetter@ffwll.ch Reviewed-by: Dmitry Osipenko dmitry.osipenko@collabora.com Link: https://patchwork.freedesktop.org/patch/msgid/20250211163109.12200-5-christi...
When you don't create an import attachment the exporter wouldn't know that his buffer is actually used which is usually a quite bad idea.
This is for devices who only want to do a vmap of the buffer, isn't it?
Yeah, the vmap needs the sgtable, which needs import_attach IIRC. Somewhere in there a DMA device is required. But it's not of high priority as we have workarounds.
I've removed the need to create an sgtable just to create an import_attach.
The crux is that exporters sometimes need to distinct between the case when DMA-buf is just used for inter process passing of buffers and inter device passing of buffers. Usually we use the list of attachments for that.
Because of this I though of changing the dma_buf_vmap functions to take an attachment instead of an dma_buf as parameter. That would also resolve the problem is making sure to signal buffer movement through the move notifier.
BTW: Where do we currently pin the buffers to make sure that the pointers returned by dma_buf_vmap() stays valid after dropping the reservation lock?
Regards, Christian.
Best regards Thomas
Regards, Christian.
Best regards Thomas
Regards, Christian.
Best regards Thomas
Regards, Christian.
> Signed-off-by: Thomas Zimmermann tzimmermann@suse.de > Fixes: b57aa47d39e9 ("drm/gem: Test for imported GEM buffers with helper") > Reported-by: Andy Yan andyshrk@163.com > Closes: https://lore.kernel.org/dri-devel/38d09d34.4354.196379aa560.Coremail.andyshr... > Tested-by: Andy Yan andyshrk@163.com > Cc: Thomas Zimmermann tzimmermann@suse.de > Cc: Anusha Srivatsa asrivats@redhat.com > Cc: Christian König christian.koenig@amd.com > Cc: Maarten Lankhorst maarten.lankhorst@linux.intel.com > Cc: Maxime Ripard mripard@kernel.org > Cc: David Airlie airlied@gmail.com > Cc: Simona Vetter simona@ffwll.ch > Cc: Sumit Semwal sumit.semwal@linaro.org > Cc: "Christian König" christian.koenig@amd.com > Cc: dri-devel@lists.freedesktop.org > Cc: linux-media@vger.kernel.org > Cc: linaro-mm-sig@lists.linaro.org > --- > include/drm/drm_gem.h | 8 +++++++- > 1 file changed, 7 insertions(+), 1 deletion(-) > > diff --git a/include/drm/drm_gem.h b/include/drm/drm_gem.h > index 9b71f7a9f3f8..f09b8afcf86d 100644 > --- a/include/drm/drm_gem.h > +++ b/include/drm/drm_gem.h > @@ -589,7 +589,13 @@ static inline bool drm_gem_object_is_shared_for_memory_stats(struct drm_gem_obje > static inline bool drm_gem_is_imported(const struct drm_gem_object *obj) > { > /* The dma-buf's priv field points to the original GEM object. */ > - return obj->dma_buf && (obj->dma_buf->priv != obj); > + return (obj->dma_buf && (obj->dma_buf->priv != obj)) || > + /* > + * TODO: During object release, the dma-buf might already > + * be gone. For now keep testing import_attach, but > + * this should be removed at some point. > + */ > + obj->import_attach; > } > #ifdef CONFIG_LOCKDEP