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.koe...@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.koe...@amd.com>
>> Reviewed-by: Simona Vetter <simona.vet...@ffwll.ch>
>> Reviewed-by: Dmitry Osipenko <dmitry.osipe...@collabora.com>
>> Link:
>> https://patchwork.freedesktop.org/patch/msgid/20250211163109.12200-5-christian.koe...@amd.com
>>
>> 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 <tzimmerm...@suse.de>
>>>>>>> Fixes: b57aa47d39e9 ("drm/gem: Test for imported GEM buffers with
>>>>>>> helper")
>>>>>>> Reported-by: Andy Yan <andys...@163.com>
>>>>>>> Closes:
>>>>>>> https://lore.kernel.org/dri-devel/38d09d34.4354.196379aa560.coremail.andys...@163.com/
>>>>>>> Tested-by: Andy Yan <andys...@163.com>
>>>>>>> Cc: Thomas Zimmermann <tzimmerm...@suse.de>
>>>>>>> Cc: Anusha Srivatsa <asriv...@redhat.com>
>>>>>>> Cc: Christian König <christian.koe...@amd.com>
>>>>>>> Cc: Maarten Lankhorst <maarten.lankho...@linux.intel.com>
>>>>>>> Cc: Maxime Ripard <mrip...@kernel.org>
>>>>>>> Cc: David Airlie <airl...@gmail.com>
>>>>>>> Cc: Simona Vetter <sim...@ffwll.ch>
>>>>>>> Cc: Sumit Semwal <sumit.sem...@linaro.org>
>>>>>>> Cc: "Christian König" <christian.koe...@amd.com>
>>>>>>> Cc: dri-devel@lists.freedesktop.org
>>>>>>> Cc: linux-me...@vger.kernel.org
>>>>>>> Cc: linaro-mm-...@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
>
