On Tue, Jun 04, 2013 at 07:42:22PM +0900, 김승우 wrote: > > > On 2013년 06월 01일 00:29, Daniel Vetter wrote: > > On Fri, May 31, 2013 at 07:22:24PM +0900, 김승우 wrote: > >> Hello Daniel, > >> > >> Thanks for your comment. > >> > >> On 2013년 05월 31일 18:14, Daniel Vetter wrote: > >>> On Fri, May 31, 2013 at 10:54 AM, Seung-Woo Kim <sw0312.kim@xxxxxxxxxxx> wrote: > >>>> importer private data in dma-buf attachment can be used by importer to > >>>> reimport same dma-buf. > >>>> > >>>> Seung-Woo Kim (2): > >>>> dma-buf: add importer private data to attachment > >>>> drm/prime: find gem object from the reimported dma-buf > >>> > >>> Self-import should already work (at least with the latest refcount > >>> fixes merged). At least the tests to check both re-import on the same > >>> drm fd and on a different all work as expected now. > >> > >> Currently, prime works well for all case including self-importing, > >> importing, and reimporting as you describe. Just, importing dma-buf from > >> other driver twice with different drm_fd, each import create its own gem > >> object even two import is done for same buffer because prime_priv is in > >> struct drm_file. This means mapping to the device is done also twice. > >> IMHO, these duplicated creations and maps are not necessary if drm can > >> find previous import in different prime_priv. > > > > Well, that's imo a bug with the other driver. If it doesn't export > > something really simple (e.g. contiguous memory which doesn't require any > > mmio resources at all) it should have a cache of exported dma_buf fds so > > that it hands out the same dma_buf every time. > > Hm, all existing dma-buf exporter including i915 driver implements its > map_dma_buf callback as allocating scatter-gather table with pages in > its buffer and calling dma_map_sg() with the sgt. With different > drm_fds, importing one dma-buf *twice*, then importer calls > dma_buf_attach() and dma_buf_map_attachment() twice at least in drm > importer because re-importing case can only checked with prime_priv in > drm_file as I described. Well, but thanks to all the self-import and re-import checks, it's _impossible_ to import the same dma_buf twice without noticing (presuming both importer and exporter are drm devices). > > > > > Or it needs to be more clever in it's dma_buf_attachment_map functions and > > lookup up a pre-existing iommu mapping. > > > > But dealing with this in the importer is just broken. > > > >>> Second, the dma_buf_attachment is _definitely_ the wrong place to do > >>> this. If you need iommu mapping caching, that should happen at a lower > >>> level (i.e. in the map_attachment callback somewhere of the exporter, > >>> that's what the priv field in the attachment is for). Snatching away > >>> the attachement from some random other import is certainly not the way > >>> to go - attachements are _not_ refcounted! > >> > >> Yes, attachments do not have refcount, so importer should handle and drm > >> case in my patch, importer private data is gem object and it has, of > >> course, refcount. > >> > >> And at current, exporter can not classify map_dma_buf requests of same > >> importer to same buffer with different attachment because dma_buf_attach > >> always makes new attachments. To resolve this exporter should search all > >> different attachment from same importer of dma-buf and it seems more > >> complex than importer private data to me. > >> > >> If I misunderstood something, please let me know. > > > > Like I've said above, just fix this in the exporter. If an importer sees > > two different dma_bufs it can very well presume that it those two indeed > > point to different backing storage. > > Yes, my patch does not break this concept. I just fixed case importing > _one_ dma-buf twice with different drm_fds. See above, if you have two different struct file * for the same underlying buffer object something is wrong already. > > This will be even more important if we attach fences two dma_bufs. If your > > broken exporter creates multiple dma_bufs each one of them will have their > > own fences attached, leading to a complete disasters. Ok, strictly > > speaking if you keep the same reservation pointer for each dma_buf it'll > > work, but that's just a detail of how you solve this in the exporter. > > I can not understand about broken exporter you addressed. I don't mean > exporter makes dma-bufs from one backing storage. > While, my patch prevents not to create drm gem objects from one back > storage by importing one dma-buf with different drm-fds. Well, we also have code in drm prime for that case - if the same dma_buf object shows up multiple times, we'll only import it once. For the second import we'll return the already created drm_gem object from the first import, but with the refcount incremented. > I do not believe the fix of importer is the best way, but at this > moment, I have no idea how I can fix the exporter for this issue. I think if you have drm prime drivers both as importers and exporters, it is already fixed. It is correct though that both importer and exporter need a bit of code to take care and not accidentally duplicate a shared object somehow. But since you've proposed your rfc as part of the drm subsystem I've figured that we don't need to discuss the duplicate import handling code. Yours, Daniel -- Daniel Vetter Software Engineer, Intel Corporation +41 (0) 79 365 57 48 - http://blog.ffwll.ch _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/dri-devel
