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....@samsung.com> > > 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. 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. 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. Cheers, Daniel -- Daniel Vetter Software Engineer, Intel Corporation +41 (0) 79 365 57 48 - http://blog.ffwll.ch -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/