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Message-id: <51ADC48E.80907@samsung.com> Date: Tue, 04 Jun 2013 19:42:22 +0900 From: 김승우 <sw0312.kim@...sung.com> To: dri-devel <dri-devel@...ts.freedesktop.org>, "linux-media@...r.kernel.org" <linux-media@...r.kernel.org>, "linaro-mm-sig@...ts.linaro.org" <linaro-mm-sig@...ts.linaro.org>, Sumit Semwal <sumit.semwal@...aro.org>, Dave Airlie <airlied@...ux.ie>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, Inki Dae <inki.dae@...sung.com>, Kyungmin Park <kyungmin.park@...sung.com>, Seung-Woo Kim <sw0312.kim@...sung.com> Subject: Re: [RFC][PATCH 0/2] dma-buf: add importer private data for reimporting 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@...sung.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. 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. > > 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. > > 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. 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. Best Regards, - Seung-Woo Kim > > Cheers, Daniel > -- Seung-Woo Kim Samsung Software R&D Center -- -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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