From: Thierry Reding <treding@nvidia.com> To: Christoph Hellwig <hch@infradead.org> Cc: "Daniel Vetter" <daniel@ffwll.ch>, "Christian König" <christian.koenig@amd.com>, "moderated list:DMA BUFFER SHARING FRAMEWORK" <linaro-mm-sig@lists.linaro.org>, "Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>, "amd-gfx list" <amd-gfx@lists.freedesktop.org>, "Jerome Glisse" <jglisse@redhat.com>, dri-devel <dri-devel@lists.freedesktop.org>, "Dan Williams" <dan.j.williams@intel.com>, "Logan Gunthorpe" <logang@deltatee.com>, "open list:DMA BUFFER SHARING FRAMEWORK" <linux-media@vger.kernel.org> Subject: Re: [Linaro-mm-sig] [PATCH 4/8] dma-buf: add peer2peer flag Date: Wed, 25 Apr 2018 09:41:51 +0200 [thread overview] Message-ID: <20180425074151.GA2271@ulmo> (raw) In-Reply-To: <20180425064335.GB28100@infradead.org> [-- Attachment #1: Type: text/plain, Size: 2182 bytes --] On Tue, Apr 24, 2018 at 11:43:35PM -0700, Christoph Hellwig wrote: > On Wed, Apr 25, 2018 at 08:23:15AM +0200, Daniel Vetter wrote: > > For more fun: > > > > https://www.spinics.net/lists/dri-devel/msg173630.html > > > > Yeah, sometimes we want to disable the iommu because the on-gpu > > pagetables are faster ... > > I am not on this list, but remote NAK from here. This needs an > API from the iommu/dma-mapping code. Drivers have no business poking > into these details. The interfaces that the above patch uses are all EXPORT_SYMBOL_GPL, which is rather misleading if they are not meant to be used by drivers directly. > Thierry, please resend this with at least the iommu list and > linux-arm-kernel in Cc to have a proper discussion on the right API. I'm certainly open to help with finding a correct solution, but the patch above was purposefully terse because this is something that I hope we can get backported to v4.16 to unbreak Nouveau. Coordinating such a backport between ARM and DRM trees does not sound like something that would help getting this fixed in v4.16. The fundamental issue here is that the DMA/IOMMU integration is something that has caused a number of surprising regressions in the past because it tends to sneak in unexpectedly. For example the current regression shows up only if CONFIG_ARM_DMA_USE_IOMMU=y because the DMA API will then transparently create a second mapping and mess things up. Everything works fine if that option is disabled. This is ultimately why we didn't notice, since we don't enable that option by default. I do have a patch that I plan to apply to the Tegra tree that will always enable CONFIG_ARM_DMA_USE_IOMMU=y on Tegra to avoid any such surprises in the future, but I can obviously only apply that once the above patch is applied to Nouveau, otherwise we'll break Nouveau unconditionally. Granted, this issue could've been caught with a little more testing, but in retrospect I think it would've been a lot better if ARM_DMA_USE_IOMMU was just enabled unconditionally if it has side-effects that platforms don't opt in to but have to explicitly opt out of. Thierry [-- Attachment #2: signature.asc --] [-- Type: application/pgp-signature, Size: 833 bytes --]
WARNING: multiple messages have this Message-ID (diff)
From: Thierry Reding <treding@nvidia.com> To: Christoph Hellwig <hch@infradead.org> Cc: "Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>, "amd-gfx list" <amd-gfx@lists.freedesktop.org>, "moderated list:DMA BUFFER SHARING FRAMEWORK" <linaro-mm-sig@lists.linaro.org>, "Jerome Glisse" <jglisse@redhat.com>, dri-devel <dri-devel@lists.freedesktop.org>, "Dan Williams" <dan.j.williams@intel.com>, "Logan Gunthorpe" <logang@deltatee.com>, "Christian König" <christian.koenig@amd.com>, "open list:DMA BUFFER SHARING FRAMEWORK" <linux-media@vger.kernel.org> Subject: Re: [Linaro-mm-sig] [PATCH 4/8] dma-buf: add peer2peer flag Date: Wed, 25 Apr 2018 09:41:51 +0200 [thread overview] Message-ID: <20180425074151.GA2271@ulmo> (raw) In-Reply-To: <20180425064335.GB28100@infradead.org> [-- Attachment #1.1: Type: text/plain, Size: 2182 bytes --] On Tue, Apr 24, 2018 at 11:43:35PM -0700, Christoph Hellwig wrote: > On Wed, Apr 25, 2018 at 08:23:15AM +0200, Daniel Vetter wrote: > > For more fun: > > > > https://www.spinics.net/lists/dri-devel/msg173630.html > > > > Yeah, sometimes we want to disable the iommu because the on-gpu > > pagetables are faster ... > > I am not on this list, but remote NAK from here. This needs an > API from the iommu/dma-mapping code. Drivers have no business poking > into these details. The interfaces that the above patch uses are all EXPORT_SYMBOL_GPL, which is rather misleading if they are not meant to be used by drivers directly. > Thierry, please resend this with at least the iommu list and > linux-arm-kernel in Cc to have a proper discussion on the right API. I'm certainly open to help with finding a correct solution, but the patch above was purposefully terse because this is something that I hope we can get backported to v4.16 to unbreak Nouveau. Coordinating such a backport between ARM and DRM trees does not sound like something that would help getting this fixed in v4.16. The fundamental issue here is that the DMA/IOMMU integration is something that has caused a number of surprising regressions in the past because it tends to sneak in unexpectedly. For example the current regression shows up only if CONFIG_ARM_DMA_USE_IOMMU=y because the DMA API will then transparently create a second mapping and mess things up. Everything works fine if that option is disabled. This is ultimately why we didn't notice, since we don't enable that option by default. I do have a patch that I plan to apply to the Tegra tree that will always enable CONFIG_ARM_DMA_USE_IOMMU=y on Tegra to avoid any such surprises in the future, but I can obviously only apply that once the above patch is applied to Nouveau, otherwise we'll break Nouveau unconditionally. Granted, this issue could've been caught with a little more testing, but in retrospect I think it would've been a lot better if ARM_DMA_USE_IOMMU was just enabled unconditionally if it has side-effects that platforms don't opt in to but have to explicitly opt out of. Thierry [-- Attachment #1.2: signature.asc --] [-- Type: application/pgp-signature, Size: 833 bytes --] [-- Attachment #2: Type: text/plain, Size: 160 bytes --] _______________________________________________ dri-devel mailing list dri-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/dri-devel
next prev parent reply other threads:[~2018-04-25 7:42 UTC|newest] Thread overview: 161+ messages / expand[flat|nested] mbox.gz Atom feed top 2018-03-25 10:59 [PATCH 1/8] lib/scatterlist: add sg_set_dma_addr() helper Christian König 2018-03-25 10:59 ` Christian König 2018-03-25 10:59 ` [PATCH 2/8] PCI: Add pci_find_common_upstream_dev() Christian König 2018-03-25 10:59 ` Christian König 2018-03-28 12:38 ` Christoph Hellwig 2018-03-28 15:07 ` Christian König 2018-03-28 15:07 ` Christian König 2018-03-28 15:47 ` Logan Gunthorpe 2018-03-28 16:02 ` Christian König 2018-03-28 16:02 ` Christian König 2018-03-28 16:25 ` Logan Gunthorpe 2018-03-28 18:28 ` Christian König 2018-03-28 18:28 ` Christian König 2018-03-28 18:57 ` Logan Gunthorpe 2018-03-28 19:44 ` Christian König 2018-03-28 19:44 ` Christian König 2018-03-28 19:53 ` Logan Gunthorpe 2018-03-29 11:44 ` Christian König 2018-03-29 15:45 ` Logan Gunthorpe 2018-03-29 16:10 ` Christian König 2018-03-29 16:10 ` Christian König 2018-03-29 16:25 ` Logan Gunthorpe 2018-03-29 18:15 ` Christian König 2018-03-29 18:15 ` Christian König 2018-03-30 1:58 ` Jerome Glisse 2018-03-30 1:58 ` Jerome Glisse 2018-03-30 6:33 ` Christoph Hellwig 2018-03-30 6:33 ` Christoph Hellwig 2018-03-30 15:25 ` Jerome Glisse 2018-03-30 18:46 ` Logan Gunthorpe 2018-03-30 19:45 ` Jerome Glisse 2018-03-30 19:45 ` Jerome Glisse 2018-04-02 17:02 ` Logan Gunthorpe 2018-04-02 17:20 ` Jerome Glisse 2018-04-02 17:20 ` Jerome Glisse 2018-04-02 17:37 ` Logan Gunthorpe 2018-04-02 19:16 ` Jerome Glisse 2018-04-02 19:16 ` Jerome Glisse 2018-04-02 19:32 ` Logan Gunthorpe 2018-04-02 19:45 ` Jerome Glisse 2018-04-02 19:45 ` Jerome Glisse [not found] ` <CADnq5_P-z=Noos_jaME9_CERri3C-m2hPPvx2bArr36O=1FnrA@mail.gmail.com> 2018-03-29 14:37 ` Alex Deucher 2018-03-29 14:37 ` Alex Deucher 2018-03-25 10:59 ` [PATCH 3/8] PCI: Add pci_peer_traffic_supported() Christian König 2018-03-25 10:59 ` Christian König 2018-03-25 10:59 ` [PATCH 4/8] dma-buf: add peer2peer flag Christian König 2018-03-25 10:59 ` Christian König 2018-03-29 6:57 ` Daniel Vetter 2018-03-29 6:57 ` Daniel Vetter 2018-03-29 11:34 ` Christian König 2018-03-29 11:34 ` Christian König 2018-04-03 9:09 ` Daniel Vetter 2018-04-03 9:09 ` Daniel Vetter 2018-04-03 17:06 ` Jerome Glisse 2018-04-03 17:06 ` Jerome Glisse 2018-04-03 18:08 ` Daniel Vetter 2018-04-03 18:08 ` Daniel Vetter 2018-04-16 12:39 ` Christoph Hellwig 2018-04-16 12:39 ` Christoph Hellwig 2018-04-16 13:38 ` Daniel Vetter 2018-04-16 13:38 ` Daniel Vetter 2018-04-19 8:16 ` Christoph Hellwig 2018-04-19 8:16 ` Christoph Hellwig 2018-04-20 7:13 ` Daniel Vetter 2018-04-20 7:13 ` Daniel Vetter 2018-04-20 8:58 ` Christian König 2018-04-20 8:58 ` Christian König 2018-04-20 10:17 ` Christoph Hellwig 2018-04-20 10:17 ` Christoph Hellwig 2018-04-20 10:44 ` Christian König 2018-04-20 10:44 ` Christian König 2018-04-20 12:46 ` Christoph Hellwig 2018-04-20 15:21 ` [Linaro-mm-sig] " Daniel Vetter 2018-04-24 18:48 ` Christoph Hellwig 2018-04-24 18:48 ` Christoph Hellwig 2018-04-24 19:32 ` Daniel Vetter 2018-04-24 19:32 ` Daniel Vetter 2018-04-25 5:48 ` Christoph Hellwig 2018-04-25 5:48 ` Christoph Hellwig 2018-04-25 6:10 ` Alex Deucher 2018-04-25 6:10 ` Alex Deucher 2018-04-25 6:13 ` Daniel Vetter 2018-04-25 6:13 ` Daniel Vetter 2018-04-25 6:23 ` Daniel Vetter 2018-04-25 6:23 ` Daniel Vetter 2018-04-25 6:43 ` Christoph Hellwig 2018-04-25 6:43 ` Christoph Hellwig 2018-04-25 7:02 ` Daniel Vetter 2018-04-25 7:02 ` Daniel Vetter 2018-04-25 7:09 ` Christoph Hellwig 2018-04-25 7:09 ` Christoph Hellwig 2018-04-25 7:30 ` Daniel Vetter 2018-04-25 7:30 ` Daniel Vetter 2018-04-25 7:56 ` Thierry Reding 2018-04-25 7:56 ` Thierry Reding 2018-04-25 8:55 ` Christoph Hellwig 2018-04-25 8:55 ` Christoph Hellwig 2018-04-25 7:43 ` Thierry Reding 2018-04-25 7:43 ` Thierry Reding 2018-04-25 7:41 ` Thierry Reding [this message] 2018-04-25 7:41 ` Thierry Reding 2018-04-25 8:54 ` noveau vs arm dma ops Christoph Hellwig 2018-04-25 8:54 ` Christoph Hellwig 2018-04-25 8:54 ` Christoph Hellwig 2018-04-25 9:25 ` Russell King - ARM Linux 2018-04-25 9:25 ` Russell King - ARM Linux 2018-04-25 10:04 ` Daniel Vetter 2018-04-25 10:04 ` Daniel Vetter 2018-04-25 10:04 ` Daniel Vetter 2018-04-25 15:33 ` Christoph Hellwig 2018-04-25 15:33 ` Christoph Hellwig 2018-04-25 15:33 ` Christoph Hellwig 2018-04-25 21:35 ` Daniel Vetter 2018-04-25 21:35 ` Daniel Vetter 2018-04-25 21:35 ` Daniel Vetter 2018-04-25 23:26 ` Russell King - ARM Linux 2018-04-25 23:26 ` Russell King - ARM Linux 2018-04-26 9:17 ` Daniel Vetter 2018-04-26 9:17 ` Daniel Vetter 2018-04-26 9:17 ` Daniel Vetter 2018-04-26 9:09 ` Christoph Hellwig 2018-04-26 9:09 ` Christoph Hellwig 2018-04-26 9:09 ` Christoph Hellwig 2018-04-26 9:45 ` Daniel Vetter 2018-04-26 9:45 ` Daniel Vetter 2018-04-26 9:45 ` Daniel Vetter 2018-04-26 11:12 ` Russell King - ARM Linux 2018-04-26 11:12 ` Russell King - ARM Linux 2018-04-25 22:54 ` Russell King - ARM Linux 2018-04-25 22:54 ` Russell King - ARM Linux 2018-04-26 9:13 ` Christoph Hellwig 2018-04-26 9:13 ` Christoph Hellwig 2018-04-26 9:13 ` Christoph Hellwig 2018-04-26 9:20 ` [Linaro-mm-sig] " Daniel Vetter 2018-04-26 9:20 ` Daniel Vetter 2018-04-26 9:20 ` Daniel Vetter 2018-04-26 9:24 ` Christoph Hellwig 2018-04-26 9:24 ` Christoph Hellwig 2018-04-26 9:24 ` Christoph Hellwig 2018-04-26 9:39 ` Daniel Vetter 2018-04-26 9:39 ` Daniel Vetter 2018-04-26 9:39 ` Daniel Vetter 2018-04-25 6:24 ` [Linaro-mm-sig] [PATCH 4/8] dma-buf: add peer2peer flag Alex Deucher 2018-04-25 6:24 ` Alex Deucher 2018-04-25 6:41 ` Christoph Hellwig 2018-04-25 6:41 ` Christoph Hellwig 2018-04-25 17:44 ` Alex Deucher 2018-04-25 17:44 ` Alex Deucher 2018-04-25 18:38 ` Dan Williams 2018-04-25 18:38 ` Dan Williams 2018-05-04 12:45 ` Lucas Stach 2018-03-25 10:59 ` [PATCH 5/8] drm/amdgpu: print DMA-buf status in debugfs Christian König 2018-03-25 10:59 ` Christian König 2018-03-25 10:59 ` [PATCH 6/8] drm/amdgpu: note that we can handle peer2peer DMA-buf Christian König 2018-03-25 10:59 ` Christian König 2018-03-25 10:59 ` [PATCH 7/8] drm/amdgpu: add amdgpu_gem_attach Christian König 2018-03-25 10:59 ` Christian König 2018-03-25 11:00 ` [PATCH 8/8] drm/amdgpu: add support for exporting VRAM using DMA-buf Christian König 2018-03-25 11:00 ` Christian König 2018-03-28 12:37 ` [PATCH 1/8] lib/scatterlist: add sg_set_dma_addr() helper Christoph Hellwig 2018-03-28 12:37 ` Christoph Hellwig
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