From: Tomasz Figa <tfiga@chromium.org>
To: Rob Clark <robdclark@gmail.com>, Christoph Hellwig <hch@lst.de>,
Robin Murphy <robin.murphy@arm.com>,
Vivek Gautam <vivek.gautam@codeaurora.org>
Cc: David Airlie <airlied@linux.ie>,
dri-devel <dri-devel@lists.freedesktop.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
freedreno <freedreno@lists.freedesktop.org>,
Archit Taneja <architt@codeaurora.org>,
linux-arm-msm <linux-arm-msm@vger.kernel.org>,
Sean Paul <seanpaul@chromium.org>
Subject: Re: [PATCH v3 1/1] drm: msm: Replace dma_map_sg with dma_sync_sg*
Date: Fri, 30 Nov 2018 18:05:12 -0800 [thread overview]
Message-ID: <CAAFQd5DMgGDPcK=4DktfC7T9O0MrU1VBqJqR+6VYpOh_DdEXUg@mail.gmail.com> (raw)
In-Reply-To: <CAAFQd5CEXZU5x+Fi5kRHZFfBwPkUbpo=-UBTARiaAoLqV-tMww@mail.gmail.com>
On Thu, Nov 29, 2018 at 4:23 PM Tomasz Figa <tfiga@chromium.org> wrote:
>
> On Thu, Nov 29, 2018 at 12:03 PM Robin Murphy <robin.murphy@arm.com> wrote:
> >
> > On 29/11/2018 19:57, Tomasz Figa wrote:
> > > On Thu, Nov 29, 2018 at 11:40 AM Jordan Crouse <jcrouse@codeaurora.org> wrote:
> > >>
> > >> On Thu, Nov 29, 2018 at 01:48:15PM -0500, Rob Clark wrote:
> > >>> On Thu, Nov 29, 2018 at 10:54 AM Christoph Hellwig <hch@lst.de> wrote:
> > >>>>
> > >>>> On Thu, Nov 29, 2018 at 09:42:50AM -0500, Rob Clark wrote:
> > >>>>> Maybe the thing we need to do is just implement a blacklist of
> > >>>>> compatible strings for devices which should skip the automatic
> > >>>>> iommu/dma hookup. Maybe a bit ugly, but it would also solve a problem
> > >>>>> preventing us from enabling per-process pagetables for a5xx (where we
> > >>>>> need to control the domain/context-bank that is allocated by the dma
> > >>>>> api).
> > >>>>
> > >>>> You can detach from the dma map attachment using arm_iommu_detach_device,
> > >>>> which a few drm drivers do, but I don't think this is the problem.
> > >>>
> > >>> I think even with detach, we wouldn't end up with the context-bank
> > >>> that the gpu firmware was hard-coded to expect, and so it would
> > >>> overwrite the incorrect page table address register. (I could be
> > >>> mis-remembering that, Jordan spent more time looking at that. But it
> > >>> was something along those lines.)
> > >>
> > >> Right - basically the DMA domain steals context bank 0 and the GPU is hard coded
> > >> to use that context bank for pagetable switching.
> > >>
> > >> I believe the Tegra guys also had a similar problem with a hard coded context
> > >> bank.
> >
> > AIUI, they don't need a specific hardware context, they just need to
> > know which one they're actually using, which the domain abstraction hides.
> >
> > > Wait, if we detach the GPU/display struct device from the default
> > > domain and attach it to a newly allocated domain, wouldn't the newly
> > > allocated domain use the context bank we need? Note that we're already
> >
> > The arm-smmu driver doesn't, but there's no fundamental reason it
> > couldn't. That should just need code to refcount domain users and
> > release hardware contexts for domains with no devices currently attached.
> >
> > Robin.
> >
> > > doing that, except that we're doing it behind the back of the DMA
> > > mapping subsystem, so that it keeps using the IOMMU version of the DMA
> > > ops for the device and doing any mapping operations on the default
> > > domain. If we ask the DMA mapping to detach, wouldn't it essentially
> > > solve the problem?
>
> Thanks Robin.
>
> Still, my point is that the MSM DRM driver attaches the GPU struct
> device to a new domain it allocates using iommu_domain_alloc() and it
> seems to work fine, so I believe it's not the problem we're looking
> into with this patch.
Could we just make the MSM DRM call arch_teardown_dma_ops() and then
arch_setup_dma_ops() with the `iommu` argument set to NULL and be done
with it?
Best regards,
Tomasz
next prev parent reply other threads:[~2018-12-01 2:05 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-29 14:03 [PATCH v3 1/1] drm: msm: Replace dma_map_sg with dma_sync_sg* Vivek Gautam
2018-11-29 14:14 ` Christoph Hellwig
2018-11-29 14:25 ` Rob Clark
2018-11-29 14:42 ` Rob Clark
2018-11-29 15:54 ` Christoph Hellwig
2018-11-29 18:48 ` Rob Clark
2018-11-29 19:40 ` Jordan Crouse
2018-11-29 19:57 ` Tomasz Figa
2018-11-29 20:03 ` Robin Murphy
2018-11-30 0:23 ` Tomasz Figa
2018-12-01 2:05 ` Tomasz Figa [this message]
2018-12-01 11:46 ` Rob Clark
2018-12-03 0:12 ` Tomasz Figa
2018-11-29 14:43 ` Daniel Vetter
2018-11-29 15:57 ` Christoph Hellwig
2018-11-29 16:28 ` Daniel Vetter
2018-11-29 16:57 ` Christoph Hellwig
2018-11-29 17:09 ` Daniel Vetter
2018-11-29 17:24 ` Tomasz Figa
2018-11-29 18:35 ` Christoph Hellwig
2018-11-29 18:57 ` Rob Clark
2018-11-30 9:40 ` Daniel Vetter
2018-11-30 9:35 ` Daniel Vetter
2018-11-30 9:44 ` Christoph Hellwig
2018-11-29 18:33 ` Christoph Hellwig
2018-11-30 9:46 ` Daniel Vetter
2018-12-07 1:38 ` Christoph Hellwig
2018-12-07 14:29 ` Rob Clark
2018-11-29 17:33 ` Brian Starkey
2018-11-29 18:35 ` Christoph Hellwig
2018-11-30 1:15 ` Rob Clark
2018-11-30 9:35 ` Christoph Hellwig
2018-11-29 15:53 ` Christoph Hellwig
2018-11-29 18:44 ` Rob Clark
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