From: Daniel Vetter <daniel@ffwll.ch>
To: "Koenig, Christian" <Christian.Koenig@amd.com>
Cc: Daniel Vetter <daniel@ffwll.ch>,
"dri-devel@lists.freedesktop.org"
<dri-devel@lists.freedesktop.org>,
"sumit.semwal@linaro.org" <sumit.semwal@linaro.org>,
"linaro-mm-sig@lists.linaro.org" <linaro-mm-sig@lists.linaro.org>,
"linux-media@vger.kernel.org" <linux-media@vger.kernel.org>,
"intel-gfx@lists.freedesktop.org"
<intel-gfx@lists.freedesktop.org>
Subject: Re: [PATCH 1/4] dma-buf: change DMA-buf locking convention
Date: Tue, 8 Oct 2019 10:55:43 +0200 [thread overview]
Message-ID: <20191008085543.GF16989@phenom.ffwll.local> (raw)
In-Reply-To: <be8abe51-05f5-bd06-2633-0d32828e0e43@amd.com>
On Wed, Oct 02, 2019 at 08:37:50AM +0000, Koenig, Christian wrote:
> Hi Daniel,
>
> once more a ping on this. Any more comments or can we get it comitted?
Sorry got a bit smashed past weeks, but should be resurrected now back
from xdc.
-Daniel
>
> Thanks,
> Christian.
>
> Am 24.09.19 um 11:50 schrieb Christian König:
> > Am 17.09.19 um 16:56 schrieb Daniel Vetter:
> >> [SNIP]
> >>>>>>>>>>>> + /* When either the importer or the exporter
> >>>>>>>>>>>> can't handle dynamic
> >>>>>>>>>>>> + * mappings we cache the mapping here to avoid issues
> >>>>>>>>>>>> with the
> >>>>>>>>>>>> + * reservation object lock.
> >>>>>>>>>>>> + */
> >>>>>>>>>>>> + if (dma_buf_attachment_is_dynamic(attach) !=
> >>>>>>>>>>>> + dma_buf_is_dynamic(dmabuf)) {
> >>>>>>>>>>>> + struct sg_table *sgt;
> >>>>>>>>>>>> +
> >>>>>>>>>>>> + if (dma_buf_is_dynamic(attach->dmabuf))
> >>>>>>>>>>>> + dma_resv_lock(attach->dmabuf->resv, NULL);
> >>>>>>>>>>>> +
> >>>>>>>>>>>> + sgt = dmabuf->ops->map_dma_buf(attach,
> >>>>>>>>>>>> DMA_BIDIRECTIONAL);
> >>>>>>>>>>> Now we're back to enforcing DMA_BIDI, which works nicely
> >>>>>>>>>>> around the
> >>>>>>>>>>> locking pain, but apparently upsets the arm-soc folks who
> >>>>>>>>>>> want to
> >>>>>>>>>>> control
> >>>>>>>>>>> this better.
> >>>>>>>>>> Take another look at dma_buf_map_attachment(), we still try
> >>>>>>>>>> to get the
> >>>>>>>>>> caching there for ARM.
> >>>>>>>>>>
> >>>>>>>>>> What we do here is to bidirectionally map the buffer to avoid
> >>>>>>>>>> the
> >>>>>>>>>> locking hydra when importer and exporter disagree on locking.
> >>>>>>>>>>
> >>>>>>>>>> So the ARM folks can easily avoid that by switching to
> >>>>>>>>>> dynamic locking
> >>>>>>>>>> for both.
> >>>>>>>> So you still break the contract between importer and exporter,
> >>>>>>>> except not
> >>>>>>>> for anything that's run in intel-gfx-ci so all is good?
> >>>>>>> No, the contract between importer and exporter stays exactly the
> >>>>>>> same it
> >>>>>>> is currently as long as you don't switch to dynamic dma-buf
> >>>>>>> handling.
> >>>>>>>
> >>>>>>> There is no functional change for the ARM folks here. The only
> >>>>>>> change
> >>>>>>> which takes effect is between i915 and amdgpu and that is perfectly
> >>>>>>> covered by intel-gfx-ci.
> >>>>>> There's people who want to run amdgpu on ARM?
> >>>>> Sure there are, we even recently fixed some bugs for this.
> >>>>>
> >>>>> But as far as I know there is no one currently which is affect by
> >>>>> this
> >>>>> change on ARM with amdgpu.
> >>>> But don't you break them with this now?
> >>> No, we see the bidirectional attachment as compatible with the other
> >>> ones.
> >>>
> >>>> amdgpu will soon set the dynamic flag on exports, which forces the
> >>>> caching
> >>>> at create time (to avoid the locking fun), which will then result in a
> >>>> EBUSY at map_attachment time because we have a cached mapping, but
> >>>> it's
> >>>> the wrong type.
> >>> See the check in dma_buf_map_attachment():
> >>>
> >>> if (attach->dir != direction && attach->dir != DMA_BIDIRECTIONAL)
> >>> return ERR_PTR(-EBUSY);
> >> Hm, I misread this. So yeah should work, +/- the issue that we might
> >> not flush enough. But I guess that can be fixed whenever, it's not
> >> like dma-api semantics are a great fit for us. Maybe a fixme comment
> >> would be useful here ... I'll look at this tomorrow or so because atm
> >> brain is slow, I'm down with the usual post-conference cold it seems
> >> :-/
> >
> > Hope your are feeling better now, adding a comment is of course not a
> > problem.
> >
> > With that fixed can I get an reviewed-by or at least and acked-by?
> >
> > I want to land at least some parts of those changes now.
> >
> > Regards,
> > Christian.
> >
> >> -Daniel
> >>
> >
>
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
next prev parent reply other threads:[~2019-10-08 8:55 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-29 14:29 Dynamic DMA-buf locking changes Christian König
2019-08-29 14:29 ` [PATCH 1/4] dma-buf: change DMA-buf locking convention Christian König
2019-09-03 8:05 ` Daniel Vetter
2019-09-11 10:53 ` Christian König
2019-09-16 12:23 ` Christian König
2019-09-17 12:31 ` Daniel Vetter
2019-09-17 12:40 ` Koenig, Christian
2019-09-17 13:13 ` Daniel Vetter
2019-09-17 13:24 ` Koenig, Christian
2019-09-17 13:45 ` Daniel Vetter
2019-09-17 14:47 ` Koenig, Christian
2019-09-17 14:56 ` Daniel Vetter
2019-09-24 9:51 ` Koenig, Christian
2019-10-02 8:37 ` Koenig, Christian
2019-10-08 8:55 ` Daniel Vetter [this message]
2019-10-16 13:46 ` Koenig, Christian
2019-10-16 14:23 ` Daniel Vetter
2019-10-17 9:04 ` Koenig, Christian
2019-10-08 8:55 ` Daniel Vetter
2019-08-29 14:29 ` [PATCH 2/4] drm/ttm: use the parent resv for ghost objects v2 Christian König
2019-10-08 9:25 ` Daniel Vetter
2019-10-09 13:10 ` Christian König
2019-10-09 14:09 ` Daniel Vetter
2019-08-29 14:29 ` [PATCH 3/4] drm/amdgpu: add independent DMA-buf export v7 Christian König
2019-08-29 14:29 ` [PATCH 4/4] drm/amdgpu: add independent DMA-buf import v8 Christian König
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