dma-fence: Document recoverable page fault implications
authorDaniel Vetter <daniel.vetter@ffwll.ch>
Wed, 3 Feb 2021 15:29:21 +0000 (16:29 +0100)
committerDaniel Vetter <daniel.vetter@ffwll.ch>
Fri, 12 Mar 2021 14:10:03 +0000 (15:10 +0100)
commit8613385cb2856e2ee9c4efb1f95eeaca0e1a0963
tree19d5d30f09b4f37941fd68fab1637578d76c38b3
parent67cc24ac17fe2a2496456c8ca281ef89f7a6fd89
dma-fence: Document recoverable page fault implications

Recently there was a fairly long thread about recoreable hardware page
faults, how they can deadlock, and what to do about that.

While the discussion is still fresh I figured good time to try and
document the conclusions a bit. This documentation section explains
what's the potential problem, and the remedies we've discussed,
roughly ordered from best to worst.

v2: Linus -> Linux typoe (Dave)

v3:
- Make it clear drivers only need to implement one option (Christian)
- Make it clearer that implicit sync is out the window with exclusive
  fences (Christian)
- Add the fairly theoretical option of segementing the memory (either
  statically or through dynamic checks at runtime for which piece of
  memory is managed how) and explain why it's not a great idea (Felix)

References: https://lore.kernel.org/dri-devel/20210107030127.20393-1-Felix.Kuehling@amd.com/
Reviewed-by: Christian König <christian.koenig@amd.com>
Acked-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
c: Dave Airlie <airlied@gmail.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Thomas Hellström <thomas.hellstrom@intel.com>
Cc: "Christian König" <christian.koenig@amd.com>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: Felix Kuehling <felix.kuehling@amd.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: linux-media@vger.kernel.org
Cc: linaro-mm-sig@lists.linaro.org
Link: https://patchwork.freedesktop.org/patch/msgid/20210203152921.2429937-1-daniel.vetter@ffwll.ch
Documentation/driver-api/dma-buf.rst