[Intel-gfx] [PATCH v5 16/20] drm/msm: Don't break exclusive fence ordering

Daniel Vetter
2021-08-05T10:48:06Z

There's only one exclusive slot, and we must not break the ordering.

Adding a new exclusive fence drops all previous fences from the
dma_resv. To avoid violating the signalling order we err on the side of
over-synchronizing by waiting for the existing fences, even if
userspace asked us to ignore them.

A better fix would be to us a dma_fence_chain or _array like e.g.
amdgpu now uses, but
- msm has a synchronous dma_fence_wait for anything from another
context, so doesn't seem to care much,
- and it probably makes sense to lift this into dma-resv.c code as a
proper concept, so that drivers don't have to hack up their own
solution each on their own.

v2: Improve commit message per Lucas' suggestion.

Cc: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Rob Clark <robdclark@gmail.com>
Cc: Sean Paul <sean@poorly.run>
Cc: linux-arm-msm@vger.kernel.org
Cc: freedreno@lists.freedesktop.org
---
drivers/gpu/drm/msm/msm_gem_submit.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/msm/msm_gem_submit.c b/drivers/gpu/drm/msm/msm_gem_submit.c
index fb5a2eab27a2..66633dfd58a2 100644
--- a/drivers/gpu/drm/msm/msm_gem_submit.c
+++ b/drivers/gpu/drm/msm/msm_gem_submit.c
@@ -330,7 +330,8 @@ static int submit_fence_sync(struct msm_gem_submit *submit, bool no_implicit)
return ret;
}

- if (no_implicit)
+ /* exclusive fences must be ordered */
+ if (no_implicit && !write)
continue;

ret = drm_sched_job_add_implicit_dependencies(&submit->base,
--
2.32.0