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 b71da71a3dd8..edd0051d849f 100644 --- a/drivers/gpu/drm/msm/msm_gem_submit.c +++ b/drivers/gpu/drm/msm/msm_gem_submit.c @@ -306,7 +306,8 @@ 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 = msm_gem_sync_object(&msm_obj->base, submit->ring->fctx,