Re: [PATCH] drm/syncobj: Allow wait for submit and signal behavior (v2)

Quoting Jason Ekstrand (2017-08-09 18:00:54)

+static signed long drm_syncobj_array_wait_timeout(struct drm_syncobj **syncobjs,

•                                             uint32_t count,
  

•                                             uint32_t flags,
  

•                                             signed long timeout,
  

•                                             uint32_t *idx)
  

+{

•   struct syncobj_wait_entry *entries;
  

•   struct dma_fence *fence;
  

•   signed long ret;
  

•   uint32_t signaled_count, i;
  

•   if (timeout == 0) {
  

•           signaled_count = 0;
  

•           for (i = 0; i < count; ++i) {
  

•                   ret = drm_syncobj_signaled(syncobjs[i], flags);
  

•                   if (ret < 0)
  

•                           return ret;
  

•                   if (ret == 0)
  

•                           continue;
  

•                   if (signaled_count == 0 && idx)
  

•                           *idx = i;
  

•                   signaled_count++;
  

•           }
  

•           if (flags & DRM_SYNCOBJ_WAIT_FLAGS_WAIT_ALL)
  

•                   return signaled_count == count ? 1 : 0;
  

•           else
  

•                   return signaled_count > 0 ? 1 : 0;
  

There's a very annoying laxness in the dma_fence API here, in that backends are not required to automatically report when a fence is signaled prior to fence->ops->enable_signaling() being called. So here if we fail to match signaled_count, we need to fallthough and try a 0 timeout wait!

Christian, dma_fence_wait_any_timeout() has this same bug you told me off for, e.g. commit 698c0f7ff216 ("dma-buf/fence: revert "don't wait when specified timeout is zero" (v2)")! -Chris