If all the sync points were signaled in both fences a and b, there was only one sync point in merged fence which is a_fence[0]. The Fence structure in android framework might be confused about timestamp if there were any sync points which were signaled after a_fence[0]. It might be more reasonable to use timestamp of last signaled sync point to represent the merged fence. The issue can be found from EGL extension ANDROID_get_frame_timestamps. Sometimes the return value of EGL_READS_DONE_TIME_ANDROID is head of the return value of EGL_RENDERING_COMPLETE_TIME_ANDROID. That means display/composition had been completed before rendering was completed that is incorrect. Some discussion can be found at: https://android-review.googlesource.com/c/kernel/common/+/907009 Signed-off-by: Michael Yang <michael.yang@xxxxxxxxxx> --- Hi, I didn't get response since I previously sent this a month ago. Could someone have a chance to look at it please? Thanks. drivers/dma-buf/sync_file.c | 25 +++++++++++++++++++++++-- 1 file changed, 23 insertions(+), 2 deletions(-) diff --git a/drivers/dma-buf/sync_file.c b/drivers/dma-buf/sync_file.c index 4f6305c..d46bfe1 100644 --- a/drivers/dma-buf/sync_file.c +++ b/drivers/dma-buf/sync_file.c @@ -274,8 +274,29 @@ static struct sync_file *sync_file_merge(const char *name, struct sync_file *a, for (; i_b < b_num_fences; i_b++) add_fence(fences, &i, b_fences[i_b]); - if (i == 0) - fences[i++] = dma_fence_get(a_fences[0]); + /* If all the sync pts were signaled, then adding the sync_pt who + * was the last signaled to the fence. + */ + if (i == 0) { + struct dma_fence *last_signaled_sync_pt = a_fences[0]; + int iter; + + for (iter = 1; iter < a_num_fences; iter++) { + if (ktime_compare(last_signaled_sync_pt->timestamp, + a_fences[iter]->timestamp) < 0) { + last_signaled_sync_pt = a_fences[iter]; + } + } + + for (iter = 0; iter < b_num_fences; iter++) { + if (ktime_compare(last_signaled_sync_pt->timestamp, + b_fences[iter]->timestamp) < 0) { + last_signaled_sync_pt = b_fences[iter]; + } + } + + fences[i++] = dma_fence_get(last_signaled_sync_pt); + } if (num_fences > i) { nfences = krealloc(fences, i * sizeof(*fences), -- 2.7.4
