V4L2VideoDecodeAccelerator: implement flush by VIDIOC_DECODER_CMD.

media/gpu/v4l2_video_decode_accelerator.cc

Index: media/gpu/v4l2_video_decode_accelerator.cc
diff --git a/media/gpu/v4l2_video_decode_accelerator.cc b/media/gpu/v4l2_video_decode_accelerator.cc
index b4ac8a19f993babcca1d4833d9a59ce3e83dc9e4..c68371df31c9cb66cbf185a1455c7f70dd45198c 100644
--- a/media/gpu/v4l2_video_decode_accelerator.cc
+++ b/media/gpu/v4l2_video_decode_accelerator.cc
@@ -164,6 +164,8 @@ V4L2VideoDecodeAccelerator::V4L2VideoDecodeAccelerator(
       decoder_decode_buffer_tasks_scheduled_(0),
       decoder_frames_at_client_(0),
       decoder_flushing_(false),
+      decoder_cmd_supported_(false),
+      flush_waiting_last_output_buffer_(false),
       reset_pending_(false),
       decoder_partial_frame_pending_(false),
       input_streamon_(false),
@@ -287,6 +289,8 @@ bool V4L2VideoDecodeAccelerator::Initialize(const Config& config,
     return false;
   }
 
+  decoder_cmd_supported_ = IsDecoderCmdSupported();
+
   decoder_state_ = kInitialized;
   output_mode_ = config.output_mode;
 
@@ -1393,6 +1397,17 @@ bool V4L2VideoDecodeAccelerator::DequeueOutputBuffer() {
       SendPictureReady();
       output_record.cleared = true;
     }
+    if ((dqbuf.flags & V4L2_BUF_FLAG_LAST)) {

[kcwu, 2016/10/12 02:32:39]

IIUC, according to
https://linuxtv.org/downloads/v4l-dvb-apis/vidioc-decoder-cmd.html, |bytesused|
may be zero (line 1374), then this line won't be reached.

[wuchengli, 2016/10/12 03:08:23]

Will fix this.

+      DVLOGF(3) << "Got last output buffer. Waiting last buffer="
+                << flush_waiting_last_output_buffer_;
+      if (flush_waiting_last_output_buffer_) {
+        struct v4l2_decoder_cmd cmd;
+        memset(&cmd, 0, sizeof(cmd));
+        cmd.cmd = V4L2_DEC_CMD_START;
+        IOCTL_OR_ERROR_RETURN_FALSE(VIDIOC_DECODER_CMD, &cmd);
+        flush_waiting_last_output_buffer_ = false;
+      }
+    }
   }
   return true;
 }
@@ -1544,12 +1559,21 @@ void V4L2VideoDecodeAccelerator::FlushTask() {
 
   // We don't support stacked flushing.
   DCHECK(!decoder_flushing_);
-
-  // Queue up an empty buffer -- this triggers the flush.
-  decoder_input_queue_.push(
-      linked_ptr<BitstreamBufferRef>(new BitstreamBufferRef(
-          decode_client_, decode_task_runner_, nullptr, kFlushBufferId)));
+  DCHECK(!flush_waiting_last_output_buffer_);
+  if (decoder_cmd_supported_) {
+    struct v4l2_decoder_cmd cmd;
+    memset(&cmd, 0, sizeof(cmd));
+    cmd.cmd = V4L2_DEC_CMD_STOP;
+    IOCTL_OR_ERROR_RETURN(VIDIOC_DECODER_CMD, &cmd);
+    flush_waiting_last_output_buffer_ = true;
+  } else {
+    // Queue up an empty buffer -- this triggers the flush.
+    decoder_input_queue_.push(
+        linked_ptr<BitstreamBufferRef>(new BitstreamBufferRef(
+            decode_client_, decode_task_runner_, nullptr, kFlushBufferId)));
+  }
   decoder_flushing_ = true;
+
   SendPictureReady();  // Send all pending PictureReady.
 
   ScheduleDecodeBufferTaskIfNeeded();
@@ -1557,8 +1581,10 @@ void V4L2VideoDecodeAccelerator::FlushTask() {
 
 void V4L2VideoDecodeAccelerator::NotifyFlushDoneIfNeeded() {
   DCHECK(decoder_thread_.task_runner()->BelongsToCurrentThread());
-  if (!decoder_flushing_)
+  if (!decoder_flushing_) {
+    DVLOGF(3) << "Not flushing";
     return;
+  }
 
   // Pipeline is empty when:
   // * Decoder input queue is empty of non-delayed buffers.
@@ -1568,15 +1594,25 @@ void V4L2VideoDecodeAccelerator::NotifyFlushDoneIfNeeded() {
   // * All image processor buffers are returned.
   if (!decoder_input_queue_.empty()) {
     if (decoder_input_queue_.front()->input_id !=
-        decoder_delay_bitstream_buffer_id_)
+        decoder_delay_bitstream_buffer_id_) {
+      DVLOGF(3) << "Some decoder inputs are not queued.";
       return;
+    }
   }
-  if (decoder_current_input_buffer_ != -1)
+  if (decoder_current_input_buffer_ != -1) {
+    DVLOGF(3) << "Current input buffer != -1";
     return;
-  if ((input_ready_queue_.size() + input_buffer_queued_count_) != 0)
+  }
+  if ((input_ready_queue_.size() + input_buffer_queued_count_) != 0) {
+    DVLOGF(3) << "some input buffers are not dequeued.";
     return;
+  }
   if (image_processor_bitstream_buffer_ids_.size() != 0)
     return;
+  if (flush_waiting_last_output_buffer_) {
+    DVLOGF(3) << "Waiting last output buffer";
+    return;
+  }
 
   // TODO(posciak): crbug.com/270039. Exynos requires a streamoff-streamon
   // sequence after flush to continue, even if we are not resetting. This would
@@ -1603,6 +1639,25 @@ void V4L2VideoDecodeAccelerator::NotifyFlushDoneIfNeeded() {
   ScheduleDecodeBufferTaskIfNeeded();
 }
 
+bool V4L2VideoDecodeAccelerator::IsDecoderCmdSupported() {
+  struct v4l2_decoder_cmd cmd;
+  memset(&cmd, 0, sizeof(cmd));
+  cmd.cmd = V4L2_DEC_CMD_START;
+  if (device_->Ioctl(VIDIOC_TRY_DECODER_CMD, &cmd) != 0) {
+    DVLOGF(3) "V4L2_DEC_CMD_START is not supported.";
+    return false;
+  }
+
+  memset(&cmd, 0, sizeof(cmd));
+  cmd.cmd = V4L2_DEC_CMD_STOP;
+  if (device_->Ioctl(VIDIOC_TRY_DECODER_CMD, &cmd) != 0) {
+    DVLOGF(3) "V4L2_DEC_CMD_STOP is not supported.";
+    return false;
+  }
+
+  return true;
+}
+
 void V4L2VideoDecodeAccelerator::ResetTask() {
   DVLOGF(3);
   DCHECK(decoder_thread_.task_runner()->BelongsToCurrentThread());
@@ -1722,6 +1777,7 @@ void V4L2VideoDecodeAccelerator::DestroyTask() {
   while (!decoder_input_queue_.empty())
     decoder_input_queue_.pop();
   decoder_flushing_ = false;
+  flush_waiting_last_output_buffer_ = false;
 
   if (image_processor_)
     image_processor_.release()->Destroy();
@@ -1785,6 +1841,9 @@ bool V4L2VideoDecodeAccelerator::StopOutputStream() {
   IOCTL_OR_ERROR_RETURN_FALSE(VIDIOC_STREAMOFF, &type);
   output_streamon_ = false;
 
+  // Output stream is stopped. No need to wait the buffer anymore.
+  flush_waiting_last_output_buffer_ = false;

[kcwu, 2016/10/12 02:32:39]

This line won't be executed if output_streamon_ is false.

IIUC, if the client calls
1. Initalize()
2. Flush() -> flush_waiting_last_output_buffer_ = true
3. not enqueue anything
4. Reset() -> flush_waiting_last_output_buffer_ not change

[wuchengli, 2016/10/12 03:08:23]

FlushTask won't set flush_waiting_last_output_buffer_ to true if the state is
kInitialized. I need to think what if the state is kResetting,
kChangingResolution, or kAwaitingPictureBuffers in FlushTask.

+
   for (size_t i = 0; i < output_buffer_map_.size(); ++i) {
     // After streamoff, the device drops ownership of all buffers, even if we
     // don't dequeue them explicitly. Some of them may still be owned by the