V4L2VDA: use YV12 as output format if processor supports it.

media/gpu/v4l2_video_decode_accelerator.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "media/gpu/v4l2_video_decode_accelerator.h"
 
 #include <dlfcn.h>
 #include <errno.h>
 #include <fcntl.h>
 #include <linux/videodev2.h>
@@ skipping 2020 matching lines @@
                   fmtdesc.pixelformat) != processor_input_formats.end()) {
       DVLOGF(1) << "Image processor input format=" << fmtdesc.pixelformat;
       return fmtdesc.pixelformat;
     }
     ++fmtdesc.index;
   }
   return 0;
 }
 
 uint32_t V4L2VideoDecodeAccelerator::FindImageProcessorOutputFormat() {
+  // Prefer YVU420 and NV12 because ArcGpuVideoDecodeAccelerator and drm_gralloc
+  // only support single physical plane. Prefer YVU420 over NV12 because chrome
+  // rendering supports YV12 only. When we use NV12, chrome thinks it is RGBA
+  // and mali handles that transparently knowing it is really NV12.
+  static const uint32_t kPreferredFormats[] = {V4L2_PIX_FMT_YVU420,
+                                               V4L2_PIX_FMT_NV12};
+  struct {

[kcwu, 2016/08/22 08:07:00]

I feel it's unnecessary to use struct. A normal function or even a lambda is
enough.

[wuchengli, 2016/08/22 09:08:04]

Yeah. Lambda is simpler. Done.

+    bool operator()(uint32_t a, uint32_t b) {
+      auto iter_a = std::find(std::begin(kPreferredFormats),
+                              std::end(kPreferredFormats), a);
+      auto iter_b = std::find(std::begin(kPreferredFormats),
+                              std::end(kPreferredFormats), b);
+      return iter_a < iter_b;
+    }
+  } preferred_formats_first;
+
   V4L2ImageProcessor image_processor(image_processor_device_);
   std::vector<uint32_t> processor_output_formats =
       image_processor.GetSupportedOutputFormats();
+
+  // Move the preferred format to the front.
+  std::sort(processor_output_formats.begin(), processor_output_formats.end(),

[kcwu, 2016/08/22 08:07:00]

Just curious, does the ordering of GetSupportedOutputFormats() output mean
something? I'm wondering should we try to keep original order if not in our
preference list?
If so, use stable_sort.

[wuchengli, 2016/08/22 09:08:03]

The order of GetSupportedOutputFormats does not mean anything. It's just the
order returned by the kernel driver. Also, the formats returned from
GetSupportedOutputFormats should not have duplicates.

+            preferred_formats_first);
+
   for (uint32_t processor_output_format : processor_output_formats) {
     if (device_->CanCreateEGLImageFrom(processor_output_format)) {
       DVLOGF(1) << "Image processor output format=" << processor_output_format;
       return processor_output_format;
     }
   }
 
   return 0;
 }
 
@@ skipping 217 matching lines @@
       Enqueue();
   }
 }
 
 void V4L2VideoDecodeAccelerator::ImageProcessorError() {
   LOGF(ERROR) << "Image processor error";
   NOTIFY_ERROR(PLATFORM_FAILURE);
 }
 
 }  // namespace media