media/gpu/v4l2: Guard MT21Decompressor correctly

The MT21Decompressor was recently introduced for ChromeOS. This function
is written in NEON intrinisics and so is ARM specific. However references
to it added to V4L2VDA are not correctly guarded. This breaks the build
on Linux, on both ARM64 and x86_64.

Nothing limits the function to ChromeOS. A user running Chrome on an
MT8173 device running Linux could theoretically take advantage of it.
The implementation, due to its use of intrinsics, is still limited to
ARM.

Add guards around references to MT21Decompressor in V4L2VDA. Also
loosen the requirements so that it can be built on Linux.

Bug: b:284994884, b:258331312, b:291169645
Change-Id: Ib1164c2286735a3ebd30bd1cd53857d01234da74
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4710354
Commit-Queue: Chen-Yu Tsai <wenst@chromium.org>
Reviewed-by: Justin Green <greenjustin@google.com>
Reviewed-by: Miguel Casas-Sanchez <mcasas@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1175283}

media/gpu/v4l2/BUILD.gn

@@ -64,6 +64,14 @@ source_set("v4l2") {
     ]
   }
 
+  if (current_cpu == "arm" || current_cpu == "arm64") {
+    sources += [
+      "mt21/mt21_decompressor.cc",
+      "mt21/mt21_decompressor.h",
+      "mt21/mt21_util.h",
+    ]
+  }
+
   if (is_chromeos) {
     sources += [
       # AV1 delegate depends on header files only in ChromeOS SDK
@@ -75,14 +83,6 @@ source_set("v4l2") {
       "v4l2_video_encode_accelerator.cc",
       "v4l2_video_encode_accelerator.h",
     ]
-
-    if (current_cpu == "arm" || current_cpu == "arm64") {
-      sources += [
-        "mt21/mt21_decompressor.cc",
-        "mt21/mt21_decompressor.h",
-        "mt21/mt21_util.h",
-      ]
-    }
   }
 
   libs = [
@@ -224,7 +224,7 @@ test("v4l2_unittest") {
   ]
 }
 
-if (is_chromeos && (current_cpu == "arm" || current_cpu == "arm64")) {
+if (current_cpu == "arm" || current_cpu == "arm64") {
   test("mt21_util_unittest") {
     testonly = true
     sources = [

media/gpu/v4l2/legacy/v4l2_video_decode_accelerator.cc

@@ -413,18 +413,22 @@ void V4L2VideoDecodeAccelerator::AssignPictureBuffersTask(
     return;
   }
 
+  const bool prefer_software_mt21 =
+#ifdef SUPPORT_MT21_PIXEL_FORMAT_SOFTWARE_DECOMPRESSION
+      base::FeatureList::IsEnabled(media::kPreferSoftwareMT21);
+#else
+      false;
+#endif
   enum v4l2_memory memory;
-  if (!image_processor_device_ &&
-      !base::FeatureList::IsEnabled(media::kPreferSoftwareMT21) &&
+  if (!image_processor_device_ && !prefer_software_mt21 &&
       output_mode_ == Config::OutputMode::IMPORT) {
     memory = V4L2_MEMORY_DMABUF;
   } else {
     memory = V4L2_MEMORY_MMAP;
   }
 
-  if (output_queue_->AllocateBuffers(
-          buffers.size(), memory,
-          base::FeatureList::IsEnabled(media::kPreferSoftwareMT21)) == 0) {
+  if (output_queue_->AllocateBuffers(buffers.size(), memory,
+                                     prefer_software_mt21) == 0) {
     LOG(ERROR) << "Failed to request buffers!";
     NOTIFY_ERROR(PLATFORM_FAILURE);
     return;
@@ -573,7 +577,11 @@ void V4L2VideoDecodeAccelerator::AssignEGLImage(size_t buffer_index,
 
   // Make ourselves available if CreateEGLImageFor has been called from
   // ImportBufferForPictureTask.
-  if (!image_processor_ && !mt21_decompressor_) {
+  if (!image_processor_
+#ifdef SUPPORT_MT21_PIXEL_FORMAT_SOFTWARE_DECOMPRESSION
+      && !mt21_decompressor_
+#endif
+  ) {
     DCHECK_EQ(output_wait_map_.count(picture_buffer_id), 1u);
     output_wait_map_.erase(picture_buffer_id);
     if (decoder_state_ != kChangingResolution) {
@@ -677,16 +685,22 @@ void V4L2VideoDecodeAccelerator::ImportBufferForPictureTask(
     }
     DCHECK_EQ(egl_image_size_, handle_size);
 
+#ifdef SUPPORT_MT21_PIXEL_FORMAT_SOFTWARE_DECOMPRESSION
     if (base::FeatureList::IsEnabled(media::kPreferSoftwareMT21) &&
         !mt21_decompressor_) {
       mt21_decompressor_ = std::make_unique<MT21Decompressor>(coded_size_);
     }
+#endif
 
     // For allocate mode, the IP will already have been created in
     // AssignPictureBuffersTask.
     // Note: usage of the MT21 software decompressor disables the image
     // processor.
-    if (image_processor_device_ && !image_processor_ && !mt21_decompressor_) {
+    if (image_processor_device_ && !image_processor_
+#ifdef SUPPORT_MT21_PIXEL_FORMAT_SOFTWARE_DECOMPRESSION
+        && !mt21_decompressor_
+#endif
+    ) {
       DCHECK_EQ(kAwaitingPictureBuffers, decoder_state_);
       // This is the first buffer import. Create the image processor and change
       // the decoder state. The client may adjust the coded width. We don't have
@@ -752,7 +766,11 @@ void V4L2VideoDecodeAccelerator::ImportBufferForPictureTask(
     // time since we already have its DMABUF fds. It is guaranteed that
     // CreateEGLImageFor will run before the picture is passed to the client
     // because the picture will need to be cleared on the child thread first.
-    if (!image_processor_ && !mt21_decompressor_) {
+    if (!image_processor_
+#ifdef SUPPORT_MT21_PIXEL_FORMAT_SOFTWARE_DECOMPRESSION
+        && !mt21_decompressor_
+#endif
+    ) {
       DCHECK_GT(handle.planes.size(), 0u);
       size_t index = iter - output_buffer_map_.begin();
 
@@ -1513,7 +1531,11 @@ bool V4L2VideoDecodeAccelerator::DequeueOutputBuffer() {
     DCHECK_GE(bitstream_buffer_id, 0);
     DVLOGF(4) << "Dequeue output buffer: dqbuf index=" << buf->BufferId()
               << " bitstream input_id=" << bitstream_buffer_id;
-    if (image_processor_device_ || mt21_decompressor_) {
+    if (image_processor_device_
+#ifdef SUPPORT_MT21_PIXEL_FORMAT_SOFTWARE_DECOMPRESSION
+        || mt21_decompressor_
+#endif
+    ) {
       if (!ProcessFrame(bitstream_buffer_id, buf)) {
         LOG(ERROR) << "Processing frame failed";
         NOTIFY_ERROR(PLATFORM_FAILURE);
@@ -1896,7 +1918,10 @@ void V4L2VideoDecodeAccelerator::DestroyTask() {
   image_processor_ = nullptr;
   while (!buffers_at_ip_.empty())
     buffers_at_ip_.pop();
+
+#ifdef SUPPORT_MT21_PIXEL_FORMAT_SOFTWARE_DECOMPRESSION
   mt21_decompressor_ = nullptr;
+#endif
 
   DestroyInputBuffers();
   DestroyOutputBuffers();
@@ -2025,7 +2050,10 @@ void V4L2VideoDecodeAccelerator::StartResolutionChange() {
   buffers_at_client_.clear();
 
   image_processor_ = nullptr;
+
+#ifdef SUPPORT_MT21_PIXEL_FORMAT_SOFTWARE_DECOMPRESSION
   mt21_decompressor_ = nullptr;
+#endif
 
   if (!DestroyOutputBuffers()) {
     LOG(ERROR) << "Failed destroying output buffers.";
@@ -2305,10 +2333,14 @@ bool V4L2VideoDecodeAccelerator::SetupFormats() {
   DCHECK(!image_processor_device_);
   if (!output_format_fourcc_) {
     VLOGF(2) << "Could not find a usable output format. Try image processor";
+#ifdef SUPPORT_MT21_PIXEL_FORMAT_SOFTWARE_DECOMPRESSION
     if (base::FeatureList::IsEnabled(media::kPreferSoftwareMT21)) {
       output_format_fourcc_ = Fourcc(Fourcc::MT21);
       egl_image_format_fourcc_ = Fourcc(Fourcc::NV12);
     } else {
+#else
+    {
+#endif
       if (!V4L2ImageProcessorBackend::IsSupported()) {
         VLOGF(1) << "Image processor not available";
         return false;
@@ -2402,6 +2434,7 @@ bool V4L2VideoDecodeAccelerator::ProcessFrame(int32_t bitstream_buffer_id,
   // Keep reference to the IP input until the frame is processed
   buffers_at_ip_.push(std::make_pair(bitstream_buffer_id, buf));
 
+#ifdef SUPPORT_MT21_PIXEL_FORMAT_SOFTWARE_DECOMPRESSION
   if (base::FeatureList::IsEnabled(media::kPreferSoftwareMT21)) {
     if (!mt21_decompressor_) {
       LOG(ERROR) << "PreferSoftwareMT21 enabled, but MT21 decompressor was not "
@@ -2457,6 +2490,7 @@ bool V4L2VideoDecodeAccelerator::ProcessFrame(int32_t bitstream_buffer_id,
 
     return true;
   }
+#endif
 
   scoped_refptr<VideoFrame> input_frame = buf->GetVideoFrame();
   if (!input_frame) {

media/gpu/v4l2/legacy/v4l2_video_decode_accelerator.h

@@ -18,6 +18,14 @@
 #include <utility>
 #include <vector>
 
+#include "build/build_config.h"
+
+#if defined(ARCH_CPU_ARM_FAMILY)
+// The MT21C software decompressor is tightly coupled to the MT8173.
+// See mt21_decompressor.h
+#define SUPPORT_MT21_PIXEL_FORMAT_SOFTWARE_DECOMPRESSION
+#endif
+
 #include "base/cancelable_callback.h"
 #include "base/containers/queue.h"
 #include "base/functional/callback_forward.h"
@@ -32,7 +40,9 @@
 #include "media/gpu/chromeos/image_processor.h"
 #include "media/gpu/gpu_video_decode_accelerator_helpers.h"
 #include "media/gpu/media_gpu_export.h"
+#ifdef SUPPORT_MT21_PIXEL_FORMAT_SOFTWARE_DECOMPRESSION
 #include "media/gpu/v4l2/mt21/mt21_decompressor.h"
+#endif
 #include "media/gpu/v4l2/v4l2_device.h"
 #include "media/video/picture.h"
 #include "media/video/video_decode_accelerator.h"
@@ -616,7 +626,9 @@ class MEDIA_GPU_EXPORT V4L2VideoDecodeAccelerator
   // Image processor. Accessed on |decoder_thread_|.
   std::unique_ptr<ImageProcessor> image_processor_;
 
+#ifdef SUPPORT_MT21_PIXEL_FORMAT_SOFTWARE_DECOMPRESSION
   std::unique_ptr<MT21Decompressor> mt21_decompressor_;
+#endif
 
   // The format of EGLImage.
   absl::optional<Fourcc> egl_image_format_fourcc_;

media/gpu/v4l2/mt21/mt21_decompressor.cc

@@ -2,15 +2,11 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#include "media/gpu/v4l2/mt21/mt21_decompressor.h"
-
-#if BUILDFLAG(IS_CHROMEOS) && defined(ARCH_CPU_ARM_FAMILY) && \
-    (defined(COMPILER_GCC) || defined(__clang__))
-
 #include <sched.h>
 #include <stdlib.h>
 
 #include "base/bits.h"
+#include "media/gpu/v4l2/mt21/mt21_decompressor.h"
 #include "media/gpu/v4l2/mt21/mt21_util.h"
 #include "third_party/libyuv/include/libyuv/planar_functions.h"
 
@@ -249,5 +245,3 @@ void MT21Decompressor::MT21ToNV12(const uint8_t* src_y,
 }
 
 }  // namespace media
-
-#endif

media/gpu/v4l2/mt21/mt21_decompressor.h

@@ -22,8 +22,13 @@
 
 #include "build/build_config.h"
 
-#if BUILDFLAG(IS_CHROMEOS) && defined(ARCH_CPU_ARM_FAMILY) && \
-    (defined(COMPILER_GCC) || defined(__clang__))
+#if !defined(ARCH_CPU_ARM_FAMILY)
+#error "MT21Decompressor is only intended to run on MT8173 (ARM)"
+#endif
+
+#if !(defined(COMPILER_GCC) || defined(__clang__))
+#error "MT21Decompressor is only intended to be built with GCC or Clang"
+#endif
 
 #include <stdint.h>
 
@@ -117,6 +122,4 @@ class MT21Decompressor {
 
 }  // namespace media
 
-#endif
-
 #endif  // MEDIA_GPU_V4L2_MT21_MT21_DECOMPRESSOR_H_

media/gpu/v4l2/mt21/mt21_util.h

@@ -23,8 +23,13 @@
 
 #include "build/build_config.h"
 
-#if BUILDFLAG(IS_CHROMEOS) && defined(ARCH_CPU_ARM_FAMILY) && \
-    (defined(COMPILER_GCC) || defined(__clang__))
+#if !defined(ARCH_CPU_ARM_FAMILY)
+#error "MT21Decompressor is only intended to run on MT8173 (ARM)"
+#endif
+
+#if !(defined(COMPILER_GCC) || defined(__clang__))
+#error "MT21Decompressor is only intended to be built with GCC or Clang"
+#endif
 
 #include <arm_neon.h>
 #include <stdint.h>
@@ -1115,6 +1120,4 @@ void BinSubblocks(const uint8_t* src,
 
 }  // namespace media
 
-#endif
-
 #endif  // MEDIA_GPU_V4L2_MT21_MT21_UTIL_H_