src/media/drivers/amlogic_decoder/h264_decoder.cc

// Copyright 2018 The Fuchsia 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 "h264_decoder.h"

#include <lib/media/codec_impl/codec_buffer.h>
#include <lib/media/codec_impl/codec_frame.h>
#include <lib/media/codec_impl/codec_packet.h>
#include <lib/trace/event.h>
#include <lib/zx/vmo.h>

#include <fbl/algorithm.h>

#include "firmware_blob.h"
#include "macros.h"
#include "memory_barriers.h"
#include "pts_manager.h"
#include "util.h"

// TODO(35200):
//
// Change these to InternalBuffer:
//
// InputContext::buffer - optionally secure
// (done) reference_mv_buffer_ - optionally secure
// (done) codec_data_ - optionally secure
// (done) sei_data_buffer_ - optionally secure
//
// Plumb is_secure to each of the above.
//
// (Fine as io_bufer_t for now:
//    * loading firmware uses video_firmware TA when possible, so io_buffer_t when
//      !is_tee_available_ is fine.
//    * secondary_firmware_ - same as for main firmware.

static const uint32_t kBufferAlignShift = 4 + 12;
static const uint32_t kBufferAlign = 1 << kBufferAlignShift;
constexpr uint32_t kMaxActualDPBSize = 24;

// AvScratch1
class StreamInfo : public TypedRegisterBase<DosRegisterIo, StreamInfo, uint32_t> {
 public:
  DEF_FIELD(7, 0, width_in_mbs);
  DEF_FIELD(23, 8, total_mbs);
  DEF_FIELD(30, 24, max_reference_size);
  DEF_BIT(31, mv_size_flag);

  static auto Get() { return AddrType(0x09c1 * 4); }
};

// AvScratch2
class SequenceInfo : public TypedRegisterBase<DosRegisterIo, SequenceInfo, uint32_t> {
 public:
  DEF_BIT(0, aspect_ratio_info_present_flag);
  DEF_BIT(1, timing_info_present_flag);
  DEF_BIT(4, pic_struct_present_flag);

  // relatively lower-confidence vs. other bits - not confirmed
  DEF_BIT(6, fixed_frame_rate_flag);

  DEF_FIELD(14, 13, chroma_format_idc);
  DEF_BIT(15, frame_mbs_only_flag);
  DEF_FIELD(23, 16, aspect_ratio_idc);

  static auto Get() { return AddrType(0x09c2 * 4); }
};

// AvScratch3
class SampleAspectRatioInfo
    : public TypedRegisterBase<DosRegisterIo, SampleAspectRatioInfo, uint32_t> {
 public:
  DEF_FIELD(15, 0, sar_width);
  DEF_FIELD(31, 16, sar_height);

  static auto Get() { return AddrType(0x09c3 * 4); }
};

// AvScratch6
class CropInfo : public TypedRegisterBase<DosRegisterIo, CropInfo, uint32_t> {
 public:
  // All quantities are the number of pixels to be cropped from each side.
  DEF_FIELD(7, 0, bottom);
  DEF_FIELD(15, 8, top);  // Ignored
  DEF_FIELD(23, 16, right);
  DEF_FIELD(31, 24, left);  // Ignored

  static auto Get() { return AddrType(0x09c6 * 4); }
};

// AvScratchF
class CodecSettings : public TypedRegisterBase<DosRegisterIo, CodecSettings, uint32_t> {
 public:
  DEF_BIT(1, trickmode_i);
  DEF_BIT(2, zeroed0);
  DEF_BIT(3, drop_b_frames);
  DEF_BIT(4, error_recovery_mode);
  DEF_BIT(5, zeroed1);
  DEF_BIT(6, ip_frames_only);
  DEF_BIT(7, disable_fast_poc);

  static auto Get() { return AddrType(0x09cf * 4); }
};

// AvScratchInfo1+
class PicInfo : public TypedRegisterBase<DosRegisterIo, PicInfo, uint32_t> {
 public:
  DEF_FIELD(4, 0, buffer_index);
  DEF_BIT(9, error);
  DEF_BIT(15, eos);
  DEF_FIELD(31, 16, stream_offset);

  static auto Get(uint32_t i) { return AddrType((0x09c1 + i) * 4); }
};

// 0 means "Unspecified"
constexpr uint32_t kAspectRatioIdcExtendedSar = 255;

// This struct type doesn't need a name, since we only read this one static
// instance.
struct {
  const uint8_t sar_width;
  const uint8_t sar_height;
} kSarTable[] = {
    // 0 - entry 0 in this table is never read, but it's only 2 bytes so we just
    // let it exist since subtracting 1 from aspect_ratio_idc would probably
    // take
    // ~2 code bytes or more anyway.
    {0, 0},
    // 1
    {1, 1},
    // 2
    {12, 11},
    // 3
    {10, 11},
    // 4
    {16, 11},
    // 5
    {40, 33},
    // 6
    {24, 11},
    // 7
    {20, 11},
    // 8
    {32, 11},
    // 9
    {80, 33},
    // 10
    {18, 11},
    // 11
    {15, 11},
    // 12
    {64, 33},
    // 13
    {160, 99},
    // 14
    {4, 3},
    // 15
    {3, 2},
    // 16
    {2, 1},
};

static uint32_t GetMaxDpbSize(uint32_t level_idc, uint32_t width_in_mbs, uint32_t height_in_mbs) {
  // From Table A-1 of the h.264 spec.
  // https://www.itu.int/rec/T-REC-H.264-201704-I/en
  uint32_t max_dpb_mbs;
  switch (level_idc) {
    case 10:
      max_dpb_mbs = 396;
      break;
    case 11:
      max_dpb_mbs = 900;
      break;
    case 12:
    case 13:
    case 20:
      max_dpb_mbs = 2376;
      break;
    case 21:
      max_dpb_mbs = 4752;
      break;
    case 22:
    case 30:
      max_dpb_mbs = 8100;
      break;
    case 31:
      max_dpb_mbs = 18000;
      break;
    case 32:
      max_dpb_mbs = 20480;
      break;
    case 40:
    case 41:
      max_dpb_mbs = 32768;
      break;
    case 42:
      max_dpb_mbs = 34816;
      break;
    case 50:
      max_dpb_mbs = 110400;
      break;
    case 51:
    case 52:
      max_dpb_mbs = 184320;
      break;
    case 60:
    case 61:
    case 62:
      max_dpb_mbs = 696320;
      break;
    default:
      return 0;
  }

  uint32_t num_mbs = width_in_mbs * height_in_mbs;
  if (!num_mbs)
    return 0;
  return std::min(16u, (max_dpb_mbs + num_mbs - 1) / num_mbs);
}

H264Decoder::~H264Decoder() {
  owner_->core()->StopDecoding();
  owner_->core()->WaitForIdle();
  BarrierBeforeRelease();
  io_buffer_release(&secondary_firmware_);
  // ~reference_mv_buffer_
  // ~sei_data_buffer_
  // ~codec_data_
}

zx_status_t H264Decoder::ResetHardware() {
  DosSwReset0::Get().FromValue((1 << 7) | (1 << 6) | (1 << 4)).WriteTo(owner_->dosbus());
  DosSwReset0::Get().FromValue(0).WriteTo(owner_->dosbus());

  // Reads are used for delaying running later code.
  for (uint32_t i = 0; i < 3; i++) {
    DosSwReset0::Get().ReadFrom(owner_->dosbus());
  }

  DosSwReset0::Get().FromValue((1 << 7) | (1 << 6) | (1 << 4)).WriteTo(owner_->dosbus());
  DosSwReset0::Get().FromValue(0).WriteTo(owner_->dosbus());

  DosSwReset0::Get().FromValue((1 << 9) | (1 << 8)).WriteTo(owner_->dosbus());
  DosSwReset0::Get().FromValue(0).WriteTo(owner_->dosbus());

  // Reads are used for delaying running later code.
  for (uint32_t i = 0; i < 3; i++) {
    DosSwReset0::Get().ReadFrom(owner_->dosbus());
  }

  auto temp = PowerCtlVld::Get().ReadFrom(owner_->dosbus());
  temp.set_reg_value(temp.reg_value() | (1 << 9) | (1 << 6));
  temp.WriteTo(owner_->dosbus());

  return ZX_OK;
}

zx_status_t H264Decoder::LoadSecondaryFirmware(const uint8_t* data, uint32_t firmware_size) {
  // For some reason, some portions of the firmware aren't loaded into the
  // hardware directly, but are kept in main memory.
  constexpr uint32_t kSecondaryFirmwareSize = 4 * 1024;
  constexpr uint32_t kSecondaryFirmwareBufferSize = kSecondaryFirmwareSize * 5;
  {
    zx_status_t status = io_buffer_init_aligned(&secondary_firmware_, owner_->bti()->get(),
                                                kSecondaryFirmwareBufferSize, kBufferAlignShift,
                                                IO_BUFFER_RW | IO_BUFFER_CONTIG);
    if (status != ZX_OK) {
      DECODE_ERROR("Failed to make second firmware buffer: %d", status);
      return status;
    }
    SetIoBufferName(&secondary_firmware_, "H264SecondaryFirmware");

    auto addr = static_cast<uint8_t*>(io_buffer_virt(&secondary_firmware_));
    // The secondary firmware is in a different order in the file than the main
    // firmware expects it to have.
    memcpy(addr + 0, data + 0x4000, kSecondaryFirmwareSize);       // header
    memcpy(addr + 0x1000, data + 0x2000, kSecondaryFirmwareSize);  // data
    memcpy(addr + 0x2000, data + 0x6000, kSecondaryFirmwareSize);  // mmc
    memcpy(addr + 0x3000, data + 0x3000, kSecondaryFirmwareSize);  // list
    memcpy(addr + 0x4000, data + 0x5000, kSecondaryFirmwareSize);  // slice
  }
  io_buffer_cache_flush(&secondary_firmware_, 0, kSecondaryFirmwareBufferSize);
  return ZX_OK;
}

zx_status_t H264Decoder::Initialize() {
  uint8_t* data;
  uint32_t firmware_size;
  zx_status_t status =
      owner_->SetProtected(VideoDecoder::Owner::ProtectableHardwareUnit::kVdec, is_secure_);
  if (status != ZX_OK)
    return status;

  if (owner_->is_tee_available()) {
    status = owner_->TeeSmcLoadVideoFirmware(FirmwareBlob::FirmwareType::kDec_H264,
                                             FirmwareBlob::FirmwareVdecLoadMode::kCompatible);
    if (status != ZX_OK) {
      LOG(ERROR, "owner_->TeeSmcLoadVideoFirmware() failed - status: %d", status);
      return status;
    }
  } else {
    status = owner_->firmware_blob()->GetFirmwareData(FirmwareBlob::FirmwareType::kDec_H264, &data,
                                                      &firmware_size);
    if (status != ZX_OK)
      return status;
    status = owner_->core()->LoadFirmware(data, firmware_size);
    if (status != ZX_OK)
      return status;

    status = LoadSecondaryFirmware(data, firmware_size);
    if (status != ZX_OK)
      return status;
    BarrierAfterFlush();  // After secondary_firmware_ cache is flushed to RAM.

    AvScratchG::Get()
        .FromValue(truncate_to_32(io_buffer_phys(&secondary_firmware_)))
        .WriteTo(owner_->dosbus());
  }

  if (!WaitForRegister(std::chrono::milliseconds(100), [this]() {
        return !(DcacDmaCtrl::Get().ReadFrom(owner_->dosbus()).reg_value() & 0x8000);
      })) {
    DECODE_ERROR("Waiting for DCAC DMA timed out");
    return ZX_ERR_TIMED_OUT;
  }

  if (!WaitForRegister(std::chrono::milliseconds(100), [this]() {
        return !(LmemDmaCtrl::Get().ReadFrom(owner_->dosbus()).reg_value() & 0x8000);
      })) {
    DECODE_ERROR("Waiting for LMEM DMA timed out");
    return ZX_ERR_TIMED_OUT;
  }

  status = ResetHardware();
  if (status != ZX_OK)
    return status;

  PscaleCtrl::Get().FromValue(0).WriteTo(owner_->dosbus());
  AvScratch0::Get().FromValue(0).WriteTo(owner_->dosbus());

  // TODO(34192): After sysmem has min_base_phys_address_divisor, use that to avoid over-allocating
  // and rounding up here.
  const uint32_t kCodecDataSize = 0x1ee000 + kBufferAlign;
  auto codec_data_create_result = InternalBuffer::Create(
      "H264CodecData", &owner_->SysmemAllocatorSyncPtr(), owner_->bti(), kCodecDataSize, is_secure_,
      /*is_writable=*/true, /*is_mapping_needed*/ false);
  if (!codec_data_create_result.is_ok()) {
    LOG(ERROR, "Failed to make codec data buffer - status: %d", codec_data_create_result.error());
    return codec_data_create_result.error();
  }
  codec_data_.emplace(codec_data_create_result.take_value());
  zx_paddr_t aligned_codec_data_phys = fbl::round_up(codec_data_->phys_base(), kBufferAlign);
  // sysmem ensures that newly allocated buffers are zeroed and flushed, to extent possible, so
  // codec_data_ doesn't need CacheFlush() here.

  enum {
    kBufferStartAddressOffset = 0x1000000,
  };

  // This may wrap if the address is less than the buffer start offset.
  uint32_t buffer_offset = truncate_to_32(aligned_codec_data_phys) - kBufferStartAddressOffset;
  AvScratch1::Get().FromValue(buffer_offset).WriteTo(owner_->dosbus());

  AvScratch7::Get().FromValue(0).WriteTo(owner_->dosbus());
  AvScratch8::Get().FromValue(0).WriteTo(owner_->dosbus());
  AvScratch9::Get().FromValue(0).WriteTo(owner_->dosbus());
  VdecAssistMbox1ClrReg::Get().FromValue(1).WriteTo(owner_->dosbus());
  VdecAssistMbox1Mask::Get().FromValue(1).WriteTo(owner_->dosbus());
  MdecPicDcCtrl::Get().ReadFrom(owner_->dosbus()).set_nv12_output(true).WriteTo(owner_->dosbus());
  CodecSettings::Get()
      .ReadFrom(owner_->dosbus())
      .set_zeroed0(0)
      .set_drop_b_frames(false)
      .set_error_recovery_mode(1)
      .set_zeroed1(0)
      .set_ip_frames_only(0)
      .set_disable_fast_poc(0)
      .WriteTo(owner_->dosbus());

  // TODO(34192): After sysmem has min_base_phys_address_divisor, use that to avoid over-allocating
  // and rounding up here.
  constexpr uint32_t kSeiBufferSize = 8 * 1024 + kBufferAlign;
  // Sei data buffer must be readable from CPU (though we don't actually use it
  // yet).
  auto sei_create_result = InternalBuffer::Create("H264SeiData", &owner_->SysmemAllocatorSyncPtr(),
                                                  owner_->bti(), kSeiBufferSize, false,
                                                  /*is_writable=*/true, /*is_mapping_neede=*/false);
  if (!sei_create_result.is_ok()) {
    LOG(ERROR, "Failed to make sei data buffer - status: %d", sei_create_result.error());
    return sei_create_result.error();
  }
  sei_data_buffer_.emplace(sei_create_result.take_value());
  zx_paddr_t sei_data_buffer_aligned_phys =
      fbl::round_up(sei_data_buffer_->phys_base(), kBufferAlign);
  // Sysmem has zeroed sei_data_buffer_, flushed the zeroes, and fenced the flush, to extent
  // possible.

  AvScratchI::Get()
      .FromValue(truncate_to_32(sei_data_buffer_aligned_phys) - buffer_offset)
      .WriteTo(owner_->dosbus());
  AvScratchJ::Get().FromValue(0).WriteTo(owner_->dosbus());
  MdecPicDcThresh::Get().FromValue(0x404038aa).WriteTo(owner_->dosbus());

  owner_->core()->StartDecoding();
  return ZX_OK;
}

void H264Decoder::InitializedFrames(std::vector<CodecFrame> frames, uint32_t coded_width,
                                    uint32_t coded_height, uint32_t stride) {
  ZX_DEBUG_ASSERT(state_ == DecoderState::kWaitingForNewFrames);
  ZX_DEBUG_ASSERT(coded_width == stride);
  uint32_t frame_count = frames.size();
  for (uint32_t i = 0; i < frame_count; ++i) {
    auto frame = std::make_shared<VideoFrame>();
    // While we'd like to pass in IO_BUFFER_CONTIG, since we know the VMO was
    // allocated with zx_vmo_create_contiguous(), the io_buffer_init_vmo()
    // treats that flag as an invalid argument, so instead we have to pretend as
    // if it's a non-contiguous VMO, then validate that the VMO is actually
    // contiguous later in aml_canvas_config() called by
    // owner_->ConfigureCanvas() below.
    assert(frames[i].codec_buffer_spec.has_data());
    assert(frames[i].codec_buffer_spec.data().is_vmo());
    assert(frames[i].codec_buffer_spec.data().vmo().has_vmo_handle());
    zx_status_t status = io_buffer_init_vmo(
        &frame->buffer, owner_->bti()->get(),
        frames[i].codec_buffer_spec.data().vmo().vmo_handle().get(), 0, IO_BUFFER_RW);
    if (status != ZX_OK) {
      LOG(ERROR, "Failed to io_buffer_init_vmo() for frame - status: %d", status);
      OnFatalError();
      return;
    }
    io_buffer_cache_flush(&frame->buffer, 0, io_buffer_size(&frame->buffer, 0));

    BarrierAfterFlush();

    frame->hw_width = coded_width;
    frame->hw_height = coded_height;
    frame->coded_width = coded_width;
    frame->coded_height = coded_height;
    frame->stride = stride;
    frame->uv_plane_offset = stride * coded_height;
    frame->display_width = display_width_;
    frame->display_height = display_height_;
    frame->index = i;

    // can be nullptr
    frame->codec_buffer = frames[i].codec_buffer_ptr;
    if (frames[i].codec_buffer_ptr) {
      frames[i].codec_buffer_ptr->SetVideoFrame(frame);
    }

    // The ConfigureCanvas() calls validate that the VMO is physically
    // contiguous, regardless of how the VMO was created.
    auto y_canvas =
        owner_->ConfigureCanvas(&frame->buffer, 0, frame->stride, frame->coded_height, 0, 0);
    auto uv_canvas = owner_->ConfigureCanvas(&frame->buffer, frame->uv_plane_offset, frame->stride,
                                             frame->coded_height / 2, 0, 0);
    if (!y_canvas || !uv_canvas) {
      LOG(ERROR, "!y_canvas || !uv_canvas");
      OnFatalError();
      return;
    }

    AncNCanvasAddr::Get(i)
        .FromValue((uv_canvas->index() << 16) | (uv_canvas->index() << 8) | (y_canvas->index()))
        .WriteTo(owner_->dosbus());
    video_frames_.push_back({std::move(frame), std::move(y_canvas), std::move(uv_canvas)});
  }

  uint32_t actual_dpb_size = frame_count;
  ZX_DEBUG_ASSERT(actual_dpb_size <= kMaxActualDPBSize);
  ZX_DEBUG_ASSERT(next_mv_buffer_count_ <= next_max_dpb_size_ + 1);
  uint32_t av_scratch0 =
      (next_mv_buffer_count_ << 24) | (actual_dpb_size << 16) | (next_max_dpb_size_ << 8);
  AvScratch0::Get().FromValue(av_scratch0).WriteTo(owner_->dosbus());

  state_ = DecoderState::kRunning;
}

zx_status_t H264Decoder::InitializeFrames(uint32_t min_frame_count, uint32_t max_frame_count,
                                          uint32_t coded_width, uint32_t coded_height,
                                          uint32_t display_width, uint32_t display_height,
                                          bool has_sar, uint32_t sar_width, uint32_t sar_height) {
  DLOG("InitializeFrames() display_width: %u display_height: %u", display_width, display_height);
  video_frames_.clear();
  returned_frames_.clear();

  uint32_t stride = coded_width;
  display_width_ = display_width;
  display_height_ = display_height;

  // Regardless of local allocation of VMOs or remote allocation of VMOs, we
  // first represent the frames this way.  This representation conveys the
  // potentially-non-zero offset into the VMO, and allows sharing code further
  // down.
  std::vector<CodecFrame> frames;
  ::zx::bti duplicated_bti;
  zx_status_t dup_result = owner_->bti()->duplicate(ZX_RIGHT_SAME_RIGHTS, &duplicated_bti);
  if (dup_result != ZX_OK) {
    DECODE_ERROR("Failed to duplicate BTI - status: %d", dup_result);
    return dup_result;
  }
  zx_status_t initialize_result = client_->InitializeFrames(
      std::move(duplicated_bti), min_frame_count, max_frame_count, coded_width, coded_height,
      stride, display_width, display_height, has_sar, sar_width, sar_height);
  if (initialize_result != ZX_OK) {
    if (initialize_result != ZX_ERR_STOP) {
      DECODE_ERROR("initialize_frames_handler_() failed - status: %d", initialize_result);
    }
    return initialize_result;
  }

  return ZX_OK;
}

void H264Decoder::ReturnFrame(std::shared_ptr<VideoFrame> video_frame) {
  returned_frames_.push_back(video_frame);
  TryReturnFrames();
}

void H264Decoder::TryReturnFrames() {
  while (!returned_frames_.empty()) {
    std::shared_ptr<VideoFrame> frame = returned_frames_.back();
    if (frame->index >= video_frames_.size() || frame != video_frames_[frame->index].frame) {
      // Possible if the stream size changed.
      returned_frames_.pop_back();
      continue;
    }
    if (AvScratch7::Get().ReadFrom(owner_->dosbus()).reg_value() == 0) {
      AvScratch7::Get().FromValue(frame->index + 1).WriteTo(owner_->dosbus());
    } else if (AvScratch8::Get().ReadFrom(owner_->dosbus()).reg_value() == 0) {
      AvScratch8::Get().FromValue(frame->index + 1).WriteTo(owner_->dosbus());
    } else {
      // Neither return slot is free, so give up for now. An interrupt
      // signaling completion of a frame should cause this to be tried again.
      // TODO: Try returning frames again after a delay, to ensure this won't
      // hang forever.
      return;
    }
    returned_frames_.pop_back();
  }
}

zx_status_t H264Decoder::InitializeStream() {
  LOG(TRACE, "H264Decoder::InitializeStream()");
  ZX_DEBUG_ASSERT(state_ == DecoderState::kRunning);
  state_ = DecoderState::kWaitingForNewFrames;
  BarrierBeforeRelease();  // For reference_mv_buffer_
  // Ensure empty; may or may not be set at this point.
  reference_mv_buffer_.reset();
  // StreamInfo AKA AvScratch1.
  auto stream_info = StreamInfo::Get().ReadFrom(owner_->dosbus());
  // SequenceInfo AKA AvScratch2.
  auto sequence_info = SequenceInfo::Get().ReadFrom(owner_->dosbus());
  // SampleAspectRatioInfo AKA AvScratch3
  auto sar_info = SampleAspectRatioInfo::Get().ReadFrom(owner_->dosbus());
  uint32_t level_idc = AvScratchA::Get().ReadFrom(owner_->dosbus()).reg_value();
  uint32_t mb_mv_byte = stream_info.mv_size_flag() ? 24 : 96;
  uint32_t mb_width = stream_info.width_in_mbs();
  if (!mb_width && stream_info.total_mbs())
    mb_width = 256;
  if (!mb_width) {
    DECODE_ERROR("Width is 0 macroblocks");
    // Not returning ZX_ERR_IO_DATA_INTEGRITY, because this isn't an explicit
    // integrity check.
    return ZX_ERR_INTERNAL;
  }
  uint32_t mb_height = stream_info.total_mbs() / mb_width;

  constexpr uint32_t kMaxDimension = 4096;
  constexpr uint32_t kMacroblockPixels = 16;

  if (mb_width > kMaxDimension / kMacroblockPixels ||
      mb_height > kMaxDimension / kMacroblockPixels) {
    DECODE_ERROR("Unsupported dimensions %dx%d macroblocks", mb_width, mb_height);
    return ZX_ERR_INTERNAL;
  }

  uint32_t max_dpb_size = GetMaxDpbSize(level_idc, mb_width, mb_height);
  if (max_dpb_size == 0) {
    LOG(WARN,
        "level_idc, mb_width and/or mb_height invalid? - level_idc: %u mb_width: %u mb_height: %u",
        level_idc, mb_width, mb_height);
    return ZX_ERR_INTERNAL;
  }
  // GetMaxDpbSize() returns max 16, but kMaxActualDPBSize is 24.
  ZX_DEBUG_ASSERT(max_dpb_size < kMaxActualDPBSize);

  // |max_reference_size| comes directly from max_num_ref_frames from the bitstream. Fix it up at
  // least enough to avoid crashes, but if this value is invalid it's possible anything else in the
  // bitstream could be broken.
  uint32_t max_reference_size = stream_info.max_reference_size();
  if (max_reference_size > max_dpb_size) {
    LOG(WARN,
        "max_reference_size is too large - clamping - max_reference_size: %u max_dpb_size: %u",
        max_reference_size, max_dpb_size);
    max_reference_size = max_dpb_size;
  } else if (max_reference_size == 0) {
    // This is technically permissible by the h.264 spec, but still try to increase it to avoid
    // issues.
    LOG(WARN, "max_reference_size is zero - unexpected - using default: %u", max_dpb_size);
    max_reference_size = max_dpb_size;
  }

  // The HW decoder / firmware seems to require several extra frames or it won't continue decoding
  // frames. TODO(fxb/43085): Verify whether min_buffer_count_for_camping (as opposed to
  // min_buffer_count) can be reduced to max_dpb_size + 1, which is what you would expect based on
  // max_num_reorder_frames from the h.264 spec.
  constexpr uint32_t kDbpSizeAdj = 6;
  // Seems needed for decoding bear.h264, but unclear why.
  constexpr uint32_t kAbsoluteMinBufferCount = 10u;
  // Technically the max we should need to camp on to decode is max_dpb_size + 1. That's because a
  // frame is guaranteed to be output when the DPB is full and the hardware tries to insert the
  // newly-decoding frame into it. That's also the minimum because until the DPB is full we don't
  // know which frame should be output first (except in certain special cases like IDR frames or SEI
  // data reducing the limit).
  // In practice the firmware won't necessarily output frames immediately, so we need to add on some
  // slack. |max_reference_size| + 6 is what the linux driver does in low memory situations, so it
  // should normally work. However, when max_dpb_size and max_reference_size are very low (like in
  // bear.h264) that isn't always enough for the firmware, so we require at least 10.
  uint32_t min_buffer_count = std::max(std::max(max_reference_size + kDbpSizeAdj, max_dpb_size + 1),
                                       kAbsoluteMinBufferCount);
  ZX_DEBUG_ASSERT(min_buffer_count < kMaxActualDPBSize);

  // These we pass back to the firmware later, having computed/adjusted as above.
  next_max_dpb_size_ = max_dpb_size;
  // We need to store reference MVs for all active reference frames, as well as 1 extra for the
  // frame that's being decoded into (in case it later becomes a reference frame).
  next_mv_buffer_count_ = max_reference_size + 1;

  // Rounding to 4 macroblocks is for matching the linux driver, in case the
  // hardware happens to round up as well.
  uint32_t mv_buffer_size = fbl::round_up(mb_height, 4u) * fbl::round_up(mb_width, 4u) *
                            mb_mv_byte * next_mv_buffer_count_;
  uint32_t mv_buffer_alloc_size = fbl::round_up(mv_buffer_size, ZX_PAGE_SIZE);

  auto create_result = InternalBuffer::Create("H264ReferenceMvs", &owner_->SysmemAllocatorSyncPtr(),
                                              owner_->bti(), mv_buffer_alloc_size, is_secure_,
                                              /*is_writable=*/true, /*is_mapping_needed*/ false);
  if (!create_result.is_ok()) {
    LOG(ERROR, "Couldn't allocate reference mv buffer - status: %d", create_result.error());
    return create_result.error();
  }
  reference_mv_buffer_.emplace(create_result.take_value());

  // sysmem ensure that newly allocated buffers are zeroed and flushed to RAM and fenced, to the
  // degree possible.

  BarrierAfterFlush();
  AvScratch1::Get()
      .FromValue(truncate_to_32(reference_mv_buffer_->phys_base()))
      .WriteTo(owner_->dosbus());
  // In the linux driver AvScratch3 is used to communicate about the display
  // canvas.
  AvScratch3::Get().FromValue(0).WriteTo(owner_->dosbus());
  AvScratch4::Get()
      .FromValue(truncate_to_32(reference_mv_buffer_->phys_base() + mv_buffer_size))
      .WriteTo(owner_->dosbus());

  auto crop_info = CropInfo::Get().ReadFrom(owner_->dosbus());
  uint32_t display_width = mb_width * 16 - crop_info.right();
  uint32_t display_height = mb_height * 16 - crop_info.bottom();

  // Canvas width must be a multiple of 32 bytes.
  uint32_t coded_width = fbl::round_up(mb_width * 16, 32u);
  uint32_t coded_height = mb_height * 16;

  // Sample aspect ratio - normalize as sar_width : sar_height.
  //
  // The has_sar will be true for any explicitly-specified SAR, and false for
  // all other cases (both explicitly "Unspecified" and "Reserved" cases that we
  // don't recognize).
  bool has_sar = false;
  uint32_t sar_width = 1;
  uint32_t sar_height = 1;
  if (sequence_info.aspect_ratio_info_present_flag()) {
    uint32_t aspect_ratio_idc = sequence_info.aspect_ratio_idc();
    if (aspect_ratio_idc == kAspectRatioIdcExtendedSar) {
      sar_width = sar_info.sar_width();
      sar_height = sar_info.sar_height();
      has_sar = true;
      if (sar_width == 0 || sar_height == 0) {
        // spec says this condition means "considered unspecified"
        sar_width = 1;
        sar_height = 1;
        has_sar = false;
      }
    } else {
      ZX_DEBUG_ASSERT(aspect_ratio_idc != kAspectRatioIdcExtendedSar);
      // aspect_ratio_idc == 0 and "Reserved" values are treated the same way as
      // each other, and both cases don't run the body of the following "if". We
      // treat "Reserved" the same as "Unspecified" instead of flagging an error
      // because it seems extremely unlikely that any "Reserved" value in this
      // context would have meaning beyond specifying sar_width and sar_height.
      // So for "Reserved" values we just end up with has_sar false, which
      // should allow _something_ to be displayed even if the displayed frames
      // have the wrong SAR.
      if (aspect_ratio_idc >= 1 && aspect_ratio_idc <= 16) {
        sar_width = kSarTable[aspect_ratio_idc].sar_width;
        sar_height = kSarTable[aspect_ratio_idc].sar_height;
        has_sar = true;
      }
      ZX_DEBUG_ASSERT(aspect_ratio_idc != 0 || (!has_sar && sar_width == 1 && sar_height == 1));
      ZX_DEBUG_ASSERT(has_sar || (sar_width == 1 && sar_height == 1));
      ZX_DEBUG_ASSERT(sar_width != 0 && sar_height != 0);
    }
  }

  // The actual # of buffers is determined by sysmem, but constrainted by "max_dpb_size" as the min
  // # of needed buffers for reference and re-ordering purposes, not counting decode-into buffer.
  // The "max" means the max the stream might require, so that's actually the min # of buffers we
  // need.  The +1 accounts for the decode-into buffer (AFAICT).  Reduce this number at your own
  // risk - YMMV.
  LOG(TRACE, "max_reference_size: %u max_dpb_size: %u min_buffer_count: %u", max_reference_size,
      max_dpb_size, min_buffer_count);
  uint32_t min_frame_count = min_buffer_count;
  // Also constrained by the maximum number of buffers this driver knows how to track for now, which
  // is kMaxActualDPBSize (24).
  uint32_t max_frame_count = kMaxActualDPBSize;
  zx_status_t status =
      InitializeFrames(min_frame_count, max_frame_count, coded_width, coded_height, display_width,
                       display_height, has_sar, sar_width, sar_height);
  if (status != ZX_OK) {
    if (status != ZX_ERR_STOP) {
      DECODE_ERROR("InitializeFrames() failed: status: %d", status);
    }
    return status;
  }

  return ZX_OK;
}

void H264Decoder::ReceivedFrames(uint32_t frame_count) {
  uint32_t error_count = AvScratchD::Get().ReadFrom(owner_->dosbus()).reg_value();
  // This hit_eos is _not_ the same as the is_end_of_stream in PtsOut below.
  bool hit_eos = false;
  for (uint32_t i = 0; i < frame_count && !hit_eos; i++) {
    auto pic_info = PicInfo::Get(i).ReadFrom(owner_->dosbus());
    uint32_t buffer_index = pic_info.buffer_index();
    uint32_t slice_type =
        (AvScratchH::Get().ReadFrom(owner_->dosbus()).reg_value() >> (i * 4)) & 0xf;
    if (pic_info.eos())
      hit_eos = true;

    uint32_t stream_byte_offset = pic_info.stream_offset();
    stream_byte_offset |=
        ((AvScratch::Get(0xa + i / 2).ReadFrom(owner_->dosbus()).reg_value() >> ((i % 2) * 16)) &
         0xffff)
        << 16;
    // At this point, it may seem like stream_byte_offset is 32 bits, but it's actually only 28
    // bits (checked on astro).  In any case we need 64 bit offset, and pts_manager_ knows how to
    // bit-extend.
    PtsManager::LookupResult pts_result = pts_manager_->Lookup(stream_byte_offset);
    video_frames_[buffer_index].frame->has_pts = pts_result.has_pts();
    video_frames_[buffer_index].frame->pts = pts_result.pts();
    if (pts_result.is_end_of_stream()) {
      // TODO(dustingreen): Handle this once we're able to detect this way.  For
      // now, ignore but print an obvious message.
      printf("##### UNHANDLED END OF STREAM DETECTED #####\n");
      break;
    }

    client_->OnFrameReady(video_frames_[buffer_index].frame);
    DLOG("Got buffer %d error %d error_count %d slice_type %d offset %x", buffer_index,
         pic_info.error(), error_count, slice_type, pic_info.stream_offset());
  }
  AvScratch0::Get().FromValue(0).WriteTo(owner_->dosbus());
}

enum {
  kCommandNone = 0,
  kCommandInitializeStream = 1,
  kCommandNewFrames = 2,
  kCommandSwitchStreams = 3,
  kCommandFatalError = 6,
  kCommandGotFirstOffset = 9,
};

void H264Decoder::SwitchStreams() {
  // Signal that we're ready to allocate new frames for the new stream.
  AvScratch7::Get().FromValue(0).WriteTo(owner_->dosbus());
  AvScratch8::Get().FromValue(0).WriteTo(owner_->dosbus());
  AvScratch9::Get().FromValue(0).WriteTo(owner_->dosbus());

  // Signal firmware that command has been processed.
  AvScratch0::Get().FromValue(0).WriteTo(owner_->dosbus());
}

void H264Decoder::HandleInterrupt() {
  TRACE_DURATION("media", "H264Decoder::HandleInterrupt");
  // Stop processing on fatal error.
  if (fatal_error_)
    return;

  VdecAssistMbox1ClrReg::Get().FromValue(1).WriteTo(owner_->dosbus());

  // Some returned frames may have been buffered up earlier, so try to return
  // them now that the firmware had a chance to do some work.
  TryReturnFrames();

  // The core signals the main processor what command to run using AvScratch0.
  // The main processor returns a result using AvScratch0 to trigger the decoder
  // to continue (possibly 0, if no result is needed).
  auto scratch0 = AvScratch0::Get().ReadFrom(owner_->dosbus());
  DLOG("Got command: %x", scratch0.reg_value());
  uint32_t cpu_command = scratch0.reg_value() & 0xff;
  TRACE_INSTANT("media", "got cpu command", TRACE_SCOPE_THREAD, "cpu_command", cpu_command);
  switch (cpu_command) {
    case kCommandNone:
      // It is possible that the interrupt will fire with no command. This could happen if there is
      // an SEI message that should be acknowledged. This should not be treated as an error.
      break;

    case kCommandInitializeStream: {
      zx_status_t status = InitializeStream();
      if (status != ZX_OK) {
        if (status == ZX_ERR_STOP) {
          LOG(TRACE, "InitializeStream() detected EOS on output");
          break;
        }
        ZX_DEBUG_ASSERT(status != ZX_ERR_STOP);
        LOG(ERROR, "InitializeStream() failed - status: %d", status);
        OnFatalError();
      }
    } break;

    case kCommandNewFrames:
      ReceivedFrames((scratch0.reg_value() >> 8) & 0xff);
      break;

    case kCommandSwitchStreams:
      SwitchStreams();
      break;

    case kCommandFatalError: {
      auto error_count = AvScratchD::Get().ReadFrom(owner_->dosbus()).reg_value();
      DECODE_ERROR("Decoder fatal error %d", error_count);
      owner_->core()->StopDecoding();
      // We need to reset the hardware here or for some malformed hardware streams (e.g.
      // bear_h264[638] = 44) the CPU will hang when trying to isolate VDEC1 power on shutdown.
      ResetHardware();
      LOG(ERROR, "kCommandFatalError");
      OnFatalError();
      // Don't write to AvScratch0, so the decoder won't continue.
      break;
    }

    case kCommandGotFirstOffset: {
      uint32_t first_offset = AvScratch1::Get().ReadFrom(owner_->dosbus()).reg_value();
      DLOG("First offset: %d", first_offset);
      AvScratch0::Get().FromValue(0).WriteTo(owner_->dosbus());
      break;
    }

    default:
      DECODE_ERROR("Got unknown command: %d", cpu_command);
  }

  auto sei_itu35_flags = AvScratchJ::Get().ReadFrom(owner_->dosbus()).reg_value();
  if (sei_itu35_flags & (1 << 15)) {
    DLOG("Got Supplemental Enhancement Information buffer");
    AvScratchJ::Get().FromValue(0).WriteTo(owner_->dosbus());
  }
}

void H264Decoder::OnFatalError() {
  if (!fatal_error_) {
    fatal_error_ = true;
    client_->OnError();
  }
}