audk/OvmfPkg/VirtioGpuDxe/DriverBinding.c

/** @file

  Implement the Driver Binding Protocol and the Component Name 2 Protocol for
  the Virtio GPU hybrid driver.

  Copyright (C) 2016, Red Hat, Inc.

  This program and the accompanying materials are licensed and made available
  under the terms and conditions of the BSD License which accompanies this
  distribution. The full text of the license may be found at
  http://opensource.org/licenses/bsd-license.php

  THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS, WITHOUT
  WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.

**/

#include <Library/BaseMemoryLib.h>
#include <Library/DevicePathLib.h>
#include <Library/MemoryAllocationLib.h>
#include <Library/PrintLib.h>
#include <Library/UefiBootServicesTableLib.h>
#include <Library/UefiLib.h>
#include <Protocol/ComponentName2.h>
#include <Protocol/DevicePath.h>
#include <Protocol/DriverBinding.h>
#include <Protocol/PciIo.h>

#include "VirtioGpu.h"

//
// The device path node that describes the Video Output Device Attributes for
// the single head (UEFI child handle) that we support.
//
// The ACPI_DISPLAY_ADR() macro corresponds to Table B-2, section "B.4.2 _DOD"
// in the ACPI 3.0b spec, or more recently, to Table B-379, section "B.3.2
// _DOD" in the ACPI 6.0 spec.
//
STATIC CONST ACPI_ADR_DEVICE_PATH mAcpiAdr = {
  {                                         // Header
    ACPI_DEVICE_PATH,                       //   Type
    ACPI_ADR_DP,                            //   SubType
    { sizeof mAcpiAdr, 0 },                 //   Length
  },
  ACPI_DISPLAY_ADR (                        // ADR
    1,                                      //   DeviceIdScheme: use the ACPI
                                            //     bit-field definitions
    0,                                      //   HeadId
    0,                                      //   NonVgaOutput
    1,                                      //   BiosCanDetect
    0,                                      //   VendorInfo
    ACPI_ADR_DISPLAY_TYPE_EXTERNAL_DIGITAL, //   Type
    0,                                      //   Port
    0                                       //   Index
    )
};

//
// Component Name 2 Protocol implementation.
//
STATIC CONST EFI_UNICODE_STRING_TABLE mDriverNameTable[] = {
  { "en", L"Virtio GPU Driver" },
  { NULL, NULL                 }
};

STATIC
EFI_STATUS
EFIAPI
VirtioGpuGetDriverName (
  IN  EFI_COMPONENT_NAME2_PROTOCOL *This,
  IN  CHAR8                        *Language,
  OUT CHAR16                       **DriverName
  )
{
  return LookupUnicodeString2 (Language, This->SupportedLanguages,
           mDriverNameTable, DriverName, FALSE /* Iso639Language */);
}

STATIC
EFI_STATUS
EFIAPI
VirtioGpuGetControllerName (
  IN  EFI_COMPONENT_NAME2_PROTOCOL *This,
  IN  EFI_HANDLE                   ControllerHandle,
  IN  EFI_HANDLE                   ChildHandle       OPTIONAL,
  IN  CHAR8                        *Language,
  OUT CHAR16                       **ControllerName
  )
{
  EFI_STATUS Status;
  VGPU_DEV   *VgpuDev;

  //
  // Look up the VGPU_DEV "protocol interface" on ControllerHandle.
  //
  Status = gBS->OpenProtocol (ControllerHandle, &gEfiCallerIdGuid,
                  (VOID **)&VgpuDev, gImageHandle, ControllerHandle,
                  EFI_OPEN_PROTOCOL_GET_PROTOCOL);
  if (EFI_ERROR (Status)) {
    return Status;
  }
  //
  // Sanity check: if we found gEfiCallerIdGuid on ControllerHandle, then we
  // keep its Virtio Device Protocol interface open BY_DRIVER.
  //
  ASSERT_EFI_ERROR (EfiTestManagedDevice (ControllerHandle, gImageHandle,
                      &gVirtioDeviceProtocolGuid));

  if (ChildHandle == NULL) {
    //
    // The caller is querying the name of the VGPU_DEV controller.
    //
    return LookupUnicodeString2 (Language, This->SupportedLanguages,
             VgpuDev->BusName, ControllerName, FALSE /* Iso639Language */);
  }

  //
  // Otherwise, the caller is looking for the name of the GOP child controller.
  // Check if it is asking about the GOP child controller that we manage. (The
  // condition below covers the case when we haven't produced the GOP child
  // controller yet, or we've destroyed it since.)
  //
  if (VgpuDev->Child == NULL || ChildHandle != VgpuDev->Child->GopHandle) {
    return EFI_UNSUPPORTED;
  }
  //
  // Sanity check: our GOP child controller keeps the VGPU_DEV controller's
  // Virtio Device Protocol interface open BY_CHILD_CONTROLLER.
  //
  ASSERT_EFI_ERROR (EfiTestChildHandle (ControllerHandle, ChildHandle,
                      &gVirtioDeviceProtocolGuid));

  return LookupUnicodeString2 (Language, This->SupportedLanguages,
           VgpuDev->Child->GopName, ControllerName,
           FALSE /* Iso639Language */);
}

STATIC CONST EFI_COMPONENT_NAME2_PROTOCOL mComponentName2 = {
  VirtioGpuGetDriverName,
  VirtioGpuGetControllerName,
  "en"                       // SupportedLanguages (RFC 4646)
};

//
// Helper functions for the Driver Binding Protocol Implementation.
//
/**
  Format the VGPU_DEV controller name, to be looked up and returned by
  VirtioGpuGetControllerName().

  @param[in] ControllerHandle  The handle that identifies the VGPU_DEV
                               controller.

  @param[in] AgentHandle       The handle of the agent that will attempt to
                               temporarily open the PciIo protocol. This is the
                               DriverBindingHandle member of the
                               EFI_DRIVER_BINDING_PROTOCOL whose Start()
                               function is calling this function.

  @param[in] DevicePath        The device path that is installed on
                               ControllerHandle.

  @param[out] ControllerName   A dynamically allocated unicode string that
                               unconditionally says "Virtio GPU Device", with a
                               PCI Segment:Bus:Device.Function location
                               optionally appended. The latter part is only
                               produced if DevicePath contains at least one
                               PciIo node; in that case, the most specific such
                               node is used for retrieving the location info.
                               The caller is responsible for freeing
                               ControllerName after use.

  @retval EFI_SUCCESS           ControllerName has been formatted.

  @retval EFI_OUT_OF_RESOURCES  Failed to allocate memory for ControllerName.
**/
STATIC
EFI_STATUS
FormatVgpuDevName (
  IN  EFI_HANDLE               ControllerHandle,
  IN  EFI_HANDLE               AgentHandle,
  IN  EFI_DEVICE_PATH_PROTOCOL *DevicePath,
  OUT CHAR16                   **ControllerName
  )
{
  EFI_HANDLE          PciIoHandle;
  EFI_PCI_IO_PROTOCOL *PciIo;
  UINTN               Segment, Bus, Device, Function;
  STATIC CONST CHAR16 ControllerNameStem[] = L"Virtio GPU Device";
  UINTN               ControllerNameSize;

  if (EFI_ERROR (gBS->LocateDevicePath (&gEfiPciIoProtocolGuid, &DevicePath,
                        &PciIoHandle)) ||
      EFI_ERROR (gBS->OpenProtocol (PciIoHandle, &gEfiPciIoProtocolGuid,
                        (VOID **)&PciIo, AgentHandle, ControllerHandle,
                        EFI_OPEN_PROTOCOL_GET_PROTOCOL)) ||
      EFI_ERROR (PciIo->GetLocation (PciIo, &Segment, &Bus, &Device,
                          &Function))) {
    //
    // Failed to retrieve location info, return verbatim copy of static string.
    //
    *ControllerName = AllocateCopyPool (sizeof ControllerNameStem,
                        ControllerNameStem);
    return (*ControllerName == NULL) ? EFI_OUT_OF_RESOURCES : EFI_SUCCESS;
  }
  //
  // Location info available, format ControllerName dynamically.
  //
  ControllerNameSize = sizeof ControllerNameStem + // includes L'\0'
                       sizeof (CHAR16) * (1 + 4 +  // Segment
                                          1 + 2 +  // Bus
                                          1 + 2 +  // Device
                                          1 + 1    // Function
                                          );
  *ControllerName = AllocatePool (ControllerNameSize);
  if (*ControllerName == NULL) {
    return EFI_OUT_OF_RESOURCES;
  }

  UnicodeSPrintAsciiFormat (*ControllerName, ControllerNameSize,
    "%s %04x:%02x:%02x.%x", ControllerNameStem, (UINT32)Segment, (UINT32)Bus,
    (UINT32)Device, (UINT32)Function);
  return EFI_SUCCESS;
}

/**
  Dynamically allocate and initialize the VGPU_GOP child object within an
  otherwise configured parent VGPU_DEV object.

  This function adds a BY_CHILD_CONTROLLER reference to ParentBusController's
  VIRTIO_DEVICE_PROTOCOL interface.

  @param[in,out] ParentBus        The pre-initialized VGPU_DEV object that the
                                  newly created VGPU_GOP object will be the
                                  child of.

  @param[in] ParentDevicePath     The device path protocol instance that is
                                  installed on ParentBusController.

  @param[in] ParentBusController  The UEFI controller handle on which the
                                  ParentBus VGPU_DEV object and the
                                  ParentDevicePath device path protocol are
                                  installed.

  @param[in] DriverBindingHandle  The DriverBindingHandle member of
                                  EFI_DRIVER_BINDING_PROTOCOL whose Start()
                                  function is calling this function. It is
                                  passed as AgentHandle to gBS->OpenProtocol()
                                  when creating the BY_CHILD_CONTROLLER
                                  reference.

  @retval EFI_SUCCESS           ParentBus->Child has been created and
                                populated, and ParentBus->Child->GopHandle now
                                references ParentBusController->VirtIo
                                BY_CHILD_CONTROLLER.

  @retval EFI_OUT_OF_RESOURCES  Memory allocation failed.

  @return                       Error codes from underlying functions.
**/
STATIC
EFI_STATUS
InitVgpuGop (
  IN OUT VGPU_DEV                 *ParentBus,
  IN     EFI_DEVICE_PATH_PROTOCOL *ParentDevicePath,
  IN     EFI_HANDLE               ParentBusController,
  IN     EFI_HANDLE               DriverBindingHandle
  )
{
  VGPU_GOP            *VgpuGop;
  EFI_STATUS          Status;
  CHAR16              *ParentBusName;
  STATIC CONST CHAR16 NameSuffix[] = L" Head #0";
  UINTN               NameSize;
  CHAR16              *Name;
  EFI_TPL             OldTpl;
  VOID                *ParentVirtIo;

  VgpuGop = AllocateZeroPool (sizeof *VgpuGop);
  if (VgpuGop == NULL) {
    return EFI_OUT_OF_RESOURCES;
  }

  VgpuGop->Signature = VGPU_GOP_SIG;
  VgpuGop->ParentBus = ParentBus;

  //
  // Format a human-readable controller name for VGPU_GOP, and stash it for
  // VirtioGpuGetControllerName() to look up. We simply append NameSuffix to
  // ParentBus->BusName.
  //
  Status = LookupUnicodeString2 ("en", mComponentName2.SupportedLanguages,
             ParentBus->BusName, &ParentBusName, FALSE /* Iso639Language */);
  ASSERT_EFI_ERROR (Status);
  NameSize = StrSize (ParentBusName) - sizeof (CHAR16) + sizeof NameSuffix;
  Name = AllocatePool (NameSize);
  if (Name == NULL) {
    Status = EFI_OUT_OF_RESOURCES;
    goto FreeVgpuGop;
  }
  UnicodeSPrintAsciiFormat (Name, NameSize, "%s%s", ParentBusName, NameSuffix);
  Status = AddUnicodeString2 ("en", mComponentName2.SupportedLanguages,
             &VgpuGop->GopName, Name, FALSE /* Iso639Language */);
  FreePool (Name);
  if (EFI_ERROR (Status)) {
    goto FreeVgpuGop;
  }

  //
  // Create the child device path.
  //
  VgpuGop->GopDevicePath = AppendDevicePathNode (ParentDevicePath,
                             &mAcpiAdr.Header);
  if (VgpuGop->GopDevicePath == NULL) {
    Status = EFI_OUT_OF_RESOURCES;
    goto FreeVgpuGopName;
  }

  //
  // Mask protocol notify callbacks until we're done.
  //
  OldTpl = gBS->RaiseTPL (TPL_CALLBACK);

  //
  // Create the child handle with the child device path.
  //
  Status = gBS->InstallProtocolInterface (&VgpuGop->GopHandle,
                  &gEfiDevicePathProtocolGuid, EFI_NATIVE_INTERFACE,
                  VgpuGop->GopDevicePath);
  if (EFI_ERROR (Status)) {
    goto FreeDevicePath;
  }

  //
  // The child handle must present a reference to the parent handle's Virtio
  // Device Protocol interface.
  //
  Status = gBS->OpenProtocol (ParentBusController, &gVirtioDeviceProtocolGuid,
                  &ParentVirtIo, DriverBindingHandle, VgpuGop->GopHandle,
                  EFI_OPEN_PROTOCOL_BY_CHILD_CONTROLLER);
  if (EFI_ERROR (Status)) {
    goto UninstallDevicePath;
  }
  ASSERT (ParentVirtIo == ParentBus->VirtIo);

  //
  // Initialize our Graphics Output Protocol.
  //
  // Fill in the function members of VgpuGop->Gop from the template, then set
  // up the rest of the GOP infrastructure by calling SetMode() right now.
  //
  CopyMem (&VgpuGop->Gop, &mGopTemplate, sizeof mGopTemplate);
  Status = VgpuGop->Gop.SetMode (&VgpuGop->Gop, 0);
  if (EFI_ERROR (Status)) {
    goto CloseVirtIoByChild;
  }

  //
  // Install the Graphics Output Protocol on the child handle.
  //
  Status = gBS->InstallProtocolInterface (&VgpuGop->GopHandle,
                  &gEfiGraphicsOutputProtocolGuid, EFI_NATIVE_INTERFACE,
                  &VgpuGop->Gop);
  if (EFI_ERROR (Status)) {
    goto UninitGop;
  }

  //
  // We're done.
  //
  gBS->RestoreTPL (OldTpl);
  ParentBus->Child = VgpuGop;
  return EFI_SUCCESS;

UninitGop:
  ReleaseGopResources (VgpuGop, TRUE /* DisableHead */);

CloseVirtIoByChild:
  gBS->CloseProtocol (ParentBusController, &gVirtioDeviceProtocolGuid,
    DriverBindingHandle, VgpuGop->GopHandle);

UninstallDevicePath:
  gBS->UninstallProtocolInterface (VgpuGop->GopHandle,
         &gEfiDevicePathProtocolGuid, VgpuGop->GopDevicePath);

FreeDevicePath:
  gBS->RestoreTPL (OldTpl);
  FreePool (VgpuGop->GopDevicePath);

FreeVgpuGopName:
  FreeUnicodeStringTable (VgpuGop->GopName);

FreeVgpuGop:
  FreePool (VgpuGop);

  return Status;
}

/**
  Tear down and release the VGPU_GOP child object within the VGPU_DEV parent
  object.

  This function removes the BY_CHILD_CONTROLLER reference from
  ParentBusController's VIRTIO_DEVICE_PROTOCOL interface.

  @param[in,out] ParentBus        The VGPU_DEV object that the VGPU_GOP child
                                  object will be removed from.

  @param[in] ParentBusController  The UEFI controller handle on which the
                                  ParentBus VGPU_DEV object is installed.

  @param[in] DriverBindingHandle  The DriverBindingHandle member of
                                  EFI_DRIVER_BINDING_PROTOCOL whose Stop()
                                  function is calling this function. It is
                                  passed as AgentHandle to gBS->CloseProtocol()
                                  when removing the BY_CHILD_CONTROLLER
                                  reference.
**/
STATIC
VOID
UninitVgpuGop (
  IN OUT VGPU_DEV   *ParentBus,
  IN     EFI_HANDLE ParentBusController,
  IN     EFI_HANDLE DriverBindingHandle
  )
{
  VGPU_GOP   *VgpuGop;
  EFI_STATUS Status;

  VgpuGop = ParentBus->Child;
  Status = gBS->UninstallProtocolInterface (VgpuGop->GopHandle,
                  &gEfiGraphicsOutputProtocolGuid, &VgpuGop->Gop);
  ASSERT_EFI_ERROR (Status);

  //
  // Uninitialize VgpuGop->Gop.
  //
  ReleaseGopResources (VgpuGop, TRUE /* DisableHead */);

  Status = gBS->CloseProtocol (ParentBusController, &gVirtioDeviceProtocolGuid,
                  DriverBindingHandle, VgpuGop->GopHandle);
  ASSERT_EFI_ERROR (Status);

  Status = gBS->UninstallProtocolInterface (VgpuGop->GopHandle,
                  &gEfiDevicePathProtocolGuid, VgpuGop->GopDevicePath);
  ASSERT_EFI_ERROR (Status);

  FreePool (VgpuGop->GopDevicePath);
  FreeUnicodeStringTable (VgpuGop->GopName);
  FreePool (VgpuGop);

  ParentBus->Child = NULL;
}

//
// Driver Binding Protocol Implementation.
//
STATIC
EFI_STATUS
EFIAPI
VirtioGpuDriverBindingSupported (
  IN EFI_DRIVER_BINDING_PROTOCOL *This,
  IN EFI_HANDLE                  ControllerHandle,
  IN EFI_DEVICE_PATH_PROTOCOL    *RemainingDevicePath OPTIONAL
  )
{
  EFI_STATUS             Status;
  VIRTIO_DEVICE_PROTOCOL *VirtIo;

  //
  // - If RemainingDevicePath is NULL: the caller is interested in creating all
  //   child handles.
  // - If RemainingDevicePath points to an end node: the caller is not
  //   interested in creating any child handle.
  // - Otherwise, the caller would like to create the one child handle
  //   specified in RemainingDevicePath. In this case we have to see if the
  //   requested device path is supportable.
  //
  if (RemainingDevicePath != NULL &&
      !IsDevicePathEnd (RemainingDevicePath) &&
      (DevicePathNodeLength (RemainingDevicePath) != sizeof mAcpiAdr ||
       CompareMem (RemainingDevicePath, &mAcpiAdr, sizeof mAcpiAdr) != 0)) {
    return EFI_UNSUPPORTED;
  }

  //
  // Open the Virtio Device Protocol interface on the controller, BY_DRIVER.
  //
  Status = gBS->OpenProtocol (ControllerHandle, &gVirtioDeviceProtocolGuid,
                  (VOID **)&VirtIo, This->DriverBindingHandle,
                  ControllerHandle, EFI_OPEN_PROTOCOL_BY_DRIVER);
  if (EFI_ERROR (Status)) {
    //
    // If this fails, then by default we cannot support ControllerHandle. There
    // is one exception: we've already bound the device, have not produced any
    // GOP child controller, and now the caller wants us to produce the child
    // controller (either specifically or as part of "all children"). That's
    // allowed.
    //
    if (Status == EFI_ALREADY_STARTED) {
      EFI_STATUS Status2;
      VGPU_DEV   *VgpuDev;

      Status2 = gBS->OpenProtocol (ControllerHandle, &gEfiCallerIdGuid,
                       (VOID **)&VgpuDev, This->DriverBindingHandle,
                       ControllerHandle, EFI_OPEN_PROTOCOL_GET_PROTOCOL);
      ASSERT_EFI_ERROR (Status2);

      if (VgpuDev->Child == NULL &&
          (RemainingDevicePath == NULL ||
           !IsDevicePathEnd (RemainingDevicePath))) {
        Status = EFI_SUCCESS;
      }
    }

    return Status;
  }

  //
  // First BY_DRIVER open; check the VirtIo revision and subsystem.
  //
  if (VirtIo->Revision < VIRTIO_SPEC_REVISION (1, 0, 0) ||
      VirtIo->SubSystemDeviceId != VIRTIO_SUBSYSTEM_GPU_DEVICE) {
    Status = EFI_UNSUPPORTED;
    goto CloseVirtIo;
  }

  //
  // We'll need the device path of the VirtIo device both for formatting
  // VGPU_DEV.BusName and for populating VGPU_GOP.GopDevicePath.
  //
  Status = gBS->OpenProtocol (ControllerHandle, &gEfiDevicePathProtocolGuid,
                  NULL, This->DriverBindingHandle, ControllerHandle,
                  EFI_OPEN_PROTOCOL_TEST_PROTOCOL);

CloseVirtIo:
  gBS->CloseProtocol (ControllerHandle, &gVirtioDeviceProtocolGuid,
    This->DriverBindingHandle, ControllerHandle);

  return Status;
}

STATIC
EFI_STATUS
EFIAPI
VirtioGpuDriverBindingStart (
  IN EFI_DRIVER_BINDING_PROTOCOL *This,
  IN EFI_HANDLE                  ControllerHandle,
  IN EFI_DEVICE_PATH_PROTOCOL    *RemainingDevicePath OPTIONAL
  )
{
  EFI_STATUS               Status;
  VIRTIO_DEVICE_PROTOCOL   *VirtIo;
  BOOLEAN                  VirtIoBoundJustNow;
  VGPU_DEV                 *VgpuDev;
  EFI_DEVICE_PATH_PROTOCOL *DevicePath;

  //
  // Open the Virtio Device Protocol.
  //
  // The result of this operation, combined with the checks in
  // VirtioGpuDriverBindingSupported(), uniquely tells us whether we are
  // binding the VirtIo controller on this call (with or without creating child
  // controllers), or else we're *only* creating child controllers.
  //
  Status = gBS->OpenProtocol (ControllerHandle, &gVirtioDeviceProtocolGuid,
                  (VOID **)&VirtIo, This->DriverBindingHandle,
                  ControllerHandle, EFI_OPEN_PROTOCOL_BY_DRIVER);
  if (EFI_ERROR (Status)) {
    //
    // The assertions below are based on the success of
    // VirtioGpuDriverBindingSupported(): we bound ControllerHandle earlier,
    // without producing child handles, and now we're producing the GOP child
    // handle only.
    //
    ASSERT (Status == EFI_ALREADY_STARTED);

    Status = gBS->OpenProtocol (ControllerHandle, &gEfiCallerIdGuid,
                    (VOID **)&VgpuDev, This->DriverBindingHandle,
                    ControllerHandle, EFI_OPEN_PROTOCOL_GET_PROTOCOL);
    ASSERT_EFI_ERROR (Status);

    ASSERT (VgpuDev->Child == NULL);
    ASSERT (
      RemainingDevicePath == NULL || !IsDevicePathEnd (RemainingDevicePath));

    VirtIoBoundJustNow = FALSE;
  } else {
    VirtIoBoundJustNow = TRUE;

    //
    // Allocate the private structure.
    //
    VgpuDev = AllocateZeroPool (sizeof *VgpuDev);
    if (VgpuDev == NULL) {
      Status = EFI_OUT_OF_RESOURCES;
      goto CloseVirtIo;
    }
    VgpuDev->VirtIo = VirtIo;
  }

  //
  // Grab the VirtIo controller's device path. This is necessary regardless of
  // VirtIoBoundJustNow.
  //
  Status = gBS->OpenProtocol (ControllerHandle, &gEfiDevicePathProtocolGuid,
                  (VOID **)&DevicePath, This->DriverBindingHandle,
                  ControllerHandle, EFI_OPEN_PROTOCOL_GET_PROTOCOL);
  if (EFI_ERROR (Status)) {
    goto FreeVgpuDev;
  }

  //
  // Create VGPU_DEV if we've bound the VirtIo controller right now (that is,
  // if we aren't *only* creating child handles).
  //
  if (VirtIoBoundJustNow) {
    CHAR16 *VgpuDevName;

    //
    // Format a human-readable controller name for VGPU_DEV, and stash it for
    // VirtioGpuGetControllerName() to look up.
    //
    Status = FormatVgpuDevName (ControllerHandle, This->DriverBindingHandle,
               DevicePath, &VgpuDevName);
    if (EFI_ERROR (Status)) {
      goto FreeVgpuDev;
    }
    Status = AddUnicodeString2 ("en", mComponentName2.SupportedLanguages,
               &VgpuDev->BusName, VgpuDevName, FALSE /* Iso639Language */);
    FreePool (VgpuDevName);
    if (EFI_ERROR (Status)) {
      goto FreeVgpuDev;
    }

    Status = VirtioGpuInit (VgpuDev);
    if (EFI_ERROR (Status)) {
      goto FreeVgpuDevBusName;
    }

    Status = gBS->CreateEvent (EVT_SIGNAL_EXIT_BOOT_SERVICES, TPL_CALLBACK,
                    VirtioGpuExitBoot, VgpuDev /* NotifyContext */,
                    &VgpuDev->ExitBoot);
    if (EFI_ERROR (Status)) {
      goto UninitGpu;
    }

    //
    // Install the VGPU_DEV "protocol interface" on ControllerHandle.
    //
    Status = gBS->InstallProtocolInterface (&ControllerHandle,
                    &gEfiCallerIdGuid, EFI_NATIVE_INTERFACE, VgpuDev);
    if (EFI_ERROR (Status)) {
      goto CloseExitBoot;
    }

    if (RemainingDevicePath != NULL && IsDevicePathEnd (RemainingDevicePath)) {
      //
      // No child handle should be produced; we're done.
      //
      DEBUG ((EFI_D_INFO, "%a: bound VirtIo=%p without producing GOP\n",
        __FUNCTION__, (VOID *)VgpuDev->VirtIo));
      return EFI_SUCCESS;
    }
  }

  //
  // Below we'll produce our single child handle: the caller requested it
  // either specifically, or as part of all child handles.
  //
  ASSERT (VgpuDev->Child == NULL);
  ASSERT (
    RemainingDevicePath == NULL || !IsDevicePathEnd (RemainingDevicePath));

  Status = InitVgpuGop (VgpuDev, DevicePath, ControllerHandle,
             This->DriverBindingHandle);
  if (EFI_ERROR (Status)) {
    goto UninstallVgpuDev;
  }

  //
  // We're done.
  //
  DEBUG ((EFI_D_INFO, "%a: produced GOP %a VirtIo=%p\n", __FUNCTION__,
    VirtIoBoundJustNow ? "while binding" : "for pre-bound",
    (VOID *)VgpuDev->VirtIo));
  return EFI_SUCCESS;

UninstallVgpuDev:
  if (VirtIoBoundJustNow) {
    gBS->UninstallProtocolInterface (ControllerHandle, &gEfiCallerIdGuid,
           VgpuDev);
  }

CloseExitBoot:
  if (VirtIoBoundJustNow) {
    gBS->CloseEvent (VgpuDev->ExitBoot);
  }

UninitGpu:
  if (VirtIoBoundJustNow) {
    VirtioGpuUninit (VgpuDev);
  }

FreeVgpuDevBusName:
  if (VirtIoBoundJustNow) {
    FreeUnicodeStringTable (VgpuDev->BusName);
  }

FreeVgpuDev:
  if (VirtIoBoundJustNow) {
    FreePool (VgpuDev);
  }

CloseVirtIo:
  if (VirtIoBoundJustNow) {
    gBS->CloseProtocol (ControllerHandle, &gVirtioDeviceProtocolGuid,
      This->DriverBindingHandle, ControllerHandle);
  }

  return Status;
}

STATIC
EFI_STATUS
EFIAPI
VirtioGpuDriverBindingStop (
  IN  EFI_DRIVER_BINDING_PROTOCOL *This,
  IN  EFI_HANDLE                  ControllerHandle,
  IN  UINTN                       NumberOfChildren,
  IN  EFI_HANDLE                  *ChildHandleBuffer OPTIONAL
  )
{
  EFI_STATUS Status;
  VGPU_DEV   *VgpuDev;

  //
  // Look up the VGPU_DEV "protocol interface" on ControllerHandle.
  //
  Status = gBS->OpenProtocol (ControllerHandle, &gEfiCallerIdGuid,
                  (VOID **)&VgpuDev, This->DriverBindingHandle,
                  ControllerHandle, EFI_OPEN_PROTOCOL_GET_PROTOCOL);
  if (EFI_ERROR (Status)) {
    return Status;
  }
  //
  // Sanity check: if we found gEfiCallerIdGuid on ControllerHandle, then we
  // keep its Virtio Device Protocol interface open BY_DRIVER.
  //
  ASSERT_EFI_ERROR (EfiTestManagedDevice (ControllerHandle,
                      This->DriverBindingHandle, &gVirtioDeviceProtocolGuid));

  switch (NumberOfChildren) {
  case 0:
    //
    // The caller wants us to unbind the VirtIo controller.
    //
    if (VgpuDev->Child != NULL) {
      //
      // We still have the GOP child.
      //
      Status = EFI_DEVICE_ERROR;
      break;
    }

    DEBUG ((EFI_D_INFO, "%a: unbinding GOP-less VirtIo=%p\n", __FUNCTION__,
      (VOID *)VgpuDev->VirtIo));

    Status = gBS->UninstallProtocolInterface (ControllerHandle,
                    &gEfiCallerIdGuid, VgpuDev);
    ASSERT_EFI_ERROR (Status);

    Status = gBS->CloseEvent (VgpuDev->ExitBoot);
    ASSERT_EFI_ERROR (Status);

    VirtioGpuUninit (VgpuDev);
    FreeUnicodeStringTable (VgpuDev->BusName);
    FreePool (VgpuDev);

    Status = gBS->CloseProtocol (ControllerHandle, &gVirtioDeviceProtocolGuid,
                    This->DriverBindingHandle, ControllerHandle);
    ASSERT_EFI_ERROR (Status);
    break;

  case 1:
    //
    // The caller wants us to destroy our child GOP controller.
    //
    if (VgpuDev->Child == NULL ||
        ChildHandleBuffer[0] != VgpuDev->Child->GopHandle) {
      //
      // We have no child controller at the moment, or it differs from the one
      // the caller wants us to destroy. I.e., we don't own the child
      // controller passed in.
      //
      Status = EFI_DEVICE_ERROR;
      break;
    }
    //
    // Sanity check: our GOP child controller keeps the VGPU_DEV controller's
    // Virtio Device Protocol interface open BY_CHILD_CONTROLLER.
    //
    ASSERT_EFI_ERROR (EfiTestChildHandle (ControllerHandle,
                        VgpuDev->Child->GopHandle,
                        &gVirtioDeviceProtocolGuid));

    DEBUG ((EFI_D_INFO, "%a: destroying GOP under VirtIo=%p\n", __FUNCTION__,
      (VOID *)VgpuDev->VirtIo));
    UninitVgpuGop (VgpuDev, ControllerHandle, This->DriverBindingHandle);
    break;

  default:
    //
    // Impossible, we never produced more than one child.
    //
    Status = EFI_DEVICE_ERROR;
    break;
  }
  return Status;
}

STATIC EFI_DRIVER_BINDING_PROTOCOL mDriverBinding = {
  VirtioGpuDriverBindingSupported,
  VirtioGpuDriverBindingStart,
  VirtioGpuDriverBindingStop,
  0x10,                            // Version
  NULL,                            // ImageHandle, overwritten in entry point
  NULL                             // DriverBindingHandle, ditto
};

//
// Entry point of the driver.
//
EFI_STATUS
EFIAPI
VirtioGpuEntryPoint (
  IN EFI_HANDLE       ImageHandle,
  IN EFI_SYSTEM_TABLE *SystemTable
  )
{
  return EfiLibInstallDriverBindingComponentName2 (ImageHandle, SystemTable,
           &mDriverBinding, ImageHandle, NULL /* ComponentName */,
           &mComponentName2);
}