OvmfPkg/Library/PlatformDebugLibIoPort/DebugLibDetect.c

   1 /** @file
   2   Detection code for hypervisor debug port.
   3   Non-SEC instance, caches the result of detection.
   4
   5   Copyright (c) 2017, Red Hat, Inc.<BR>
   6   SPDX-License-Identifier: BSD-2-Clause-Patent
   7
   8 **/
   9
  10 #include <Base.h>
  11 #include "DebugLibDetect.h"
  12
  13 //
  14 // Set to TRUE if the debug I/O port has been checked
  15 //
  16 STATIC BOOLEAN  mDebugIoPortChecked = FALSE;
  17
  18 //
  19 // Set to TRUE if the debug I/O port is enabled
  20 //
  21 STATIC BOOLEAN  mDebugIoPortFound = FALSE;
  22
  23 /**
  24   This constructor function must not do anything.
  25
  26   Some modules consuming this library instance, such as the DXE Core, invoke
  27   the DEBUG() macro before they explicitly call
  28   ProcessLibraryConstructorList(). Therefore the auto-generated call from
  29   ProcessLibraryConstructorList() to this constructor function may be preceded
  30   by some calls to PlatformDebugLibIoPortFound() below. Hence
  31   PlatformDebugLibIoPortFound() must not rely on anything this constructor
  32   could set up.
  33
  34   @retval RETURN_SUCCESS   The constructor always returns RETURN_SUCCESS.
  35
  36 **/
  37 RETURN_STATUS
  38 EFIAPI
  39 PlatformDebugLibIoPortConstructor (
  40   VOID
  41   )
  42 {
  43   return RETURN_SUCCESS;
  44 }
  45
  46 /**
  47   At the first call, check if the debug I/O port device is present, and cache
  48   the result for later use. At subsequent calls, return the cached result.
  49
  50   @retval TRUE   if the debug I/O port device was detected.
  51   @retval FALSE  otherwise
  52
  53 **/
  54 BOOLEAN
  55 EFIAPI
  56 PlatformDebugLibIoPortFound (
  57   VOID
  58   )
  59 {
  60   if (!mDebugIoPortChecked) {
  61     mDebugIoPortFound   = PlatformDebugLibIoPortDetect ();
  62     mDebugIoPortChecked = TRUE;
  63   }
  64
  65   return mDebugIoPortFound;
  66 }