OvmfPkg/Library/PlatformDebugLibIoPort/DebugLibDetect.c

   1 /** @file
   2   Detection code for QEMU debug port.
   3   Non-SEC instance, caches the result of detection.
   4
   5   Copyright (c) 2017, Red Hat, Inc.<BR>
   6   This program and the accompanying materials
   7   are licensed and made available under the terms and conditions of the BSD License
   8   which accompanies this distribution.  The full text of the license may be found at
   9   http://opensource.org/licenses/bsd-license.php.
  10
  11   THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
  12   WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
  13
  14 **/
  15
  16 #include <Base.h>
  17 #include "DebugLibDetect.h"
  18
  19 //
  20 // Set to TRUE if the debug I/O port has been checked
  21 //
  22 STATIC BOOLEAN mDebugIoPortChecked = FALSE;
  23
  24 //
  25 // Set to TRUE if the debug I/O port is enabled
  26 //
  27 STATIC BOOLEAN mDebugIoPortFound = FALSE;
  28
  29 /**
  30   This constructor function must not do anything.
  31
  32   Some modules consuming this library instance, such as the DXE Core, invoke
  33   the DEBUG() macro before they explicitly call
  34   ProcessLibraryConstructorList(). Therefore the auto-generated call from
  35   ProcessLibraryConstructorList() to this constructor function may be preceded
  36   by some calls to PlatformDebugLibIoPortFound() below. Hence
  37   PlatformDebugLibIoPortFound() must not rely on anything this constructor
  38   could set up.
  39
  40   @retval RETURN_SUCCESS   The constructor always returns RETURN_SUCCESS.
  41
  42 **/
  43 RETURN_STATUS
  44 EFIAPI
  45 PlatformDebugLibIoPortConstructor (
  46   VOID
  47   )
  48 {
  49   return RETURN_SUCCESS;
  50 }
  51
  52 /**
  53   At the first call, check if the debug I/O port device is present, and cache
  54   the result for later use. At subsequent calls, return the cached result.
  55
  56   @retval TRUE   if the debug I/O port device was detected.
  57   @retval FALSE  otherwise
  58
  59 **/
  60 BOOLEAN
  61 EFIAPI
  62 PlatformDebugLibIoPortFound (
  63   VOID
  64   )
  65 {
  66   if (!mDebugIoPortChecked) {
  67     mDebugIoPortFound = PlatformDebugLibIoPortDetect ();
  68     mDebugIoPortChecked = TRUE;
  69   }
  70   return mDebugIoPortFound;
  71 }