ArmPkg/Library/ArmGicArchLib/Arm/ArmGicArchLib.c

   1 /** @file
   2 *
   3 *  Copyright (c) 2014, ARM Limited. All rights reserved.
   4 *
   5 *  This program and the accompanying materials are licensed and made available
   6 *  under the terms and conditions of the BSD License which accompanies this
   7 *  distribution.  The full text of the license may be found at
   8 *  http://opensource.org/licenses/bsd-license.php
   9 *
  10 *  THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
  11 *  WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
  12 *
  13 **/
  14
  15 #include <Library/ArmLib.h>
  16 #include <Library/ArmGicLib.h>
  17
  18 ARM_GIC_ARCH_REVISION
  19 EFIAPI
  20 ArmGicGetSupportedArchRevision (
  21   VOID
  22   )
  23 {
  24   UINT32    IccSre;
  25
  26   // Ideally we would like to use the GICC IIDR Architecture version here, but
  27   // this does not seem to be very reliable as the implementation could easily
  28   // get it wrong. It is more reliable to check if the GICv3 System Register
  29   // feature is implemented on the CPU. This is also convenient as our GICv3
  30   // driver requires SRE. If only Memory mapped access is available we try to
  31   // drive the GIC as a v2.
  32   if (ArmReadIdPfr1 () & ARM_PFR1_GIC) {
  33     // Make sure System Register access is enabled (SRE). This depends on the
  34     // higher privilege level giving us permission, otherwise we will either
  35     // cause an exception here, or the write doesn't stick in which case we need
  36     // to fall back to the GICv2 MMIO interface.
  37     // Note: We do not need to set ICC_SRE_EL2.Enable because the OS is started
  38     // at the same exception level.
  39     // It is the OS responsibility to set this bit.
  40     IccSre = ArmGicV3GetControlSystemRegisterEnable ();
  41     if (!(IccSre & ICC_SRE_EL2_SRE)) {
  42       ArmGicV3SetControlSystemRegisterEnable (IccSre| ICC_SRE_EL2_SRE);
  43       IccSre = ArmGicV3GetControlSystemRegisterEnable ();
  44     }
  45     if (IccSre & ICC_SRE_EL2_SRE) {
  46       return ARM_GIC_ARCH_REVISION_3;
  47     }
  48   }
  49
  50   return ARM_GIC_ARCH_REVISION_2;
  51 }