[PATCH] ArmPkg: ARM v8.2 updates for detecting FP

[evan.lloyd@arm.com]

From: Sami Mujawar <samimujawar>

The ARMv8.2-FP16 extension introduces support for half precision
floating point and the processor ID registers have been updated to
enable detection of the implementation.

The possible values for the FP bits in ID_AA64PFR0_EL1[19:16] are:
  - 0000 : Floating-point is implemented.
  - 0001 : Floating-point including Half-precision support is
           implemented.
  - 1111 : Floating-point is not implemented.
  - All other values are reserved.

Previously ArmEnableVFP() compared the FP bits with 0000b to see if
the FP was implemented, before enabling FP. Modified this check to
enable the FP if the FP bits 19:16 are not 1111b.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Sami Mujawar <sami.mujawar@arm.com>
Signed-off-by: Evan Lloyd <evan.lloyd@arm.com>
---
 ArmPkg/Library/ArmLib/AArch64/AArch64Support.S | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/ArmPkg/Library/ArmLib/AArch64/AArch64Support.S b/ArmPkg/Library/ArmLib/AArch64/AArch64Support.S
index dde6a756528f3abf1bd5a142448e42122a9bd8fa..2d136d242b943fe2f365bc824953b7fe10c944b7 100644
--- a/ArmPkg/Library/ArmLib/AArch64/AArch64Support.S
+++ b/ArmPkg/Library/ArmLib/AArch64/AArch64Support.S
@@ -1,7 +1,7 @@
 #------------------------------------------------------------------------------
 #
 # Copyright (c) 2008 - 2010, Apple Inc. All rights reserved.<BR>
-# Copyright (c) 2011 - 2014, ARM Limited. All rights reserved.
+# Copyright (c) 2011 - 2017, ARM Limited. All rights reserved.
 # Copyright (c) 2016, Linaro Limited. All rights reserved.
 #
 # This program and the accompanying materials
@@ -403,9 +403,11 @@ ASM_FUNC(ArmEnableVFP)
   mov   x1, x30                 // Save LR
   bl    ArmReadIdPfr0           // Read EL1 Processor Feature Register (PFR0)
   mov   x30, x1                 // Restore LR
-  ands  x0, x0, #AARCH64_PFR0_FP// Extract bits indicating VFP implementation
-  cmp   x0, #0                  // VFP is implemented if '0'.
-  b.ne  4f                      // Exit if VFP not implemented.
+  ubfx  x0, x0, #16, #4         // Extract the FP bits 16:19
+  cmp   x0, #0xF                // Check if FP bits are '1111b',
+                                // i.e. Floating Point not implemented
+  b.eq  4f                      // Exit when VFP is not implemented.
+
   // FVP is implemented.
   // Make sure VFP exceptions are not trapped (to any exception level).
   mrs   x0, cpacr_el1           // Read EL1 Coprocessor Access Control Register (CPACR)
-- 
Guid("CE165669-3EF3-493F-B85D-6190EE5B9759")