arm64: Port SWP/SWPB emulation support from arm
The SWP instruction was deprecated in the ARMv6 architecture. The
ARMv7 multiprocessing extensions mandate that SWP/SWPB instructions
are treated as undefined from reset, with the ability to enable them
through the System Control Register SW bit. With ARMv8, the option to
enable these instructions through System Control Register was dropped
as well.
To support legacy applications using these instructions, port the
emulation of the SWP and SWPB instructions from the arm port to arm64.
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Punit Agrawal <punit.agrawal@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
diff --git a/Documentation/arm64/legacy_instructions.txt b/Documentation/arm64/legacy_instructions.txt
index 49d4867..5ab5861 100644
--- a/Documentation/arm64/legacy_instructions.txt
+++ b/Documentation/arm64/legacy_instructions.txt
@@ -31,3 +31,10 @@
The default mode depends on the status of the instruction in the
architecture. Deprecated instructions should default to emulation
while obsolete instructions must be undefined by default.
+
+Supported legacy instructions
+-----------------------------
+* SWP{B}
+Node: /proc/sys/abi/swp
+Status: Obsolete
+Default: Undef (0)