arm64: Add framework for legacy instruction emulation

Typically, providing support for legacy instructions requires
emulating the behaviour of instructions whose encodings have become
undefined. If the instructions haven't been removed from the
architecture, there maybe an option in the implementation to turn
on/off the support for these instructions.

Create common infrastructure to support legacy instruction
emulation. In addition to emulation, also provide an option to support
hardware execution when supported. The default execution mode (one of
undef, emulate, hw exeuction) is dependent on the state of the
instruction (deprecated or obsolete) in the architecture and
can specified at the time of registering the instruction handlers. The
runtime state of the emulation can be controlled by writing to
individual nodes in sysctl. The expected default behaviour is
documented as part of this patch.

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>

1 files changed, 18 insertions, 0 deletions

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 1e0e4671dd25..aa8f4bea3738 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -164,6 +164,24 @@ config ARCH_XGENE
         help
           This enables support for AppliedMicro X-Gene SOC Family
 
+comment "Processor Features"
+
+menuconfig ARMV8_DEPRECATED
+        bool "Emulate deprecated/obsolete ARMv8 instructions"
+        depends on COMPAT
+        help
+          Legacy software support may require certain instructions
+          that have been deprecated or obsoleted in the architecture.
+
+          Enable this config to enable selective emulation of these
+          features.
+
+          If unsure, say Y
+
+if ARMV8_DEPRECATED
+
+endif
+
 endmenu
 
 menu "Bus support"