riscv: Introduce support for defining instructions

When compiling with toolchains that haven't yet been taught about
new instructions we need to encode them ourselves. Create a new file
where support for instruction definitions will evolve. We initiate
the file with a macro called INSN_R(), which implements the R-type
instruction encoding. INSN_R() will use the assembler's .insn
directive when available, which should give the assembler a chance
to do some validation. When .insn is not available we fall back to
manual encoding.

Not only should using instruction encoding macros improve readability
and maintainability of code over the alternative of inserting
instructions directly (e.g. '.word 0xc0de'), but we should also gain
potential for more optimized code after compilation because the
compiler will have control over the input and output registers used.

Signed-off-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
Signed-off-by: Anup Patel <anup@brainfault.org>

1 files changed, 3 insertions, 0 deletions

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 59d18881f35b..d6b0ffd9bf00 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -227,6 +227,9 @@ config RISCV_DMA_NONCOHERENT
 	select ARCH_HAS_SETUP_DMA_OPS
 	select DMA_DIRECT_REMAP
 
+config AS_HAS_INSN
+	def_bool $(as-instr,.insn r 51$(comma) 0$(comma) 0$(comma) t0$(comma) t0$(comma) zero)
+
 source "arch/riscv/Kconfig.socs"
 source "arch/riscv/Kconfig.erratas"