[PATCH v2 6/8] riscv: Add PLATFORM_SUPPORTS_RISCV_ISA_ZBA Kconfig option

[Charlie Jenkins]

Zba can optimize kernel instruction sequences. Add a config option
PLATFORM_SUPPORTS_RISCV_ISA_ZBA that allows arbitrary Zba instruction
sequences to be emitted by the compiler.

The existing "RISCV_ISA_ZBA" option is repurposed to be used to by kernel
code to determine if either PLATFORM_MAY_SUPPORT_RISCV_ISA_ZBA or
PLATFORM_SUPPORTS_RISCV_ISA_ZBA has been set.

Signed-off-by: Charlie Jenkins <charlie at rivosinc.com>
---
 arch/riscv/Kconfig.isa | 52 ++++++++++++++++++++++++++++++++++++++++++++++++++
 arch/riscv/Makefile    |  1 +
 2 files changed, 53 insertions(+)

diff --git a/arch/riscv/Kconfig.isa b/arch/riscv/Kconfig.isa
index 49bed8c75263..e7f28dc44137 100644
--- a/arch/riscv/Kconfig.isa
+++ b/arch/riscv/Kconfig.isa
@@ -186,6 +186,58 @@ config PLATFORM_MAY_SUPPORT_RISCV_ISA_SVPBMT
 
 	   If you don't know what to do here, say Y.
 
+
+config TOOLCHAIN_HAS_ZBA
+	bool
+	default y
+	depends on !64BIT || $(cc-option,-mabi=lp64 -march=rv64ima_zba)
+	depends on !32BIT || $(cc-option,-mabi=ilp32 -march=rv32ima_zba)
+	depends on LLD_VERSION >= 150000 || LD_VERSION >= 23900
+	depends on AS_HAS_OPTION_ARCH
+
+config RISCV_ISA_ZBA
+	bool
+
+choice
+	prompt "Zba extension for address generation instructions support"
+	default PLATFORM_MAY_SUPPORT_RISCV_ISA_ZBA
+	help
+	  This selects the level of support for Zba instructions to be
+	  built into the Linux Kernel. This does not impact whether Zba
+	  instructions are allowed to be emitted by user-space code.
+
+	  The Zba extension provides instructions to accelerate a number
+	  of address generation instruction sequences.
+
+config PROHIBIT_RISCV_ISA_ZBA
+	bool "Prohibit Zba instruction sequences"
+	depends on NONPORTABLE
+	help
+	  Regardless of if the platform supports Zba instructions,
+	  prohibit the kernel from emitting Zba instructions.
+
+config PLATFORM_MAY_SUPPORT_RISCV_ISA_ZBA
+	bool "Allow Zba instruction sequences if supported"
+	depends on TOOLCHAIN_HAS_ZBB
+	depends on RISCV_ALTERNATIVE
+	select RISCV_ISA_ZBA
+	help
+	  Add support for enabling optimisations in the kernel when the
+	  Zba extension is detected at boot.
+
+config PLATFORM_SUPPORTS_RISCV_ISA_ZBA
+	bool "Emit Zba instructions when building Linux"
+	depends on TOOLCHAIN_HAS_ZBB
+	depends on NONPORTABLE
+	select RISCV_ISA_ZBA
+	help
+	  Adds "zba" to the ISA subsets that the toolchain is allowed to emit
+	  when building Linux, which results in Zba instructions in the
+	  Linux binary. This option produces a kernel that will not run on
+	  systems that do not support the Zba extension.
+
+endchoice
+
 config TOOLCHAIN_HAS_ZBB
 	bool
 	default y
diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
index 6b0c3a782f99..c8ec38b9880a 100644
--- a/arch/riscv/Makefile
+++ b/arch/riscv/Makefile
@@ -66,6 +66,7 @@ riscv-march-$(CONFIG_ARCH_RV32I)	:= rv32ima
 riscv-march-$(CONFIG_ARCH_RV64I)	:= rv64ima
 riscv-march-$(CONFIG_FPU)		:= $(riscv-march-y)fd
 riscv-march-$(CONFIG_PLATFORM_SUPPORTS_RISCV_ISA_C)	:= $(riscv-march-y)c
+riscv-march-$(CONFIG_PLATFORM_SUPPORTS_RISCV_ISA_ZBA)	:= $(riscv-march-y)_zba
 riscv-march-$(CONFIG_PLATFORM_SUPPORTS_RISCV_ISA_ZBB)	:= $(riscv-march-y)_zbb
 
 ifdef CONFIG_TOOLCHAIN_NEEDS_OLD_ISA_SPEC

-- 
2.44.0