Re: [PATCH 1/5] riscv: Checksum header

Conor Dooley
2023-08-27T01:42:53Z

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On Sat, Aug 26, 2023 at 06:26:06PM -0700, Charlie Jenkins wrote:
> Provide checksum algorithms that have been designed to leverage riscv
> instructions such as rotate. In 64-bit, can take advantage of the larger
> register to avoid some overflow checking.
>
> Add configuration for Zba extension and add march for Zba and Zbb.
>
> Signed-off-by: Charlie Jenkins <charlie@rivosinc.com>
> ---
> arch/riscv/Kconfig | 23 +++++++++++
> arch/riscv/Makefile | 2 +
> arch/riscv/include/asm/checksum.h | 86 +++++++++++++++++++++++++++++++++++++++
> 3 files changed, 111 insertions(+)
>
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index 4c07b9189c86..8d7e475ca28d 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -507,6 +507,29 @@ config RISCV_ISA_V_DEFAULT_ENABLE
>
> 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 || $(cc-option,-mabi=ilp32 -march=rv32ima_zba)
> + depends on LLD_VERSION >= 150000 || LD_VERSION >= 23900
> + depends on AS_HAS_OPTION_ARCH
> +
> +config RISCV_ISA_ZBA
> + bool "Zba extension support for bit manipulation instructions"
> + depends on TOOLCHAIN_HAS_ZBA
> + depends on MMU
> + depends on RISCV_ALTERNATIVE
> + default y
> + help
> + Adds support to dynamically detect the presence of the ZBA
> + extension (basic bit manipulation) and enable its usage.
> +
> + The Zba extension provides instructions to accelerate a number
> + of bit-specific address creation operations.
> +
> + If you don't know what to do here, say Y.
> +
> config TOOLCHAIN_HAS_ZBB
> bool
> default y
> diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
> index 6ec6d52a4180..51fa3f67fc9a 100644
> --- a/arch/riscv/Makefile
> +++ b/arch/riscv/Makefile
> @@ -61,6 +61,8 @@ riscv-march-$(CONFIG_ARCH_RV64I) := rv64ima
> riscv-march-$(CONFIG_FPU) := $(riscv-march-y)fd
> riscv-march-$(CONFIG_RISCV_ISA_C) := $(riscv-march-y)c
> riscv-march-$(CONFIG_RISCV_ISA_V) := $(riscv-march-y)v
> +riscv-march-$(CONFIG_RISCV_ISA_ZBA) := $(riscv-march-y)_zba
> +riscv-march-$(CONFIG_RISCV_ISA_ZBB) := $(riscv-march-y)_zbb

AFAICT, this is going to break immediately on any system that enables
RISCV_ISA_ZBA (which will happen by default) but does not support the
extension. You made the option depend on RISCV_ALTERNATIVE, but I do
not see any use of alternatives in the code to actually perform the
dynamic detection of Zba.
Note that for fd & v, we add it to riscv-march-y, but then immediately
remove it again before passing to the compiler, only allow them in
AFLAGS:
# Remove F,D,V from isa string for all. Keep extensions between "fd" and "v" by
# matching non-v and non-multi-letter extensions out with the filter ([^v_]*)
KBUILD_CFLAGS += -march=$(shell echo $(riscv-march-y) | sed -E 's/(rv32ima|rv64ima)fd([^v_]*)v?/\1\2/')

What am I missing?

Thanks,
Conor.

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