[PATCH v3 4/6] riscv: hwprobe: export Zawrs ISA extension

[Clément Léger]

On 26/04/2024 12:08, Andrew Jones wrote:
> Export Zawrs ISA extension through hwprobe.
> 
> Signed-off-by: Andrew Jones <ajones at ventanamicro.com>
> ---
>  Documentation/arch/riscv/hwprobe.rst  | 4 ++++
>  arch/riscv/include/uapi/asm/hwprobe.h | 1 +
>  arch/riscv/kernel/sys_hwprobe.c       | 1 +
>  3 files changed, 6 insertions(+)
> 
> diff --git a/Documentation/arch/riscv/hwprobe.rst b/Documentation/arch/riscv/hwprobe.rst
> index b2bcc9eed9aa..e072ce8285d8 100644
> --- a/Documentation/arch/riscv/hwprobe.rst
> +++ b/Documentation/arch/riscv/hwprobe.rst
> @@ -188,6 +188,10 @@ The following keys are defined:
>         manual starting from commit 95cf1f9 ("Add changes requested by Ved
>         during signoff")
>  
> +  * :c:macro:`RISCV_HWPROBE_EXT_ZAWRS`: The Zawrs extension is supported as
> +       ratified in commit 98918c844281 ("Merge pull request #1217 from
> +       riscv/zawrs") of riscv-isa-manual.
> +
>  * :c:macro:`RISCV_HWPROBE_KEY_CPUPERF_0`: A bitmask that contains performance
>    information about the selected set of processors.
>  
> diff --git a/arch/riscv/include/uapi/asm/hwprobe.h b/arch/riscv/include/uapi/asm/hwprobe.h
> index 9f2a8e3ff204..a5fca3878a32 100644
> --- a/arch/riscv/include/uapi/asm/hwprobe.h
> +++ b/arch/riscv/include/uapi/asm/hwprobe.h
> @@ -59,6 +59,7 @@ struct riscv_hwprobe {
>  #define		RISCV_HWPROBE_EXT_ZTSO		(1ULL << 33)
>  #define		RISCV_HWPROBE_EXT_ZACAS		(1ULL << 34)
>  #define		RISCV_HWPROBE_EXT_ZICOND	(1ULL << 35)
> +#define		RISCV_HWPROBE_EXT_ZAWRS		(1ULL << 36)
>  #define RISCV_HWPROBE_KEY_CPUPERF_0	5
>  #define		RISCV_HWPROBE_MISALIGNED_UNKNOWN	(0 << 0)
>  #define		RISCV_HWPROBE_MISALIGNED_EMULATED	(1 << 0)
> diff --git a/arch/riscv/kernel/sys_hwprobe.c b/arch/riscv/kernel/sys_hwprobe.c
> index 8cae41a502dd..b86e3531a45a 100644
> --- a/arch/riscv/kernel/sys_hwprobe.c
> +++ b/arch/riscv/kernel/sys_hwprobe.c
> @@ -111,6 +111,7 @@ static void hwprobe_isa_ext0(struct riscv_hwprobe *pair,
>  		EXT_KEY(ZTSO);
>  		EXT_KEY(ZACAS);
>  		EXT_KEY(ZICOND);
> +		EXT_KEY(ZAWRS);
>  
>  		if (has_vector()) {
>  			EXT_KEY(ZVBB);

AFAIU, when used in userspace, this will actually "stall" the processor
until an interrupt/timeout happens, so the current process will keep
occupying the processor doing nothing (up to the next interrupt/timeout)
right ?

BTW, the spec also states that "When the TW (Timeout Wait) bit in
mstatus is set and WRS.NTO is executed in any privilege mode other than
M mode, and it does not complete within an implementation-specific
bounded time limit, the WRS.NTO instruction will cause an illegal
instruction exception." so I guess the process will be killed in this case ?

If this is not a concern:

Reviewed-by: Clément Léger <cleger at rivosinc.com>

Thanks,

Clément