linux-kernel - Re: [PATCH] riscv: hwprobe: export Zihintpause ISA extension

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Message-ID: <3cd9c332-1187-4204-94c9-34a3c4f5958c@rivosinc.com>
Date: Tue, 20 Feb 2024 15:42:55 -0800
From: Atish Patra <atishp@...osinc.com>
To: Clément Léger <cleger@...osinc.com>,
 Jonathan Corbet <corbet@....net>, Paul Walmsley <paul.walmsley@...ive.com>,
 Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>,
 linux-doc@...r.kernel.org, linux-riscv@...ts.infradead.org,
 linux-kernel@...r.kernel.org
Cc: Robbin Ehn <rehn@...osinc.com>
Subject: Re: [PATCH] riscv: hwprobe: export Zihintpause ISA extension

On 2/19/24 07:49, Clément Léger wrote:
> Export the Zihintpause ISA extension through hwprobe which allows using
> "pause" instructions. Some userspace applications (OpenJDK for
> instance) uses this to handle some locking back-off.
> 
> Signed-off-by: Clément Léger <cleger@...osinc.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..0012c8433613 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_ZIHINTPAUSE`: The Zihintpause extension is
> +       supported as defined in the RISC-V ISA manual starting from commit commit
> +       d8ab5c78c207 ("Zihintpause is ratified").
> +
>   * :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..31c570cbd1c5 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_ZIHINTPAUSE	(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 a7c56b41efd2..1008d25880e1 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(ZIHINTPAUSE);
>   
>   		if (has_vector()) {
>   			EXT_KEY(ZVBB);

Reviewed-by: Atish Patra <atishp@...osinc.com>