linux-kernel - Re: [PATCH v3 1/2] riscv: hwprobe: Expose Zicbop extension and its block size

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Message-ID: <20251021-be53f84c246523b7c4e31917@orel>
Date: Tue, 21 Oct 2025 16:21:42 -0700
From: Andrew Jones <ajones@...tanamicro.com>
To: Yao Zihong <zihong.plct@...c.iscas.ac.cn>
Cc: alex@...ti.fr, alexghiti@...osinc.com, aou@...s.berkeley.edu, 
	cleger@...osinc.com, evan@...osinc.com, linux-kernel@...r.kernel.org, 
	linux-riscv@...ts.infradead.org, palmer@...belt.com, pjw@...nel.org, samuel.holland@...ive.com, 
	shuah@...nel.org, zhangyin2018@...as.ac.cn, zihongyao@...look.com
Subject: Re: [PATCH v3 1/2] riscv: hwprobe: Expose Zicbop extension and its
 block size

On Mon, Oct 20, 2025 at 11:33:08PM +0800, Yao Zihong wrote:
> - Add `RISCV_HWPROBE_EXT_ZICBOP` to report the presence of the
>   Zicbop extension.
> - Add `RISCV_HWPROBE_KEY_ZICBOP_BLOCK_SIZE` to expose the block
>   size (in bytes) when Zicbop is supported.
> - Update hwprobe.rst to document the new extension bit and block
>   size key, following the existing Zicbom/Zicboz style.
> 
> Signed-off-by: Yao Zihong <zihong.plct@...c.iscas.ac.cn>
> ---
>  Documentation/arch/riscv/hwprobe.rst  | 8 +++++++-
>  arch/riscv/include/asm/hwprobe.h      | 2 +-
>  arch/riscv/include/uapi/asm/hwprobe.h | 2 ++
>  arch/riscv/kernel/sys_hwprobe.c       | 6 ++++++
>  4 files changed, 16 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/arch/riscv/hwprobe.rst b/Documentation/arch/riscv/hwprobe.rst
> index 2f449c9b15bd..52f12af43b9d 100644
> --- a/Documentation/arch/riscv/hwprobe.rst
> +++ b/Documentation/arch/riscv/hwprobe.rst
> @@ -275,6 +275,9 @@ The following keys are defined:
>         ratified in commit 49f49c842ff9 ("Update to Rafified state") of
>         riscv-zabha.
>  
> +  * :c:macro:`RISCV_HWPROBE_EXT_ZICBOP`: The Zicbop extension is supported, as
> +       ratified in commit 3dd606f ("Create cmobase-v1.0.pdf") of riscv-CMOs.
> +
>  * :c:macro:`RISCV_HWPROBE_KEY_CPUPERF_0`: Deprecated.  Returns similar values to
>       :c:macro:`RISCV_HWPROBE_KEY_MISALIGNED_SCALAR_PERF`, but the key was
>       mistakenly classified as a bitmask rather than a value.
> @@ -369,4 +372,7 @@ The following keys are defined:
>  
>      * :c:macro:`RISCV_HWPROBE_VENDOR_EXT_XSFVFWMACCQQQ`: The Xsfvfwmaccqqq
>          vendor extension is supported in version 1.0 of Matrix Multiply Accumulate
> -	Instruction Extensions Specification.
> \ No newline at end of file
> +	Instruction Extensions Specification.
> +
> +* :c:macro:`RISCV_HWPROBE_KEY_ZICBOP_BLOCK_SIZE`: An unsigned int which
> +  represents the size of the Zicbop block in bytes.
> diff --git a/arch/riscv/include/asm/hwprobe.h b/arch/riscv/include/asm/hwprobe.h
> index 948d2b34e94e..2f278c395af9 100644
> --- a/arch/riscv/include/asm/hwprobe.h
> +++ b/arch/riscv/include/asm/hwprobe.h
> @@ -8,7 +8,7 @@
>  
>  #include <uapi/asm/hwprobe.h>
>  
> -#define RISCV_HWPROBE_MAX_KEY 14
> +#define RISCV_HWPROBE_MAX_KEY 15
>  
>  static inline bool riscv_hwprobe_key_is_valid(__s64 key)
>  {
> diff --git a/arch/riscv/include/uapi/asm/hwprobe.h b/arch/riscv/include/uapi/asm/hwprobe.h
> index 5d30a4fae37a..9cc508be54c5 100644
> --- a/arch/riscv/include/uapi/asm/hwprobe.h
> +++ b/arch/riscv/include/uapi/asm/hwprobe.h
> @@ -82,6 +82,7 @@ struct riscv_hwprobe {
>  #define		RISCV_HWPROBE_EXT_ZAAMO		(1ULL << 56)
>  #define		RISCV_HWPROBE_EXT_ZALRSC	(1ULL << 57)
>  #define		RISCV_HWPROBE_EXT_ZABHA		(1ULL << 58)
> +#define		RISCV_HWPROBE_EXT_ZICBOP	(1ULL << 59)
>  #define RISCV_HWPROBE_KEY_CPUPERF_0	5
>  #define		RISCV_HWPROBE_MISALIGNED_UNKNOWN	(0 << 0)
>  #define		RISCV_HWPROBE_MISALIGNED_EMULATED	(1 << 0)
> @@ -107,6 +108,7 @@ struct riscv_hwprobe {
>  #define RISCV_HWPROBE_KEY_ZICBOM_BLOCK_SIZE	12
>  #define RISCV_HWPROBE_KEY_VENDOR_EXT_SIFIVE_0	13
>  #define RISCV_HWPROBE_KEY_VENDOR_EXT_MIPS_0	14
> +#define RISCV_HWPROBE_KEY_ZICBOP_BLOCK_SIZE	15
>  /* Increase RISCV_HWPROBE_MAX_KEY when adding items. */
>  
>  /* Flags */
> diff --git a/arch/riscv/kernel/sys_hwprobe.c b/arch/riscv/kernel/sys_hwprobe.c
> index 000f4451a9d8..7a6ae1327504 100644
> --- a/arch/riscv/kernel/sys_hwprobe.c
> +++ b/arch/riscv/kernel/sys_hwprobe.c
> @@ -113,6 +113,7 @@ static void hwprobe_isa_ext0(struct riscv_hwprobe *pair,
>  		EXT_KEY(ZCB);
>  		EXT_KEY(ZCMOP);
>  		EXT_KEY(ZICBOM);
> +		EXT_KEY(ZICBOP);
>  		EXT_KEY(ZICBOZ);
>  		EXT_KEY(ZICNTR);
>  		EXT_KEY(ZICOND);
> @@ -293,6 +294,11 @@ static void hwprobe_one_pair(struct riscv_hwprobe *pair,
>  		if (hwprobe_ext0_has(cpus, RISCV_HWPROBE_EXT_ZICBOM))
>  			pair->value = riscv_cbom_block_size;
>  		break;
> +	case RISCV_HWPROBE_KEY_ZICBOP_BLOCK_SIZE:
> +		pair->value = 0;
> +		if (hwprobe_ext0_has(cpus, RISCV_HWPROBE_EXT_ZICBOP))
> +			pair->value = riscv_cbop_block_size;
> +		break;
>  	case RISCV_HWPROBE_KEY_HIGHEST_VIRT_ADDRESS:
>  		pair->value = user_max_virt_addr();
>  		break;
> -- 
> 2.47.2
>

Reviewed-by: Andrew Jones <ajones@...tanamicro.com>