linux-kernel - Re: [PATCH v4 2/3] RISC-V: hwprobe: Expose Zicbom extension and its block size

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Message-ID: <7c181d03-b0d0-4b81-bbd0-06943a58a287@sifive.com>
Date: Mon, 13 Jan 2025 23:28:20 -0600
From: Samuel Holland <samuel.holland@...ive.com>
To: Yunhui Cui <cuiyunhui@...edance.com>
Cc: ajones@...tanamicro.com, alexghiti@...osinc.com, andybnac@...il.com,
 aou@...s.berkeley.edu, charlie@...osinc.com, cleger@...osinc.com,
 conor.dooley@...rochip.com, conor@...nel.org, corbet@....net,
 evan@...osinc.com, jesse@...osinc.com, linux-doc@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
 linux-riscv@...ts.infradead.org, palmer@...belt.com,
 paul.walmsley@...ive.com, shuah@...nel.org
Subject: Re: [PATCH v4 2/3] RISC-V: hwprobe: Expose Zicbom extension and its
 block size

Hi Yunhui,

On 2025-01-13 8:19 PM, Yunhui Cui wrote:
> Expose Zicbom through hwprobe and also provide a key to extract its
> respective block size.
> 
> Signed-off-by: Yunhui Cui <cuiyunhui@...edance.com>
> ---
>  Documentation/arch/riscv/hwprobe.rst  | 6 ++++++
>  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, 15 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/arch/riscv/hwprobe.rst b/Documentation/arch/riscv/hwprobe.rst
> index 955fbcd19ce9..0ea7754b2049 100644
> --- a/Documentation/arch/riscv/hwprobe.rst
> +++ b/Documentation/arch/riscv/hwprobe.rst
> @@ -242,6 +242,9 @@ The following keys are defined:
>    * :c:macro:`RISCV_HWPROBE_EXT_SUPM`: The Supm extension is supported as
>         defined in version 1.0 of the RISC-V Pointer Masking extensions.
>  
> +  * :c:macro:`RISCV_HWPROBE_EXT_ZICBOM`: The Zicbom 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.
> @@ -281,6 +284,9 @@ The following keys are defined:
>  * :c:macro:`RISCV_HWPROBE_KEY_MISALIGNED_VECTOR_PERF`: An enum value describing the
>       performance of misaligned vector accesses on the selected set of processors.
>  
> +* :c:macro:`RISCV_HWPROBE_KEY_ZICBOM_BLOCK_SIZE`: An unsigned int which
> +  represents the size of the Zicbom block in bytes.
> +
>    * :c:macro:`RISCV_HWPROBE_MISALIGNED_VECTOR_UNKNOWN`: The performance of misaligned
>      vector accesses is unknown.

The new key needs to go further down, below this list of possible values for the
previous key.

Regards,
Samuel

>  
> diff --git a/arch/riscv/include/asm/hwprobe.h b/arch/riscv/include/asm/hwprobe.h
> index 1ce1df6d0ff3..89379f9a2e6e 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 10
> +#define RISCV_HWPROBE_MAX_KEY 11
>  
>  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 3af142b99f77..b15c0bd83ef2 100644
> --- a/arch/riscv/include/uapi/asm/hwprobe.h
> +++ b/arch/riscv/include/uapi/asm/hwprobe.h
> @@ -73,6 +73,7 @@ struct riscv_hwprobe {
>  #define		RISCV_HWPROBE_EXT_ZCMOP		(1ULL << 47)
>  #define		RISCV_HWPROBE_EXT_ZAWRS		(1ULL << 48)
>  #define		RISCV_HWPROBE_EXT_SUPM		(1ULL << 49)
> +#define		RISCV_HWPROBE_EXT_ZICBOM	(1ULL << 50)
>  #define RISCV_HWPROBE_KEY_CPUPERF_0	5
>  #define		RISCV_HWPROBE_MISALIGNED_UNKNOWN	(0 << 0)
>  #define		RISCV_HWPROBE_MISALIGNED_EMULATED	(1 << 0)
> @@ -94,6 +95,7 @@ struct riscv_hwprobe {
>  #define		RISCV_HWPROBE_MISALIGNED_VECTOR_SLOW		2
>  #define		RISCV_HWPROBE_MISALIGNED_VECTOR_FAST		3
>  #define		RISCV_HWPROBE_MISALIGNED_VECTOR_UNSUPPORTED	4
> +#define RISCV_HWPROBE_KEY_ZICBOM_BLOCK_SIZE	11
>  /* 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 cb93adfffc48..04150e62f998 100644
> --- a/arch/riscv/kernel/sys_hwprobe.c
> +++ b/arch/riscv/kernel/sys_hwprobe.c
> @@ -106,6 +106,7 @@ static void hwprobe_isa_ext0(struct riscv_hwprobe *pair,
>  		EXT_KEY(ZCA);
>  		EXT_KEY(ZCB);
>  		EXT_KEY(ZCMOP);
> +		EXT_KEY(ZICBOM);
>  		EXT_KEY(ZICBOZ);
>  		EXT_KEY(ZICOND);
>  		EXT_KEY(ZIHINTNTL);
> @@ -278,6 +279,11 @@ static void hwprobe_one_pair(struct riscv_hwprobe *pair,
>  		if (hwprobe_ext0_has(cpus, RISCV_HWPROBE_EXT_ZICBOZ))
>  			pair->value = riscv_cboz_block_size;
>  		break;
> +	case RISCV_HWPROBE_KEY_ZICBOM_BLOCK_SIZE:
> +		pair->value = 0;
> +		if (hwprobe_ext0_has(cpus, RISCV_HWPROBE_EXT_ZICBOM))
> +			pair->value = riscv_cbom_block_size;
> +		break;
>  	case RISCV_HWPROBE_KEY_HIGHEST_VIRT_ADDRESS:
>  		pair->value = user_max_virt_addr();
>  		break;