[PATCH v2 1/2] lib: sbi: hart: Detect existence of cycle and instret CSRs for Zicntr

[Xiang W]

在 2025-04-18五的 14:47 +0000，Yao Zi写道：
> Zicntr extension specifies three read-only CSRs, time, cycle and
> instret. It isn't sufficient to report Zicntr is fully supported with
> only time CSR detected.
> 
> This patch introduces a bitmap to sbi_hart_features to record
> availability of these CSRs, which are detected using traps. Zicntr is
> reported as present if and only if three CSRs are all available on the
> HARTs.
> 
> Suggested-by: Anup Patel <anup at brainfault.org>
> Signed-off-by: Yao Zi <ziyao at disroot.org>
> ---
>  include/sbi/sbi_hart.h |  9 +++++++++
>  lib/sbi/sbi_hart.c     | 35 ++++++++++++++++++++++++++++-------
>  2 files changed, 37 insertions(+), 7 deletions(-)
> 
> diff --git a/include/sbi/sbi_hart.h b/include/sbi/sbi_hart.h
> index c3a7feb..48edafe 100644
> --- a/include/sbi/sbi_hart.h
> +++ b/include/sbi/sbi_hart.h
> @@ -91,6 +91,13 @@ struct sbi_hart_ext_data {
>  
>  extern const struct sbi_hart_ext_data sbi_hart_ext[];
>  
> +/** CSRs should be detected by access and trapping */
> +enum sbi_hart_csrs {
> +	SBI_HART_CSR_CYCLE = 0,
> +	SBI_HART_CSR_TIME,
> +	SBI_HART_CSR_INSTRET,
add SBI_HART_CSR_MAX
> +};
> +
>  /*
>   * Smepmp enforces access boundaries between M-mode and
>   * S/U-mode. When it is enabled, the PMPs are programmed
> @@ -110,6 +117,7 @@ struct sbi_hart_features {
>  	bool detected;
>  	int priv_version;
>  	unsigned long extensions[BITS_TO_LONGS(SBI_HART_EXT_MAX)];
> +	unsigned long csrs;
change to unsigned long csrs[BITS_TO_LONGS(SBI_HART_CSR_MAX)];

To make the code more flexible, it is recommended to add the above modification

Regards,
Xiang W
>  	unsigned int pmp_count;
>  	unsigned int pmp_addr_bits;
>  	unsigned int pmp_log2gran;
> @@ -148,6 +156,7 @@ bool sbi_hart_has_extension(struct sbi_scratch *scratch,
>  			    enum sbi_hart_extensions ext);
>  void sbi_hart_get_extensions_str(struct sbi_scratch *scratch,
>  				 char *extension_str, int nestr);
> +bool sbi_hart_has_csr(struct sbi_scratch *scratch, enum sbi_hart_csrs csr);
>  
>  void __attribute__((noreturn)) sbi_hart_hang(void);
>  
> diff --git a/lib/sbi/sbi_hart.c b/lib/sbi/sbi_hart.c
> index c343805..f98b6b0 100644
> --- a/lib/sbi/sbi_hart.c
> +++ b/lib/sbi/sbi_hart.c
> @@ -733,6 +733,20 @@ void sbi_hart_get_extensions_str(struct sbi_scratch *scratch,
>  		sbi_strncpy(extensions_str, "none", nestr);
>  }
>  
> +/**
> + * Check whether a particular CSR is present on the HART
> + *
> + * @param scratch pointer to the HART scratch space
> + * @param csr the CSR number to check
> + */
> +bool sbi_hart_has_csr(struct sbi_scratch *scratch, enum sbi_hart_csrs csr)
> +{
> +	struct sbi_hart_features *hfeatures =
> +			sbi_scratch_offset_ptr(scratch, hart_features_offset);
> +
> +	return (hfeatures->csrs >> csr) & 1UL;
> +}
> +
>  static unsigned long hart_pmp_get_allowed_addr(void)
>  {
>  	unsigned long val = 0;
> @@ -789,7 +803,6 @@ static int hart_detect_features(struct sbi_scratch *scratch)
>  	struct sbi_hart_features *hfeatures =
>  		sbi_scratch_offset_ptr(scratch, hart_features_offset);
>  	unsigned long val, oldval;
> -	bool has_zicntr = false;
>  	int rc;
>  
>  	/* If hart features already detected then do nothing */
> @@ -798,6 +811,7 @@ static int hart_detect_features(struct sbi_scratch *scratch)
>  
>  	/* Clear hart features */
>  	sbi_memset(hfeatures->extensions, 0, sizeof(hfeatures->extensions));
> +	hfeatures->csrs = 0;
>  	hfeatures->pmp_count = 0;
>  	hfeatures->mhpm_mask = 0;
>  	hfeatures->priv_version = SBI_HART_PRIV_VER_UNKNOWN;
> @@ -924,9 +938,6 @@ __pmp_skip:
>  	/* Detect if hart supports sscofpmf */
>  	__check_ext_csr(SBI_HART_PRIV_VER_1_11,
>  			CSR_SCOUNTOVF, SBI_HART_EXT_SSCOFPMF);
> -	/* Detect if hart supports time CSR */
> -	__check_ext_csr(SBI_HART_PRIV_VER_UNKNOWN,
> -			CSR_TIME, SBI_HART_EXT_ZICNTR);
>  	/* Detect if hart has AIA local interrupt CSRs */
>  	__check_ext_csr(SBI_HART_PRIV_VER_UNKNOWN,
>  			CSR_MTOPI, SBI_HART_EXT_SMAIA);
> @@ -945,8 +956,16 @@ __pmp_skip:
>  
>  #undef __check_ext_csr
>  
> -	/* Save trap based detection of Zicntr */
> -	has_zicntr = sbi_hart_has_extension(scratch, SBI_HART_EXT_ZICNTR);
> +#define __check_csr_existence(__csr, __csr_id)				\
> +	csr_read_allowed(__csr, &trap);					\
> +	if (!trap.cause)						\
> +		hfeatures->csrs |= 1 << __csr_id;
> +
> +	__check_csr_existence(CSR_CYCLE, SBI_HART_CSR_CYCLE);
> +	__check_csr_existence(CSR_TIME, SBI_HART_CSR_TIME);
> +	__check_csr_existence(CSR_INSTRET, SBI_HART_CSR_INSTRET);
> +
> +#undef __check_csr_existence
>  
>  	/* Let platform populate extensions */
>  	rc = sbi_platform_extensions_init(sbi_platform_thishart_ptr(),
> @@ -956,7 +975,9 @@ __pmp_skip:
>  
>  	/* Zicntr should only be detected using traps */
>  	__sbi_hart_update_extension(hfeatures, SBI_HART_EXT_ZICNTR,
> -				    has_zicntr);
> +			    (hfeatures->csrs & BIT(SBI_HART_CSR_CYCLE))	&&
> +			    (hfeatures->csrs & BIT(SBI_HART_CSR_TIME))	&&
> +			    (hfeatures->csrs & BIT(SBI_HART_CSR_INSTRET)));
>  
>  	/* Extensions implied by other extensions and features */
>  	if (hfeatures->mhpm_mask)
> -- 
> 2.49.0
>