[RFC 02/14] lib: sbi: Detect mcountinihibit support at runtime

[Anup Patel]

> -----Original Message-----
> From: Atish Patra <atish.patra at wdc.com>
> Sent: 20 March 2021 03:43
> To: opensbi at lists.infradead.org
> Cc: Atish Patra <Atish.Patra at wdc.com>; Anup Patel <Anup.Patel at wdc.com>
> Subject: [RFC 02/14] lib: sbi: Detect mcountinihibit support at runtime
> 
> RISC-V ISA specification v1.11 defined mcountinhibit CSR that allows software
> to stop any counter from incrementing. The SBI PMU extension depends on
> this CSR support in hardware.
> 
> Define mcountinhibit as a hart specific feature and detect it at runtime.
> 
> Signed-off-by: Atish Patra <atish.patra at wdc.com>
> ---
>  include/sbi/sbi_hart.h |  4 +++-
>  lib/sbi/sbi_hart.c     | 12 ++++++++++++
>  2 files changed, 15 insertions(+), 1 deletion(-)
> 
> diff --git a/include/sbi/sbi_hart.h b/include/sbi/sbi_hart.h index
> 031c7b08a815..9e317c52008c 100644
> --- a/include/sbi/sbi_hart.h
> +++ b/include/sbi/sbi_hart.h
> @@ -18,8 +18,10 @@ enum sbi_hart_features {
>  	SBI_HART_HAS_SCOUNTEREN = (1 << 0),
>  	/** Hart has M-mode counter enable */
>  	SBI_HART_HAS_MCOUNTEREN = (1 << 1),
> +	/** Hart has counter inhibit CSR */
> +	SBI_HART_HAS_MCOUNTINHIBIT = (1 << 2),
>  	/** HART has timer csr implementation in hardware */
> -	SBI_HART_HAS_TIME = (1 << 2),
> +	SBI_HART_HAS_TIME = (1 << 3),
> 
>  	/** Last index of Hart features*/
>  	SBI_HART_HAS_LAST_FEATURE = SBI_HART_HAS_TIME, diff --git
> a/lib/sbi/sbi_hart.c b/lib/sbi/sbi_hart.c index d91b08cf1cec..0b3bb6237182
> 100644
> --- a/lib/sbi/sbi_hart.c
> +++ b/lib/sbi/sbi_hart.c
> @@ -259,6 +259,9 @@ static inline char
> *sbi_hart_feature_id2string(unsigned long feature)
>  	case SBI_HART_HAS_MCOUNTEREN:
>  		fstr = "mcounteren";
>  		break;
> +	case SBI_HART_HAS_MCOUNTINHIBIT:
> +		fstr = "mcountinhibit";
> +		break;
>  	case SBI_HART_HAS_TIME:
>  		fstr = "time";
>  		break;
> @@ -423,6 +426,15 @@ __mhpm_skip:
>  			hfeatures->features |=
> SBI_HART_HAS_MCOUNTEREN;
>  	}
> 
> +	/* Detect if hart supports MCOUNTINHIBIT feature */
> +	trap.cause = 0;

Don't need to set trap.cause here anymore.

> +	val = csr_read_allowed(CSR_MCOUNTINHIBIT, (unsigned
> long)&trap);
> +	if (!trap.cause) {
> +		csr_write_allowed(CSR_MCOUNTINHIBIT, (unsigned
> long)&trap, val);
> +		if (!trap.cause)
> +			hfeatures->features |=
> SBI_HART_HAS_MCOUNTINHIBIT;
> +	}
> +
>  	/* Detect if hart supports time CSR */
>  	trap.cause = 0;
>  	csr_read_allowed(CSR_TIME, (unsigned long)&trap);
> --
> 2.25.1

Apart from above, looks good to me.

Reviewed-by: Anup Patel <anup.patel at wdc.com>

Regards,
Anup