[RFC PATCH 3/9] lib:sbi: Detect SSCOF extension at run time

[Anup Patel]

On Fri, Sep 10, 2021 at 2:10 AM Atish Patra <atish.patra at wdc.com> wrote:
>
> SSCOF ISA extension introduces PMU counter overflow and filtering support.
> It introduces a read only `scountovf` csr that can be used to detect if
> a hart supports this extension at runtime. However, this feature is only
> useful if the hart already supports mcounteren and mcountinhibit.
>
> Add a dynamic detection mechanism and boot time print message if sscof
> is present.
>
> Signed-off-by: Atish Patra <atish.patra at wdc.com>

Looks good to me.

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

Regards,
Anup

> ---
>  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 0c18ef9325b2..580a7989a4de 100644
> --- a/include/sbi/sbi_hart.h
> +++ b/include/sbi/sbi_hart.h
> @@ -20,8 +20,10 @@ enum sbi_hart_features {
>         SBI_HART_HAS_MCOUNTEREN = (1 << 1),
>         /** Hart has counter inhibit CSR */
>         SBI_HART_HAS_MCOUNTINHIBIT = (1 << 2),
> +       /** Hart has sscofpmf extension */
> +       SBI_HART_HAS_SSCOF = (1 << 3),
>         /** HART has timer csr implementation in hardware */
> -       SBI_HART_HAS_TIME = (1 << 3),
> +       SBI_HART_HAS_TIME = (1 << 4),
>
>         /** 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 6254452e11bb..44b8dfd1b551 100644
> --- a/lib/sbi/sbi_hart.c
> +++ b/lib/sbi/sbi_hart.c
> @@ -288,6 +288,9 @@ static inline char *sbi_hart_feature_id2string(unsigned long feature)
>         case SBI_HART_HAS_MCOUNTINHIBIT:
>                 fstr = "mcountinhibit";
>                 break;
> +       case SBI_HART_HAS_SSCOF:
> +               fstr = "sscof";
> +               break;
>         case SBI_HART_HAS_TIME:
>                 fstr = "time";
>                 break;
> @@ -497,6 +500,15 @@ __mhpm_skip:
>                         hfeatures->features |= SBI_HART_HAS_MCOUNTINHIBIT;
>         }
>
> +       /* Counter overflow/filtering is not useful without mcounter/inhibit */
> +       if (hfeatures->features & SBI_HART_HAS_MCOUNTINHIBIT &&
> +           hfeatures->features & SBI_HART_HAS_MCOUNTEREN) {
> +               /* Detect if hart supports sscofpmf */
> +               csr_read_allowed(CSR_SCOUNTOVF, (unsigned long)&trap);
> +               if (!trap.cause)
> +                       hfeatures->features |= SBI_HART_HAS_SSCOF;
> +       }
> +
>         /* Detect if hart supports time CSR */
>         csr_read_allowed(CSR_TIME, (unsigned long)&trap);
>         if (!trap.cause)
> --
> 2.31.1
>
>
> --
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