[PATCH 1/1] lib: sbi: Add Smrnmi extension detection

[Anup Patel]

On Tue, Apr 30, 2024 at 2:13 PM Nylon Chen <nylon.chen at sifive.com> wrote:
>
> Adds detection and initialization of the Smrnmi extension
> in the SBI hart initialization code.
>
> The Smrnmi extension provides resumable non-maskable interrupts (RNMIs)
> support. It adds new CSRs (mnscratch, mnepc, mncause, mnstatus) to save
> the interrupted context and a new instruction MNRET to resume from the
> RNMI handler[1].
>
> we need to detect its presence and enable it in the early hart
> initialization process, before any traps.
>
> [1] https://github.com/riscv/riscv-isa-manual/blob/main/src/rnmi.adoc
>
> Co-developed-by: Zong Li <zong.li at sifive.com>
> Signed-off-by: Zong Li <zong.li at sifive.com>
> Signed-off-by: Nylon Chen <nylon.chen at sifive.com>
> Reviewed-by: Greentime Hu <greentime.hu at sifive.com>
> Reviewed-by: Yong-Xuan Wang <yongxuan.wang at sifive.com>
> ---
>  include/sbi/riscv_encoding.h | 10 ++++++++++
>  include/sbi/sbi_hart.h       |  2 ++
>  lib/sbi/sbi_hart.c           | 22 ++++++++++++++++++++++
>  3 files changed, 34 insertions(+)
>
> diff --git a/include/sbi/riscv_encoding.h b/include/sbi/riscv_encoding.h
> index d914828..320bb2b 100644
> --- a/include/sbi/riscv_encoding.h
> +++ b/include/sbi/riscv_encoding.h
> @@ -207,6 +207,10 @@
>
>  #endif
>
> +#define MNSTATUS_NMIE                  (_UL(0x8))
> +#define MNSTATUS_MNPV                  (_UL(0x80))
> +#define MNSTATUS_MNPP                  (_UL(0x1800))
> +
>  #define MHPMEVENT_SSCOF_MASK           _ULL(0xFFFF000000000000)
>
>  #define ENVCFG_STCE                    (_ULL(1) << 63)
> @@ -738,6 +742,12 @@
>  #define CSR_MSTATEEN3                  0x30F
>  #define CSR_MSTATEEN3H                 0x31F
>
> +/* Smrnmi extension registers */
> +#define CSR_MNSCRATCH                  0x740
> +#define CSR_MNEPC                      0x741
> +#define CSR_MNCAUSE                    0x742
> +#define CSR_MNSTATUS                   0x744
> +
>  /* Machine-Level High-Half CSRs (AIA) */
>  #define CSR_MIDELEGH                   0x313
>  #define CSR_MIEH                       0x314
> diff --git a/include/sbi/sbi_hart.h b/include/sbi/sbi_hart.h
> index cc78eec..d49d987 100644
> --- a/include/sbi/sbi_hart.h
> +++ b/include/sbi/sbi_hart.h
> @@ -63,6 +63,8 @@ enum sbi_hart_extensions {
>         SBI_HART_EXT_SSCSRIND,
>         /** Hart has Ssccfg extension */
>         SBI_HART_EXT_SSCCFG,
> +       /** Hart has Smrnmi extension */
> +       SBI_HART_EXT_SMRNMI,
>
>         /** Maximum index of Hart extension */
>         SBI_HART_EXT_MAX,
> diff --git a/lib/sbi/sbi_hart.c b/lib/sbi/sbi_hart.c
> index 0e7b5d1..6941a94 100644
> --- a/lib/sbi/sbi_hart.c
> +++ b/lib/sbi/sbi_hart.c
> @@ -668,6 +668,7 @@ const struct sbi_hart_ext_data sbi_hart_ext[] = {
>         __SBI_HART_EXT_DATA(smcdeleg, SBI_HART_EXT_SMCDELEG),
>         __SBI_HART_EXT_DATA(sscsrind, SBI_HART_EXT_SSCSRIND),
>         __SBI_HART_EXT_DATA(ssccfg, SBI_HART_EXT_SSCCFG),
> +       __SBI_HART_EXT_DATA(smrnmi, SBI_HART_EXT_SMRNMI),
>  };
>
>  _Static_assert(SBI_HART_EXT_MAX == array_size(sbi_hart_ext),
> @@ -706,6 +707,20 @@ void sbi_hart_get_extensions_str(struct sbi_scratch *scratch,
>                 sbi_strncpy(extensions_str, "none", nestr);
>  }
>
> +static int hart_smrnmi_get_allowed(void)
> +{
> +       unsigned long val;
> +       struct sbi_trap_info trap = {0};
> +
> +       val = csr_read_allowed(CSR_MNSTATUS, (unsigned long)&trap);
> +       if (!trap.cause) {
> +               val |= MNSTATUS_NMIE;
> +               csr_write(CSR_MNSTATUS, val);
> +               return true;
> +       } else {
> +               return false;
> +       }
> +
>  static unsigned long hart_pmp_get_allowed_addr(void)
>  {
>         unsigned long val = 0;
> @@ -775,6 +790,13 @@ static int hart_detect_features(struct sbi_scratch *scratch)
>         hfeatures->mhpm_mask = 0;
>         hfeatures->priv_version = SBI_HART_PRIV_VER_UNKNOWN;
>
> +       /*
> +        * Detect Resumable Non-Maskable Interrupts
> +        * If it exists we must enable it before all traps.
> +        */
> +       if (hart_smrnmi_get_allowed())
> +               __sbi_hart_update_extension(hfeatures, SBI_HART_EXT_SMRNMI, true);
> +

No need to detect Smrnmi using trap. The ISA string parsing
is sufficient.

Also, enabling mnstatus.NMIE should be done in mstatus_init() only
when SBI_HART_EXT_SMRNMI is available.

>  #define __check_hpm_csr(__csr, __mask)                                           \
>         oldval = csr_read_allowed(__csr, (ulong)&trap);                   \
>         if (!trap.cause) {                                                \
> --
> 2.34.1
>
>
> --
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Regards,
Anup