[RFC PATCH 01/12] lib: sbi_hart: detect RISC-V Worlds ISA extensions
Yu-Chien Peter Lin
peter.lin at sifive.com
Sun Jul 19 20:14:46 PDT 2026
Hi Oza,
On Mon, Jul 13, 2026 at 01:58:42PM -0700, Pawandeep Oza wrote:
> On Fri, Jun 26, 2026 at 3:16 AM Yu-Chien Peter Lin <peter.lin at sifive.com> wrote:
> >
> > Add detection for RISC-V Worlds ISA extensions (Smwid, Smlwid,
> > Smlwidlist, Smwiddeleg, Sswid) via ISA string detection and
> > CSR probes.
> >
> > These feature flags enable subsequent patches to conditionally
> > configure World ID CSRs and print boot-time Worlds status.
> >
> > Signed-off-by: Yu-Chien Peter Lin <peter.lin at sifive.com>
> > ---
> > include/sbi/riscv_encoding.h | 12 +++++++++
> > include/sbi/sbi_hart.h | 10 +++++++
> > lib/sbi/sbi_hart.c | 51 ++++++++++++++++++++++++++++++++++++
> > 3 files changed, 73 insertions(+)
> >
> > diff --git a/include/sbi/riscv_encoding.h b/include/sbi/riscv_encoding.h
> > index ffe7666c..271820fd 100644
> > --- a/include/sbi/riscv_encoding.h
> > +++ b/include/sbi/riscv_encoding.h
> > @@ -400,6 +400,9 @@
> > /* Supervisor Resource Management Configuration CSRs */
> > #define CSR_SRMCFG 0x181
> >
> > +/* Supervisor World-ID CSR (Sswid) */
> > +#define CSR_SLWID 0x190
> Oza: Misleading comment -
> should be
> Supervisor WID value for lower privilege modes Register
Okay, will improve wording.
> > +
> > /* Machine-Level Control transfer records CSRs */
> > #define CSR_MCTRCTL 0x34e
> >
> > @@ -520,6 +523,15 @@
> > #define CSR_MTINST 0x34a
> > #define CSR_MTVAL2 0x34b
> >
> > +/* Machine World-ID CSRs (Smwid, Smlwid, Smlwidlist, Smwiddeleg) */
> > +#define CSR_MLWID 0x390
> > +#define CSR_MWID 0x391
> > +#define CSR_MWIDDELEG 0x748
> > +#define CSR_MLWIDLIST 0x749
> > +
> > +/* mwid lock bit */
> > +#define MWID_LOCK (_UL(1) << (__riscv_xlen - 1))
> > +
> > /* Machine Memory Protection */
> > #define CSR_PMPCFG0 0x3a0
> > #define CSR_PMPCFG1 0x3a1
> > diff --git a/include/sbi/sbi_hart.h b/include/sbi/sbi_hart.h
> > index 543393bb..2941809e 100644
> > --- a/include/sbi/sbi_hart.h
> > +++ b/include/sbi/sbi_hart.h
> > @@ -95,6 +95,16 @@ enum sbi_hart_extensions {
> > SBI_HART_EXT_F,
> > /** Hart has D extension */
> > SBI_HART_EXT_D,
> > + /** Hart has Smwid extension */
> > + SBI_HART_EXT_SMWID,
> > + /** Hart has Smlwid extension */
> > + SBI_HART_EXT_SMLWID,
> > + /** Hart has Smlwidlist extension */
> > + SBI_HART_EXT_SMLWIDLIST,
> > + /** Hart has Smwiddeleg extension */
> > + SBI_HART_EXT_SMWIDDELEG,
> > + /** Hart has Sswid extension */
> > + SBI_HART_EXT_SSWID,
> >
> > /** Maximum index of Hart extension */
> > SBI_HART_EXT_MAX,
> > diff --git a/lib/sbi/sbi_hart.c b/lib/sbi/sbi_hart.c
> > index 21713816..0c584bfc 100644
> > --- a/lib/sbi/sbi_hart.c
> > +++ b/lib/sbi/sbi_hart.c
> > @@ -402,6 +402,11 @@ const struct sbi_hart_ext_data sbi_hart_ext[] = {
> > __SBI_HART_EXT_DATA(v, SBI_HART_EXT_V),
> > __SBI_HART_EXT_DATA(f, SBI_HART_EXT_F),
> > __SBI_HART_EXT_DATA(d, SBI_HART_EXT_D),
> > + __SBI_HART_EXT_DATA(smwid, SBI_HART_EXT_SMWID),
> > + __SBI_HART_EXT_DATA(smlwid, SBI_HART_EXT_SMLWID),
> > + __SBI_HART_EXT_DATA(smlwidlist, SBI_HART_EXT_SMLWIDLIST),
> > + __SBI_HART_EXT_DATA(smwiddeleg, SBI_HART_EXT_SMWIDDELEG),
> > + __SBI_HART_EXT_DATA(sswid, SBI_HART_EXT_SSWID),
> > };
> >
> > _Static_assert(SBI_HART_EXT_MAX == array_size(sbi_hart_ext),
> > @@ -689,6 +694,52 @@ __pmp_skip:
> > /* Detect if hart support sdtrig (debug triggers) */
> > __check_ext_csr(SBI_HART_PRIV_VER_UNKNOWN,
> > CSR_TSELECT, SBI_HART_EXT_SDTRIG);
> > + /* Detect if hart supports Smwid (mwid CSR) */
> > + __check_ext_csr(SBI_HART_PRIV_VER_UNKNOWN,
> > + CSR_MWID, SBI_HART_EXT_SMWID);
> > + /* Detect if hart supports Smlwid (mlwid CSR) */
> > + __check_ext_csr(SBI_HART_PRIV_VER_UNKNOWN,
> > + CSR_MLWID, SBI_HART_EXT_SMLWID);
> > + /* Detect if hart supports Smlwidlist (mlwidlist CSR). */
> > + __check_ext_csr(SBI_HART_PRIV_VER_UNKNOWN,
> > + CSR_MLWIDLIST, SBI_HART_EXT_SMLWIDLIST);
> > + /*
> > + * Detect if hart supports Smwiddeleg & Sswid.
> > + * Smwiddeleg requires Smlwid. Sswid requires Smwiddeleg.
> > + */
> > + if (sbi_hart_has_extension(scratch, SBI_HART_EXT_SMLWID)) {
> > + unsigned long old_mwiddeleg, new_mwiddeleg;
> > +
> > + old_mwiddeleg = csr_read_allowed(CSR_MWIDDELEG, &trap);
> Oza: why not use __check_ext_csr at all the following ?
Yes, __check_ext_csr(CSR_MWIDDELEG, SBI_HART_EXT_SMWIDDELEG) is
sufficient Smwiddeleg which also implies Sswid.
Will update the ISA detection here.
Thanks,
Peter Lin
> > + if (trap.cause)
> > + goto skip_smwiddeleg;
> > +
> > + csr_write_allowed(CSR_MWIDDELEG, &trap, ~0UL);
> > + if (trap.cause)
> > + goto skip_smwiddeleg;
> > +
> > + new_mwiddeleg = csr_read_allowed(CSR_MWIDDELEG, &trap);
> > + if (trap.cause) {
> > + csr_write(CSR_MWIDDELEG, old_mwiddeleg);
> > + goto skip_smwiddeleg;
> > + }
> > +
> > + if (new_mwiddeleg) {
> > + __sbi_hart_update_extension(hfeatures,
> > + SBI_HART_EXT_SMWIDDELEG, true);
> > +
> > + csr_read_allowed(CSR_SLWID, &trap);
> > + if (!trap.cause) {
> > + __sbi_hart_update_extension(hfeatures,
> > + SBI_HART_EXT_SSWID, true);
> > + }
> > + }
> > +
> > + csr_write(CSR_MWIDDELEG, old_mwiddeleg);
> > +
> > +skip_smwiddeleg:
> > + ;
> > + }
> >
> > #undef __check_ext_csr
> >
> > --
> > 2.43.7
> >
> >
> > --
> > opensbi mailing list
> > opensbi at lists.infradead.org
> > http://lists.infradead.org/mailman/listinfo/opensbi
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