[PATCH 4/5] lib: sbi: Ensure coldboot HART supports next privilege mode

[Anup Patel]

> -----Original Message-----
> From: Atish Patra <atishp at atishpatra.org>
> Sent: 11 September 2020 06:40
> To: Anup Patel <Anup.Patel at wdc.com>
> Cc: Atish Patra <Atish.Patra at wdc.com>; Alistair Francis
> <Alistair.Francis at wdc.com>; Anup Patel <anup at brainfault.org>; OpenSBI
> <opensbi at lists.infradead.org>
> Subject: Re: [PATCH 4/5] lib: sbi: Ensure coldboot HART supports next
> privilege mode
> 
> On Wed, Sep 9, 2020 at 7:51 AM Anup Patel <anup.patel at wdc.com> wrote:
> >
> > The coldboot HART jumps to the next booting stage at the end of
> > init_coldboot() so it is absolutely necessary for coldboot HART to
> > support the privilege mode expected by the next booting stage.
> >
> > We extend the coldboot HART selection in sbi_init() to ensure that the
> > selected coldboot HART always supports privilege mode specified in
> > scratch space (i.e. scratch->next_mode). This will further help us
> > allow E-core (without MMU) on SiFive Unleashed and PolarFire ICICLE
> > boards to proceed further and wait in HSM STOPPED state.
> >
> > Signed-off-by: Anup Patel <anup.patel at wdc.com>
> > ---
> >  lib/sbi/sbi_init.c | 29 ++++++++++++++++++++++++++++-
> >  1 file changed, 28 insertions(+), 1 deletion(-)
> >
> > diff --git a/lib/sbi/sbi_init.c b/lib/sbi/sbi_init.c index
> > e1a1d96..65d81ba 100644
> > --- a/lib/sbi/sbi_init.c
> > +++ b/lib/sbi/sbi_init.c
> > @@ -295,6 +295,7 @@ static atomic_t coldboot_lottery =
> ATOMIC_INITIALIZER(0);
> >   */
> >  void __noreturn sbi_init(struct sbi_scratch *scratch)  {
> > +       bool next_mode_supported        = FALSE;
> >         bool coldboot                   = FALSE;
> >         u32 hartid                      = current_hartid();
> >         const struct sbi_platform *plat = sbi_platform_ptr(scratch);
> > @@ -303,7 +304,33 @@ void __noreturn sbi_init(struct sbi_scratch
> *scratch)
> >             sbi_platform_hart_invalid(plat, hartid))
> >                 sbi_hart_hang();
> >
> > -       if (atomic_xchg(&coldboot_lottery, 1) == 0)
> > +       switch (scratch->next_mode) {
> > +       case PRV_M:
> > +               next_mode_supported = TRUE;
> > +               break;
> > +       case PRV_S:
> > +               if (misa_extension('S'))
> > +                       next_mode_supported = TRUE;
> > +               break;
> > +       case PRV_U:
> > +               if (misa_extension('U'))
> > +                       next_mode_supported = TRUE;
> > +               break;
> > +       default:
> > +               sbi_hart_hang();
> > +       }
> > +
> > +       /*
> > +        * Only the HART supporting privilege mode specified in the
> > +        * scratch->next_mode should be allowed to become the coldboot
> > +        * HART because the coldboot HART will be directly jumping to
> > +        * the next booting stage.
> > +        *
> > +        * We use a lottery mechanism to select coldboot HART among
> > +        * HARTs which satisfy above condition.
> > +        */
> > +
> > +       if (next_mode_supported && atomic_xchg(&coldboot_lottery, 1)
> > + == 0)
> >                 coldboot = TRUE;
> >
> >         if (coldboot)
> > --
> > 2.25.1
> >
> >
> > --
> > opensbi mailing list
> > opensbi at lists.infradead.org
> > http://lists.infradead.org/mailman/listinfo/opensbi
> 
> 
> Reviewed-by: Atish Patra <atish.patra at wdc.com>

Applied this patch to the riscv/opensbi repo

Regards,
Anup