[PATCH 1/2] riscv: Add stimecmp save and restore

[Nick Hu]

Hi Anup,

On Thu, Aug 29, 2024 at 1:18 PM Anup Patel <apatel at ventanamicro.com> wrote:
>
> On Thu, Aug 29, 2024 at 9:09 AM Nick Hu <nick.hu at sifive.com> wrote:
> >
> > If the HW support the SSTC extension, we should save and restore the
> > stimecmp register while cpu non retention suspend.
> >
> > Signed-off-by: Nick Hu <nick.hu at sifive.com>
> > ---
> >  arch/riscv/include/asm/suspend.h |  4 ++++
> >  arch/riscv/kernel/suspend.c      | 13 +++++++++++++
> >  2 files changed, 17 insertions(+)
> >
> > diff --git a/arch/riscv/include/asm/suspend.h b/arch/riscv/include/asm/suspend.h
> > index 4ffb022b097f..ffaac2efabb5 100644
> > --- a/arch/riscv/include/asm/suspend.h
> > +++ b/arch/riscv/include/asm/suspend.h
> > @@ -16,6 +16,10 @@ struct suspend_context {
> >         unsigned long envcfg;
> >         unsigned long tvec;
> >         unsigned long ie;
> > +#if __riscv_xlen < 64
> > +       unsigned long stimecmph;
> > +#endif
> > +       unsigned long stimecmp;
> >  #ifdef CONFIG_MMU
> >         unsigned long satp;
> >  #endif
> > diff --git a/arch/riscv/kernel/suspend.c b/arch/riscv/kernel/suspend.c
> > index c8cec0cc5833..3afd86e1abf7 100644
> > --- a/arch/riscv/kernel/suspend.c
> > +++ b/arch/riscv/kernel/suspend.c
> > @@ -19,6 +19,12 @@ void suspend_save_csrs(struct suspend_context *context)
> >         context->tvec = csr_read(CSR_TVEC);
> >         context->ie = csr_read(CSR_IE);
> >
> > +       if (riscv_has_extension_unlikely(RISCV_ISA_EXT_SSTC)) {
> > +               context->stimecmp = csr_read(CSR_STIMECMP);
> > +#if __riscv_xlen < 64
> > +               context->stimecmph = csr_read(CSR_STIMECMPH);
> > +#endif
> > +       }
>
> The suspend save/restore is enabled for the NoMMU kernel as well
> (which runs in M-mode) so it is better to save/restore stimecmp CSR
> only for MMU enabled kernels (just like satp CSR).
>
Good point. Will update that in the next version.
Thanks for the feedback.

> >         /*
> >          * No need to save/restore IP CSR (i.e. MIP or SIP) because:
> >          *
> > @@ -42,6 +48,13 @@ void suspend_restore_csrs(struct suspend_context *context)
> >         csr_write(CSR_TVEC, context->tvec);
> >         csr_write(CSR_IE, context->ie);
> >
> > +       if (riscv_has_extension_unlikely(RISCV_ISA_EXT_SSTC)) {
> > +               csr_write(CSR_STIMECMP, context->stimecmp);
> > +#if __riscv_xlen < 64
> > +               csr_write(CSR_STIMECMPH, context->stimecmph);
> > +#endif
> > +       }
> > +
> >  #ifdef CONFIG_MMU
> >         csr_write(CSR_SATP, context->satp);
> >  #endif
> > --
> > 2.34.1
> >
> >
>
> Regards,
> Anup

Regards,
Nick