linux-kernel - Re: [PATCH 1/2] riscv: Add stimecmp save and restore

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Message-ID: <CAKddAkBks46LEdmFfkDuwoCc-kxcf1KpghiROuh-JeNorHrMRQ@mail.gmail.com>
Date: Fri, 30 Aug 2024 13:53:11 +0800
From: Nick Hu <nick.hu@...ive.com>
To: Andrew Jones <ajones@...tanamicro.com>
Cc: greentime.hu@...ive.com, zong.li@...ive.com, 
	"Rafael J. Wysocki" <rafael@...nel.org>, Pavel Machek <pavel@....cz>, 
	Paul Walmsley <paul.walmsley@...ive.com>, Palmer Dabbelt <palmer@...belt.com>, 
	Albert Ou <aou@...s.berkeley.edu>, Daniel Lezcano <daniel.lezcano@...aro.org>, 
	Thomas Gleixner <tglx@...utronix.de>, Conor Dooley <conor.dooley@...rochip.com>, 
	Samuel Holland <samuel.holland@...ive.com>, Sunil V L <sunilvl@...tanamicro.com>, 
	linux-pm@...r.kernel.org, linux-riscv@...ts.infradead.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] riscv: Add stimecmp save and restore

Hi Andrew

On Thu, Aug 29, 2024 at 3:59 PM Andrew Jones <ajones@...tanamicro.com> wrote:
>
> On Thu, Aug 29, 2024 at 11:38:59AM GMT, Nick Hu 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@...ive.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
>
> I'm not sure the reduction in struct size is worth the #ifdeffery. If we
> just always add stimecmph, then we can also change the #ifdef's below to
> if's, i.e. if (__riscv_xlen < 64), which should still remove the code from
> 64-bit builds.
>
> Or maybe we need something like
>
> #if __riscv_xlen < 64
> #define csrh_write(r, v) csr_write(r, v)
> #else
> #define csrh_write(r, v)
> #endif
>
> in asm/csr.h and then use it for all the *h csrs, but keep the #if in
> the struct.
>
> Thanks,
> drew
>
If no other comment, I'll choose the csrh_write() because it can save
some memory and update in the next version.
Thanks for the suggestion!

> > +     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
> > +     }
> >       /*
> >        * 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,
Nick