linux-kernel - Re: [RFC PATCH] clocksource/drivers/riscv: Get rid of clocksource_arch

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Message-ID: <CA+V-a8vLtmo7VjQfZAnvLvjBADF_Zk3TNM62VJQnyxSBwjVDnQ@mail.gmail.com>
Date:   Wed, 28 Dec 2022 23:44:08 +0000
From:   "Lad, Prabhakar" <prabhakar.csengg@...il.com>
To:     Samuel Holland <samuel@...lland.org>
Cc:     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>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Conor Dooley <conor.dooley@...rochip.com>,
        Heiko Stuebner <heiko@...ech.de>,
        linux-riscv@...ts.infradead.org, Anup Patel <anup@...infault.org>,
        linux-renesas-soc@...r.kernel.org, linux-kernel@...r.kernel.org,
        Biju Das <biju.das.jz@...renesas.com>,
        Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
Subject: Re: [RFC PATCH] clocksource/drivers/riscv: Get rid of
 clocksource_arch_init() callback

Hi Samuel,

Thank you for the review.

On Tue, Dec 27, 2022 at 11:17 PM Samuel Holland <samuel@...lland.org> wrote:
>
> On 12/11/22 15:58, Prabhakar wrote:
> > From: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
> >
> > Having a clocksource_arch_init() callback always sets vdso_clock_mode to
> > VDSO_CLOCKMODE_ARCHTIMER if GENERIC_GETTIMEOFDAY is enabled, this is
> > required for the riscv-timer.
> >
> > This works for platforms where just riscv-timer clocksource is present.
> > On platforms where other clock sources are available we want them to
> > register with vdso_clock_mode set to VDSO_CLOCKMODE_NONE.
> >
> > On the Renesas RZ/Five SoC OSTM block can be used as clocksource [0], to
> > avoid multiple clock sources being registered as VDSO_CLOCKMODE_ARCHTIMER
> > move setting of vdso_clock_mode in the riscv-timer driver instead of doing
> > this in clocksource_arch_init() callback as done similarly for ARM/64
> > architecture.
>
> This is definitely a good change to make, but shouldn't we still prefer
> the architectural CSR-based clocksource over an MMIO-based clocksource?
> It has double the number of bits, and reading it should have less
> overhead. So I think we also want to increase the rating of
> riscv_clocksource.
>
For which now you have already have a patch posted.

> D1 is in the same situation, as timer-sun4i.c registers a clocksource
> with a higher rating than riscv_clocksource. Without this patch,
> tools/testing/selftests/vDSO/vdso_test_correctness fails. With this
> patch, it passes, so:
>
> Tested-by: Samuel Holland <samuel@...lland.org>
>
> > [0] drivers/clocksource/renesas-ostm.c
> >
> > Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
> > ---
> >  arch/riscv/Kconfig                | 1 -
> >  arch/riscv/kernel/time.c          | 9 ---------
> >  drivers/clocksource/timer-riscv.c | 7 +++++++
> >  3 files changed, 7 insertions(+), 10 deletions(-)
> >
> > diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> > index 7ea12de636bd..b269e062c1b1 100644
> > --- a/arch/riscv/Kconfig
> > +++ b/arch/riscv/Kconfig
> > @@ -12,7 +12,6 @@ config 32BIT
> >
> >  config RISCV
> >       def_bool y
> > -     select ARCH_CLOCKSOURCE_INIT
> >       select ARCH_ENABLE_HUGEPAGE_MIGRATION if HUGETLB_PAGE && MIGRATION
> >       select ARCH_ENABLE_SPLIT_PMD_PTLOCK if PGTABLE_LEVELS > 2
> >       select ARCH_HAS_BINFMT_FLAT
> > diff --git a/arch/riscv/kernel/time.c b/arch/riscv/kernel/time.c
> > index 8217b0f67c6c..42bee305e997 100644
> > --- a/arch/riscv/kernel/time.c
> > +++ b/arch/riscv/kernel/time.c
> > @@ -30,12 +30,3 @@ void __init time_init(void)
> >       of_clk_init(NULL);
> >       timer_probe();
> >  }
> > -
> > -void clocksource_arch_init(struct clocksource *cs)
> > -{
> > -#ifdef CONFIG_GENERIC_GETTIMEOFDAY
> > -     cs->vdso_clock_mode = VDSO_CLOCKMODE_ARCHTIMER;
> > -#else
> > -     cs->vdso_clock_mode = VDSO_CLOCKMODE_NONE;
> > -#endif
> > -}
> > diff --git a/drivers/clocksource/timer-riscv.c b/drivers/clocksource/timer-riscv.c
> > index 969a552da8d2..7ec9668cd36d 100644
> > --- a/drivers/clocksource/timer-riscv.c
> > +++ b/drivers/clocksource/timer-riscv.c
> > @@ -29,6 +29,12 @@
> >
> >  static DEFINE_STATIC_KEY_FALSE(riscv_sstc_available);
> >
> > +#ifdef CONFIG_GENERIC_GETTIMEOFDAY
> > +static enum vdso_clock_mode vdso_default = VDSO_CLOCKMODE_ARCHTIMER;
> > +#else
> > +static enum vdso_clock_mode vdso_default = VDSO_CLOCKMODE_NONE;
> > +#endif /* CONFIG_GENERIC_GETTIMEOFDAY */
>
> We don't have any workarounds like arm_arch_timer, so we do not need
> this indirection through vdso_default. You can set .vdso_clock_mode
> directly in the declaration of riscv_clocksource.
>
Agreed, I'll do that in v2.

Cheers,
Prabhakar