linux-kernel - Re: [PATCH 1/2] RISC-V: Fix counter restart during overflow for RV32

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Date:   Thu, 12 May 2022 21:06:01 +0530
From:   Anup Patel <anup@...infault.org>
To:     Heiko Stübner <heiko@...ech.de>
Cc:     Atish Patra <atishp@...osinc.com>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org List" <linux-kernel@...r.kernel.org>,
        Albert Ou <aou@...s.berkeley.edu>,
        Atish Patra <atishp@...shpatra.org>,
        Damien Le Moal <damien.lemoal@....com>,
        DTML <devicetree@...r.kernel.org>,
        Jisheng Zhang <jszhang@...nel.org>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Rob Herring <robh+dt@...nel.org>
Subject: Re: [PATCH 1/2] RISC-V: Fix counter restart during overflow for RV32

On Thu, May 12, 2022 at 6:12 PM Heiko Stübner <heiko@...ech.de> wrote:
>
> Am Donnerstag, 12. Mai 2022, 06:44:12 CEST schrieb Anup Patel:
> > On Thu, May 12, 2022 at 1:41 AM Atish Patra <atishp@...osinc.com> wrote:
> > >
> > > Pass the upper half of the initial value of the counter correctly
> > > for RV32.
> > >
> > > Fixes: 4905ec2fb7e6 ("RISC-V: Add sscofpmf extension support")
> > >
> > > Signed-off-by: Atish Patra <atishp@...osinc.com>
> > > ---
> > >  drivers/perf/riscv_pmu_sbi.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/perf/riscv_pmu_sbi.c b/drivers/perf/riscv_pmu_sbi.c
> > > index a1317a483512..24cea59612be 100644
> > > --- a/drivers/perf/riscv_pmu_sbi.c
> > > +++ b/drivers/perf/riscv_pmu_sbi.c
> > > @@ -526,7 +526,7 @@ static inline void pmu_sbi_start_overflow_mask(struct riscv_pmu *pmu,
> > >                         max_period = riscv_pmu_ctr_get_width_mask(event);
> > >                         init_val = local64_read(&hwc->prev_count) & max_period;
> > >                         sbi_ecall(SBI_EXT_PMU, SBI_EXT_PMU_COUNTER_START, idx, 1,
> > > -                                 flag, init_val, 0, 0);
> > > +                                 flag, init_val, init_val >> 32, 0);
> >
> > This should be under "#if __riscv_xlen == 32".
>
> What's the difference between using CONFIG_32BIT
> and checking the __riscv_xlen flag value?

It's one and the same.

>
> CONFIG_32BIT seems to be a bit the more kernel'ish
> way to do this, but it looks like most SBI parts check the
> __riscv_xlen instead.

I agree with you. We should prefer "#ifdef CONFIG_32BIT"
in this case to match the kernel coding style.

Currently, OpenSBI does not have CONFIG_xyz defines so
over there we use "#if __riscv_xlen == 32".

Regards,
Anup

>
>
> In any case, looking at the opensbi-side of the call,
> this fix is abviously correct, so
>
> Reviewed-by: Heiko Stuebner <heiko@...ech.de>
>
>
>