Re: [PATCH v7 3/4] RISC-V: Prefer sstc extension if available

[Atish Patra <atishp@atishpatra.org>]

On Mon, Jul 25, 2022 at 10:49 PM Atish Patra <atishp@atishpatra.org> wrote:
>
> On Fri, Jul 22, 2022 at 9:50 AM Atish Patra <atishp@rivosinc.com> wrote:
> >
> > RISC-V ISA has sstc extension which allows updating the next clock event
> > via a CSR (stimecmp) instead of an SBI call. This should happen dynamically
> > if sstc extension is available. Otherwise, it will fallback to SBI call
> > to maintain backward compatibility.
> >
> > Reviewed-by: Anup Patel <anup@brainfault.org>
> > Signed-off-by: Atish Patra <atishp@rivosinc.com>
> > ---
> >  drivers/clocksource/timer-riscv.c | 25 ++++++++++++++++++++++++-
> >  1 file changed, 24 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/clocksource/timer-riscv.c b/drivers/clocksource/timer-riscv.c
> > index 593d5a957b69..05f6cf067289 100644
> > --- a/drivers/clocksource/timer-riscv.c
> > +++ b/drivers/clocksource/timer-riscv.c
> > @@ -7,6 +7,9 @@
> >   * either be read from the "time" and "timeh" CSRs, and can use the SBI to
> >   * setup events, or directly accessed using MMIO registers.
> >   */
> > +
> > +#define pr_fmt(fmt) "riscv-timer: " fmt
> > +
> >  #include <linux/clocksource.h>
> >  #include <linux/clockchips.h>
> >  #include <linux/cpu.h>
> > @@ -20,14 +23,28 @@
> >  #include <linux/of_irq.h>
> >  #include <clocksource/timer-riscv.h>
> >  #include <asm/smp.h>
> > +#include <asm/hwcap.h>
> >  #include <asm/sbi.h>
> >  #include <asm/timex.h>
> >
> > +static DEFINE_STATIC_KEY_FALSE(riscv_sstc_available);
> > +
> >  static int riscv_clock_next_event(unsigned long delta,
> >                 struct clock_event_device *ce)
> >  {
> > +       u64 next_tval = get_cycles64() + delta;
> > +
> >         csr_set(CSR_IE, IE_TIE);
> > -       sbi_set_timer(get_cycles64() + delta);
> > +       if (static_branch_likely(&riscv_sstc_available)) {
> > +#if defined(CONFIG_32BIT)
> > +               csr_write(CSR_STIMECMP, next_tval & 0xFFFFFFFF);
> > +               csr_write(CSR_STIMECMPH, next_tval >> 32);
> > +#else
> > +               csr_write(CSR_STIMECMP, next_tval);
> > +#endif
> > +       } else
> > +               sbi_set_timer(next_tval);
> > +
> >         return 0;
> >  }
> >
> > @@ -165,6 +182,12 @@ static int __init riscv_timer_init_dt(struct device_node *n)
> >         if (error)
> >                 pr_err("cpu hp setup state failed for RISCV timer [%d]\n",
> >                        error);
> > +
> > +       if (riscv_isa_extension_available(NULL, SSTC)) {
> > +               pr_info("Timer interrupt in S-mode is available via sstc extension\n");
> > +               static_branch_enable(&riscv_sstc_available);
> > +       }
> > +
> >         return error;
> >  }
> >
> > --
> > 2.25.1
> >
>
> Hi Stephen,
> Can you please review this whenever you get a chance ? We probably
> need an ACK at least :)
>

Ping ?

> --
> Regards,
> Atish



-- 
Regards,
Atish