On Tue, Jul 19, 2022 at 12:12 PM Samuel Holland <samuel@xxxxxxxxxxxx> wrote:
>
> Hi Anup,
>
> On 7/19/22 12:47 AM, Anup Patel wrote:
> > We should set CLOCK_EVT_FEAT_C3STOP for a clock_event_device only when
> > riscv,timer-always-on DT property is not present for the corresponding
> > CPU.
>
> The timer maintaining its context (and continuing to count) during non-retentive
> CPU suspend is not sufficient to drop CLOCK_EVT_FEAT_C3STOP.
>
> Another requirement is that the timer interrupt is generated and routed outside
> the CPU's power/reset domain, to whatever hardware is responsible for turning
> the CPU back on. It does not matter if the timer interrupt fires, if that
> interrupt cannot wake up the CPU.
>
> So something closer to "riscv,timer-can-wake-cpu" would be a more accurate
> property name for how you are using it.
I agree with your suggestion. Let's make this DT property name aligned with
what it is doing.
>
> And even then, that ability is a property of the SBI implementation, not just
> the hardware. In the motivating example for the flag (Allwinner D1), the CLINT
> cannot wake the CPU from reset, but the SoC contains other MMIO timers that can.
> So the capability of the SBI timer extension depends on which timer hardware the
> SBI implementation chooses to use. So I am not sure that the property belongs in
> the CPU node.
>
> Maybe it makes sense to report this capability via a function in the SBI timer
> extension?
Well, the timer interrupt not firing in non-retentive suspend is an attribute of
underlying platform and not of the SBI implementation (firmware/hypervisor)
hence should be described in DT or ACPI.
Also, the timer interrupt not firing in non-retentive suspend is also possible
with RISC-V Sstc extension (i.e stimecmp CSRs) so the proposed DT
property will be useful for platforms with Sstc extension as well.
Regards,
Anup
>
> Regards,
> Samuel
>
> > This way CLOCK_EVT_FEAT_C3STOP feature is set for clock_event_device
> > based on RISC-V platform capabilities rather than having it set for
> > all RISC-V platforms.
> >
> > Signed-off-by: Anup Patel <apatel@xxxxxxxxxxxxxxxx>
> > ---
> > drivers/clocksource/timer-riscv.c | 6 +++++-
> > 1 file changed, 5 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/clocksource/timer-riscv.c b/drivers/clocksource/timer-riscv.c
> > index 593d5a957b69..3015324f2b59 100644
> > --- a/drivers/clocksource/timer-riscv.c
> > +++ b/drivers/clocksource/timer-riscv.c
> > @@ -34,7 +34,7 @@ static int riscv_clock_next_event(unsigned long delta,
> > static unsigned int riscv_clock_event_irq;
> > static DEFINE_PER_CPU(struct clock_event_device, riscv_clock_event) = {
> > .name = "riscv_timer_clockevent",
> > - .features = CLOCK_EVT_FEAT_ONESHOT | CLOCK_EVT_FEAT_C3STOP,
> > + .features = CLOCK_EVT_FEAT_ONESHOT,
> > .rating = 100,
> > .set_next_event = riscv_clock_next_event,
> > };
> > @@ -65,9 +65,13 @@ static struct clocksource riscv_clocksource = {
> > static int riscv_timer_starting_cpu(unsigned int cpu)
> > {
> > struct clock_event_device *ce = per_cpu_ptr(&riscv_clock_event, cpu);
> > + struct device_node *np = of_get_cpu_node(cpu, NULL);
> >
> > ce->cpumask = cpumask_of(cpu);
> > ce->irq = riscv_clock_event_irq;
> > + if (!of_property_read_bool(np, "riscv,timer-always-on"))
> > + ce->features |= CLOCK_EVT_FEAT_C3STOP;
> > + of_node_put(np);
> > clockevents_config_and_register(ce, riscv_timebase, 100, 0x7fffffff);
> >
> > enable_percpu_irq(riscv_clock_event_irq,
> >
>
