[PATCH 1/2] powerpc/time: Use clockevents_register_device(), fixing an issue with large decrementer

[PATCH 1/2] powerpc/time: Use clockevents_register_device(), fixing an issue with large decrementer

[Anton Blanchard]

We currently cap the decrementer clockevent at 4 seconds, even on systems
with large decrementer support. Fix this by converting the code to use
clockevents_register_device() which calculates the upper bound based on
the max_delta passed in.

Signed-off-by: Anton Blanchard <anton@ozlabs.org>
---
 arch/powerpc/kernel/time.c | 17 +++--------------
 1 file changed, 3 insertions(+), 14 deletions(-)

diff --git a/arch/powerpc/kernel/time.c b/arch/powerpc/kernel/time.c
index 70f145e02487..6a1f0a084ca3 100644
--- a/arch/powerpc/kernel/time.c
+++ b/arch/powerpc/kernel/time.c
@@ -984,10 +984,10 @@ static void register_decrementer_clockevent(int cpu)
 	*dec = decrementer_clockevent;
 	dec->cpumask = cpumask_of(cpu);
 
+	clockevents_config_and_register(dec, ppc_tb_freq, 2, decrementer_max);
+
 	printk_once(KERN_DEBUG "clockevent: %s mult[%x] shift[%d] cpu[%d]\n",
 		    dec->name, dec->mult, dec->shift, cpu);
-
-	clockevents_register_device(dec);
 }
 
 static void enable_large_decrementer(void)
@@ -1035,18 +1035,7 @@ static void __init set_decrementer_max(void)
 
 static void __init init_decrementer_clockevent(void)
 {
-	int cpu = smp_processor_id();
-
-	clockevents_calc_mult_shift(&decrementer_clockevent, ppc_tb_freq, 4);
-
-	decrementer_clockevent.max_delta_ns =
-		clockevent_delta2ns(decrementer_max, &decrementer_clockevent);
-	decrementer_clockevent.max_delta_ticks = decrementer_max;
-	decrementer_clockevent.min_delta_ns =
-		clockevent_delta2ns(2, &decrementer_clockevent);
-	decrementer_clockevent.min_delta_ticks = 2;
-
-	register_decrementer_clockevent(cpu);
+	register_decrementer_clockevent(smp_processor_id());
 }
 
 void secondary_cpu_time_init(void)
-- 
2.17.1

[PATCH 2/2] powerpc/time: Add set_state_oneshot_stopped decrementer callback

[Anton Blanchard]

If CONFIG_PPC_WATCHDOG is enabled we always cap the decrementer to
0x7fffffff:

       if (IS_ENABLED(CONFIG_PPC_WATCHDOG))
                set_dec(0x7fffffff);
        else
                set_dec(decrementer_max);

If there are no future events, we don't reprogram the decrementer
after this and we end up with 0x7fffffff even on a large decrementer
capable system.

As suggested by Nick, add a set_state_oneshot_stopped callback
so we program the decrementer with decrementer_max if there are
no future events.

Signed-off-by: Anton Blanchard <anton@ozlabs.org>
---
 arch/powerpc/kernel/time.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/powerpc/kernel/time.c b/arch/powerpc/kernel/time.c
index 6a1f0a084ca3..40868f3ee113 100644
--- a/arch/powerpc/kernel/time.c
+++ b/arch/powerpc/kernel/time.c
@@ -111,6 +111,7 @@ struct clock_event_device decrementer_clockevent = {
 	.rating			= 200,
 	.irq			= 0,
 	.set_next_event		= decrementer_set_next_event,
+	.set_state_oneshot_stopped = decrementer_shutdown,
 	.set_state_shutdown	= decrementer_shutdown,
 	.tick_resume		= decrementer_shutdown,
 	.features		= CLOCK_EVT_FEAT_ONESHOT |
-- 
2.17.1

Re: [1/2] powerpc/time: Use clockevents_register_device(), fixing an issue with large decrementer

[Michael Ellerman]

On Mon, 2018-10-01 at 23:01:04 UTC, Anton Blanchard wrote:
> We currently cap the decrementer clockevent at 4 seconds, even on systems
> with large decrementer support. Fix this by converting the code to use
> clockevents_register_device() which calculates the upper bound based on
> the max_delta passed in.
> 
> Signed-off-by: Anton Blanchard <anton@ozlabs.org>

Series applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/8b78fdb045de60a4eb35460092bbd3

cheers

Re: [PATCH 1/2] powerpc/time: Use clockevents_register_device(), fixing an issue with large decrementer

[Michael Ellerman]

Anton Blanchard <anton@ozlabs.org> writes:

> diff --git a/arch/powerpc/kernel/time.c b/arch/powerpc/kernel/time.c
> index 70f145e02487..6a1f0a084ca3 100644
> --- a/arch/powerpc/kernel/time.c
> +++ b/arch/powerpc/kernel/time.c
> @@ -1035,18 +1035,7 @@ static void __init set_decrementer_max(void)
>  
>  static void __init init_decrementer_clockevent(void)
>  {
> -	int cpu = smp_processor_id();
> -
> -	clockevents_calc_mult_shift(&decrementer_clockevent, ppc_tb_freq, 4);
> -
> -	decrementer_clockevent.max_delta_ns =
> -		clockevent_delta2ns(decrementer_max, &decrementer_clockevent);
> -	decrementer_clockevent.max_delta_ticks = decrementer_max;
> -	decrementer_clockevent.min_delta_ns =
> -		clockevent_delta2ns(2, &decrementer_clockevent);
> -	decrementer_clockevent.min_delta_ticks = 2;
> -
> -	register_decrementer_clockevent(cpu);
> +	register_decrementer_clockevent(smp_processor_id());
>  }

This broke KVM PR :)

Because we no longer set the mult/shift in decrementer_clockevent, which
is used in kvmppc_emulate_dec().

The patch below fixes it, though it'd be nice to come up with something
cleaner eventually.

cheers


diff --git a/arch/powerpc/kernel/time.c b/arch/powerpc/kernel/time.c
index 6a1f0a084ca3..d21b2b88c0a7 100644
--- a/arch/powerpc/kernel/time.c
+++ b/arch/powerpc/kernel/time.c
@@ -1036,6 +1036,9 @@ static void __init set_decrementer_max(void)
 static void __init init_decrementer_clockevent(void)
 {
 	register_decrementer_clockevent(smp_processor_id());
+
+	/* Set values for KVM, see kvm_emulate_dec() */
+	decrementer_clockevent = *dec;
 }
 
 void secondary_cpu_time_init(void)

[PATCH 1/2] powerpc/time: Use clockevents_register_device(), fixing an issue with large decrementer

[Anton Blanchard]

We currently cap the decrementer clockevent at 4 seconds, even on systems
with large decrementer support. Fix this by converting the code to use
clockevents_register_device() which calculates the upper bound based on
the max_delta passed in.

Signed-off-by: Anton Blanchard <anton@samba.org>
---
 arch/powerpc/kernel/time.c | 17 +++--------------
 1 file changed, 3 insertions(+), 14 deletions(-)

diff --git a/arch/powerpc/kernel/time.c b/arch/powerpc/kernel/time.c
index 70f145e02487..6a1f0a084ca3 100644
--- a/arch/powerpc/kernel/time.c
+++ b/arch/powerpc/kernel/time.c
@@ -984,10 +984,10 @@ static void register_decrementer_clockevent(int cpu)
 	*dec = decrementer_clockevent;
 	dec->cpumask = cpumask_of(cpu);
 
+	clockevents_config_and_register(dec, ppc_tb_freq, 2, decrementer_max);
+
 	printk_once(KERN_DEBUG "clockevent: %s mult[%x] shift[%d] cpu[%d]\n",
 		    dec->name, dec->mult, dec->shift, cpu);
-
-	clockevents_register_device(dec);
 }
 
 static void enable_large_decrementer(void)
@@ -1035,18 +1035,7 @@ static void __init set_decrementer_max(void)
 
 static void __init init_decrementer_clockevent(void)
 {
-	int cpu = smp_processor_id();
-
-	clockevents_calc_mult_shift(&decrementer_clockevent, ppc_tb_freq, 4);
-
-	decrementer_clockevent.max_delta_ns =
-		clockevent_delta2ns(decrementer_max, &decrementer_clockevent);
-	decrementer_clockevent.max_delta_ticks = decrementer_max;
-	decrementer_clockevent.min_delta_ns =
-		clockevent_delta2ns(2, &decrementer_clockevent);
-	decrementer_clockevent.min_delta_ticks = 2;
-
-	register_decrementer_clockevent(cpu);
+	register_decrementer_clockevent(smp_processor_id());
 }
 
 void secondary_cpu_time_init(void)
-- 
2.17.1