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[PATCH] clocksource: arm_arch_timer: Don't assume clock runs in suspend

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  [PATCH] clocksource: arm_arch_timer: Don't assume clock runs in suspend Brian Norris <briannorris@chromium.org> - 2016-09-16 07:50 +0200
    Re: [PATCH] clocksource: arm_arch_timer: Don't assume clock runs in  suspend Marc Zyngier <marc.zyngier@arm.com> - 2016-09-16 10:10 +0200
      Re: [PATCH] clocksource: arm_arch_timer: Don't assume clock runs in  suspend Brian Norris <briannorris@chromium.org> - 2016-09-20 01:20 +0200
        Re: [PATCH] clocksource: arm_arch_timer: Don't assume clock runs in  suspend Marc Zyngier <marc.zyngier@arm.com> - 2016-09-20 09:50 +0200

#1484680 — [PATCH] clocksource: arm_arch_timer: Don't assume clock runs in suspend

Since commit 4fbcdc813fb9 ("clocksource: arm_arch_timer: Use clocksource
for suspend timekeeping"), this driver assumes that the ARM architected
timer keeps running in suspend. This is not the case for some ARM SoCs,
depending on the HW state used for system suspend. Let's not assume that
all SoCs support this, and instead only support this if the device tree
explicitly tells us it's "always on". In all other cases, just fall back
to the RTC. This should be relatively harmless.

It seems fair to key the system-suspend behavior off the same property
used for C3STOP, since if the timer doesn't keep context for CPU sleep,
it likely doesn't for system sleep either.

Signed-off-by: Brian Norris <briannorris@chromium.org>
---
 drivers/clocksource/arm_arch_timer.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
index 57700541f951..e28677a34f02 100644
--- a/drivers/clocksource/arm_arch_timer.c
+++ b/drivers/clocksource/arm_arch_timer.c
@@ -490,7 +490,7 @@ static struct clocksource clocksource_counter = {
 	.rating	= 400,
 	.read	= arch_counter_read,
 	.mask	= CLOCKSOURCE_MASK(56),
-	.flags	= CLOCK_SOURCE_IS_CONTINUOUS | CLOCK_SOURCE_SUSPEND_NONSTOP,
+	.flags	= CLOCK_SOURCE_IS_CONTINUOUS,
 };
 
 static struct cyclecounter cyclecounter = {
@@ -526,6 +526,8 @@ static void __init arch_counter_register(unsigned type)
 		clocksource_counter.name = "arch_mem_counter";
 	}
 
+	if (!arch_timer_c3stop)
+		clocksource_counter.flags |= CLOCK_SOURCE_SUSPEND_NONSTOP;
 	start_count = arch_timer_read_counter();
 	clocksource_register_hz(&clocksource_counter, arch_timer_rate);
 	cyclecounter.mult = clocksource_counter.mult;
-- 
2.8.1.340.g018a5d0.dirty

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#1484766 — Re: [PATCH] clocksource: arm_arch_timer: Don't assume clock runs in suspend

Hi Brian,

On 16/09/16 06:49, Brian Norris wrote:
> Since commit 4fbcdc813fb9 ("clocksource: arm_arch_timer: Use clocksource
> for suspend timekeeping"), this driver assumes that the ARM architected
> timer keeps running in suspend. This is not the case for some ARM SoCs,
> depending on the HW state used for system suspend. Let's not assume that
> all SoCs support this, and instead only support this if the device tree
> explicitly tells us it's "always on". In all other cases, just fall back
> to the RTC. This should be relatively harmless.

I'm afraid you're confusing two things:
- the counter, which *must* carry on counting no matter what, as
(quoting the ARM ARM) "The system counter must be implemented in an
always-on power domain"
- the timer, which is allowed to be powered off, and can be tagged with
the "always-on" property to indicate that it is guaranteed to stay up
(which in practice only exists in virtual machines and never on real HW).

If your counter does stop counting when suspended, then this is starting
to either feel like a HW bug, or someone is killing the clock that feeds
this counter when entering suspend.

If this is the former, then we need a separate quirk to indicate the
non-standard behaviour. If it is the latter, don't do it! ;-)

> 
> It seems fair to key the system-suspend behavior off the same property
> used for C3STOP, since if the timer doesn't keep context for CPU sleep,
> it likely doesn't for system sleep either.
> 
> Signed-off-by: Brian Norris <briannorris@chromium.org>
> ---
>  drivers/clocksource/arm_arch_timer.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
> index 57700541f951..e28677a34f02 100644
> --- a/drivers/clocksource/arm_arch_timer.c
> +++ b/drivers/clocksource/arm_arch_timer.c
> @@ -490,7 +490,7 @@ static struct clocksource clocksource_counter = {
>  	.rating	= 400,
>  	.read	= arch_counter_read,
>  	.mask	= CLOCKSOURCE_MASK(56),
> -	.flags	= CLOCK_SOURCE_IS_CONTINUOUS | CLOCK_SOURCE_SUSPEND_NONSTOP,
> +	.flags	= CLOCK_SOURCE_IS_CONTINUOUS,
>  };
>  
>  static struct cyclecounter cyclecounter = {
> @@ -526,6 +526,8 @@ static void __init arch_counter_register(unsigned type)
>  		clocksource_counter.name = "arch_mem_counter";
>  	}
>  
> +	if (!arch_timer_c3stop)
> +		clocksource_counter.flags |= CLOCK_SOURCE_SUSPEND_NONSTOP;
>  	start_count = arch_timer_read_counter();
>  	clocksource_register_hz(&clocksource_counter, arch_timer_rate);
>  	cyclecounter.mult = clocksource_counter.mult;
> 

Given the above, I don't think this patch is acceptable.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...

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#1486944 — Re: [PATCH] clocksource: arm_arch_timer: Don't assume clock runs in suspend

On Fri, Sep 16, 2016 at 09:06:55AM +0100, Marc Zyngier wrote:
> Hi Brian,

Hi Marc,

Thanks for the quick response.

> On 16/09/16 06:49, Brian Norris wrote:
> > Since commit 4fbcdc813fb9 ("clocksource: arm_arch_timer: Use clocksource
> > for suspend timekeeping"), this driver assumes that the ARM architected
> > timer keeps running in suspend. This is not the case for some ARM SoCs,
> > depending on the HW state used for system suspend. Let's not assume that
> > all SoCs support this, and instead only support this if the device tree
> > explicitly tells us it's "always on". In all other cases, just fall back
> > to the RTC. This should be relatively harmless.
> 
> I'm afraid you're confusing two things:
> - the counter, which *must* carry on counting no matter what, as
> (quoting the ARM ARM) "The system counter must be implemented in an
> always-on power domain"
> - the timer, which is allowed to be powered off, and can be tagged with
> the "always-on" property to indicate that it is guaranteed to stay up
> (which in practice only exists in virtual machines and never on real HW).

Indeed, sorry for that confusion, and thanks for the explanations.

> If your counter does stop counting when suspended, then this is starting
> to either feel like a HW bug, or someone is killing the clock that feeds
> this counter when entering suspend.
> 
> If this is the former, then we need a separate quirk to indicate the
> non-standard behaviour. If it is the latter, don't do it! ;-)

It's beginning to seem more like a HW quirk which yields nonstandard
behavior. AIUI, this SoC normally runs the counter off its 24 MHz clock,
but for low power modes, this "always-on" domain switches over to a 32
KHz alternative clock. Unfortunately, the counter doesn't actually tick
when run this way. I'm trying to confirm with the chip designers
(Rockchip, RK3399) about the nature of the quirk, but I think we'll need
a separate DT flag for this behavior.

Brian

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#1487123 — Re: [PATCH] clocksource: arm_arch_timer: Don't assume clock runs in suspend

On 20/09/16 00:14, Brian Norris wrote:
> On Fri, Sep 16, 2016 at 09:06:55AM +0100, Marc Zyngier wrote:
>> Hi Brian,
> 
> Hi Marc,
> 
> Thanks for the quick response.
> 
>> On 16/09/16 06:49, Brian Norris wrote:
>>> Since commit 4fbcdc813fb9 ("clocksource: arm_arch_timer: Use clocksource
>>> for suspend timekeeping"), this driver assumes that the ARM architected
>>> timer keeps running in suspend. This is not the case for some ARM SoCs,
>>> depending on the HW state used for system suspend. Let's not assume that
>>> all SoCs support this, and instead only support this if the device tree
>>> explicitly tells us it's "always on". In all other cases, just fall back
>>> to the RTC. This should be relatively harmless.
>>
>> I'm afraid you're confusing two things:
>> - the counter, which *must* carry on counting no matter what, as
>> (quoting the ARM ARM) "The system counter must be implemented in an
>> always-on power domain"
>> - the timer, which is allowed to be powered off, and can be tagged with
>> the "always-on" property to indicate that it is guaranteed to stay up
>> (which in practice only exists in virtual machines and never on real HW).
> 
> Indeed, sorry for that confusion, and thanks for the explanations.
> 
>> If your counter does stop counting when suspended, then this is starting
>> to either feel like a HW bug, or someone is killing the clock that feeds
>> this counter when entering suspend.
>>
>> If this is the former, then we need a separate quirk to indicate the
>> non-standard behaviour. If it is the latter, don't do it! ;-)
> 
> It's beginning to seem more like a HW quirk which yields nonstandard
> behavior. AIUI, this SoC normally runs the counter off its 24 MHz clock,
> but for low power modes, this "always-on" domain switches over to a 32
> KHz alternative clock. Unfortunately, the counter doesn't actually tick
> when run this way. I'm trying to confirm with the chip designers
> (Rockchip, RK3399) about the nature of the quirk, but I think we'll need
> a separate DT flag for this behavior.

The counter is allowed to be clocked at a different rate, as long as it
is incremented by the frequency ratio on each tick of the new frequency.
In your case, the counter should increment by 750 on each tick of the
32kHz clock. If the rk3399 implementation doesn't do this, then this is
a bug, and we need a quirk to work around it.

Note that such a quirk will have some other impacts, such as the
gettimeofday implementation in the VDSO (which relies on the counter
making forward progress). There could be other issues in the timer
subsystem as well... This doesn't look like a pleasant thing to fix.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...

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