Messages in this thread | | | Date | Thu, 6 Nov 2014 10:14:49 -0800 | Subject | Re: [PATCH] clocksource: arch_timer: Mark ARMv8 system timer as 'always-on' | From | Anatol Pomozov <> |
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Hi
On Thu, Nov 6, 2014 at 10:09 AM, Marc Zyngier <marc.zyngier@arm.com> wrote: > Hi Anatol, > > On 2014-11-06 17:57, Anatol Pomozov wrote: >> >> Quoting ARMv8 Reference Manual section D6.1: >> "The system counter must be implemented in an always-on power domain." > > > Yes. And the key words here are "system counter". That's the global counter, > not the per-cpu view of that, and critically nor comparators. > > The timers (per-cpu counter+comparator) will happily go down with the CPU, > and won't be able to wake it up. Exactly like ARMv7, by the way. > >> There is no need to keep 'always-on' configurable on ARMv8. We ignore >> this dts property value and unconditionally set it to true. >> >> The issue was discovered while working on ARMv8 board with only one timer >> (arm arch timer). If 'always-on' is false then it disables high-resolution >> timer functionality. > > > Yup, and that's by design (see above). The *only* case where it is really > "always-on" is when a virtual machine is running (if the vcpu is running > then the physical CPU is, and so is the timer). > > If your system really never does any form of PM, then fine, just put the DT > property in. Removing it is, I'm sorry to say, a bit short sighted.
Thanks for the clarification Marc. I will look if it possible to get the other (always-on) timer back.
Ignore my patch.
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