Messages in this thread | | | Subject | Re: [PATCH 2/2] arm64: dts: mt8173: add timer node | From | Sudeep Holla <> | Date | Thu, 17 Sep 2015 17:13:16 +0100 |
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On 17/09/15 15:56, Yingjoe Chen wrote: > On Thu, 2015-09-17 at 14:51 +0100, Sudeep Holla wrote: >> >> On 16/09/15 03:04, Yingjoe Chen wrote: >>> From: Daniel Kurtz <djkurtz@chromium.org> >>> >>> Add device node to enable GPT timer. This timer will be >>> used as sched clock source. >>> >> >> Interesting any known issues with or advantage over the arch timers >> to prefer it as sched clock source. I see even arch timers are present >> in DT, hence the question. Or is it just a incorrect commit log ? >> >> How does this get selected as sched clock source ? I don't see >> sched_clock_register in mtk_timer.c >> >> To be clear, I am not against adding this timer support, but just want >> to know is it preferred for sched clock source ? if yes why ? better >> resolution ? > > Hi Sudeep, > > Thanks for your review. > > I hit the send too soon and missed cover letter, please see: > http://lists.infradead.org/pipermail/linux-mediatek/2015-September/002303.html >
OK
> The main reason to use GPT as sched clock is it won't stop during idle. > >
I think your are confusing the system counter with arch timers. System counter is always-on, but the arch timers(logic implementing timers comparators) might not be off when the processor is powered down.
I think you need this timer and are using it for low power idle states in which case you will use this as a clock event and not clock source. It will be used as a hardware broadcast event source.
There's no call to sched_clock_register in mtk_timer.c, so it can't be the sched clock, so you need to fix the commit log.
[...]
>>> diff --git a/arch/arm64/boot/dts/mediatek/mt8173.dtsi b/arch/arm64/boot/dts/mediatek/mt8173.dtsi >>> index d18ee42..d763803 100644 >>> --- a/arch/arm64/boot/dts/mediatek/mt8173.dtsi >>> +++ b/arch/arm64/boot/dts/mediatek/mt8173.dtsi >>> @@ -238,6 +238,15 @@ >>> reg = <0 0x10007000 0 0x100>; >>> }; >>> >>> + timer: timer@10008000 { >>> + compatible = "mediatek,mt8173-timer", >> >> Missing documentation ? I am referring upstream and it might be in some >> patches already queued perhaps ? > > This is documented in > Documentation/devicetree/bindings/timer/mediatek,mtk-timer.txt. > Do you mean I should add "mediatek,mt8173-timer" to that file? >
Yes
Regards, Sudeep
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