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@xxxxxxxxxxxx>
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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