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Date: Fri, 29 Aug 2014 12:22:42 +0100
From: Mark Rutland <mark.rutland@arm.com>
To: Huang Tao <huangtao@rock-chips.com>
Cc: Kever Yang <kever.yang@rock-chips.com>,
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Subject: Re: [RESEND PATCH] ARM: dts: make arch-timer always on in rk3288 soc
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On Fri, Aug 29, 2014 at 04:06:40AM +0100, Huang Tao wrote:
> Hi, Mark:

Hi,

> 在 2014年08月28日 23:11, Mark Rutland 写道:
> > To clarify: if there are low power states that the CPU can enter where
> > we lose state, then this patch isn't correct.
> Right now, the software of RK3288 SoC only support CPU hotplug
> (cpu_on/off) and power off all CPUs on suspend.

Sure, but that's a Linux implementation detail rather than a fixed
property of the hardware. Given those states exist, the "always-on"
property is not appropriate.

> We do not implement cpuidle to power off CPU. Do you think we should
> introduce a broadcast timer?

If one is present, yes. 

> On our early kernel, I never see any interrupt on a broadcast timer
> (yes, we implement it with a external timer).

That's fine; Linux doesn't need to use it just yet. However, when we
want to use low power states later, it will be necessary to enable
placing all CPUS into a low power state.

If your external timer is already supported by an existing driver, there
is no reason not to add it now.

> > A more general approach would be to enable the broadcast hrtimer for
> > arm, as has been done for arm64.
> Yes. I think it should be done by arm framework.

Patches welcome.

I also think it would make sense to enable this for arm.

Thanks,
Mark.