linux-kernel - Re: [RESEND PATCH] ARM: dts: make arch-timer always on in rk3288 soc

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Date:	Thu, 28 Aug 2014 16:11:21 +0100
From:	Mark Rutland <mark.rutland@....com>
To:	Kever Yang <kever.yang@...k-chips.com>
Cc:	"heiko@...ech.de" <heiko@...ech.de>,
	"dianders@...omium.org" <dianders@...omium.org>,
	"sonnyrao@...omium.org" <sonnyrao@...omium.org>,
	"addy.ke@...k-chips.com" <addy.ke@...k-chips.com>,
	"cf@...k-chips.com" <cf@...k-chips.com>,
	"xjq@...k-chips.com" <xjq@...k-chips.com>,
	"wulf@...k-chips.com" <wulf@...k-chips.com>,
	"lyz@...k-chips.com" <lyz@...k-chips.com>,
	"hj@...k-chips.com" <hj@...k-chips.com>,
	"huangtao@...k-chips.com" <huangtao@...k-chips.com>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <Pawel.Moll@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Russell King <linux@....linux.org.uk>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	lorenzo.pieralisi@....com
Subject: Re: [RESEND PATCH] ARM: dts: make arch-timer always on in rk3288 soc

On Thu, Aug 28, 2014 at 10:17:58AM +0100, Mark Rutland wrote:
> Hi Kever,
> 
> On Thu, Aug 28, 2014 at 02:40:17AM +0100, Kever Yang wrote:
> > We need use the hrtimer, which need the arch-timer to be 'always-on'
> 
> I asked a question on the last posting [1]. Can you please confirm
> either way?
> 
> Thanks,
> Mark.
> 
> [1] lists.infradead.org/pipermail/linux-arm-kernel/2014-August/282327.html

To clarify: if there are low power states that the CPU can enter where
we lose state, then this patch isn't correct.

A more general approach would be to enable the broadcast hrtimer for
arm, as has been done for arm64.

See commit 5d1638acb9f6 (tick: Introduce hrtimer based broadcast) which
introduced the broadcast hrtimer, and commit 9358d755bd5c (arm64:
kernel: initialize broadcast hrtimer based clock event device) which
added the requisite plumbing for arm64.

Mark.

> 
> > Signed-off-by: Kever Yang <kever.yang@...k-chips.com>
> > ---
> > 
> >  arch/arm/boot/dts/rk3288.dtsi | 1 +
> >  1 file changed, 1 insertion(+)
> > 
> > diff --git a/arch/arm/boot/dts/rk3288.dtsi b/arch/arm/boot/dts/rk3288.dtsi
> > index 5950b0a..698e6ea 100644
> > --- a/arch/arm/boot/dts/rk3288.dtsi
> > +++ b/arch/arm/boot/dts/rk3288.dtsi
> > @@ -76,6 +76,7 @@
> >  			     <GIC_PPI 11 (GIC_CPU_MASK_SIMPLE(4) | IRQ_TYPE_LEVEL_HIGH)>,
> >  			     <GIC_PPI 10 (GIC_CPU_MASK_SIMPLE(4) | IRQ_TYPE_LEVEL_HIGH)>;
> >  		clock-frequency = <24000000>;
> > +		always-on;
> >  	};
> >  
> >  	i2c1: i2c@...40000 {
> > -- 
> > 1.9.1
> > 
> > --
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