linux-kernel - Re: [PATCH 1/5] ARM: berlin: add SMP support

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Message-ID: <20140603141913.710a1f7e@xhacker>
Date:	Tue, 3 Jun 2014 14:19:13 +0800
From:	Jisheng Zhang <jszhang@...vell.com>
To:	Antoine Ténart 
	<antoine.tenart@...e-electrons.com>
CC:	Andrew Lunn <andrew@...n.ch>,
	"sebastian.hesselbarth@...il.com" <sebastian.hesselbarth@...il.com>,
	"thomas.petazzoni@...e-electrons.com" 
	<thomas.petazzoni@...e-electrons.com>, Jimmy Xu <zmxu@...vell.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"alexandre.belloni@...e-electrons.com" 
	<alexandre.belloni@...e-electrons.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 1/5] ARM: berlin: add SMP support

Hi Andrew, Antoine, 

On Mon, 2 Jun 2014 03:27:50 -0700
Antoine Ténart <antoine.tenart@...e-electrons.com> wrote:

> On Mon, Jun 02, 2014 at 12:03:32PM +0200, Andrew Lunn wrote:
> > On Mon, Jun 02, 2014 at 12:00:48PM +0200, Antoine Ténart wrote:
> > > Hi Andrew,
> > > 
> > > On Mon, Jun 02, 2014 at 11:47:15AM +0200, Andrew Lunn wrote:
> > > > On Mon, Jun 02, 2014 at 11:21:02AM +0200, Antoine Ténart wrote:
> > > > > +
> > > > > +static inline void berlin_reset_cpu(unsigned int cpu)
> > > > > +{
> > > > > +	u32 val;
> > > > > +
> > > > > +	val = readl(cpu_ctrl + CPU_RESET);
> > > > > +	val |= BIT(cpu_logical_map(cpu));
> > > > > +	writel(val, cpu_ctrl + CPU_RESET);
> > > > > +}
> > > > 
> > > > Is this performing a reset on the CPU, or is it taking it out of
> > > > reset?
> > > > 
> > > > If you are going to implement CPU hotplug at some point, you are going
> > > > to want to be able to put the CPU into reset, i.e. power it off, and
> > > > take it out of reset, i.e. power it on and getting it running. So it
> > > > might help if we get these function names clear now.
> > > 
> > > It is performing a reset on the CPU. berlin_perform_reset_cpu() then?
> > 
> > What happens if the CPU is powered off? Will a reset power it on?  Or
> > are you assuming the boot loader has powered it on?
> 
> I actually don't have information about this. For now let's assume the
> boot loader has powered on the CPUs.
> 

We don't support independently power off cpu on BG2 and BG2Q in linux kernel.
So we can assume that bootloader has powered on the CPUs

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