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

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Date:	Mon, 2 Jun 2014 12:00:48 +0200
From:	Antoine Ténart 
	<antoine.tenart@...e-electrons.com>
To:	Andrew Lunn <andrew@...n.ch>
Cc:	Antoine Ténart 
	<antoine.tenart@...e-electrons.com>,
	sebastian.hesselbarth@...il.com,
	thomas.petazzoni@...e-electrons.com, zmxu@...vell.com,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	alexandre.belloni@...e-electrons.com, jszhang@...vell.com,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 1/5] ARM: berlin: add SMP support

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?

> > +
> > +static void __init berlin_smp_prepare_cpus(unsigned int max_cpus)
> > +{
> > +	struct device_node *np;
> > +	void __iomem *scu_base;
> > +	void __iomem *vectors_base;
> > +
> > +	np = of_find_compatible_node(NULL, NULL, "arm,cortex-a9-scu");
> > +	scu_base = of_iomap(np, 0);
> > +	of_node_put(np);
> > +	if (!scu_base)
> > +		return;
> > +
> > +	np = of_find_compatible_node(NULL, NULL, "marvell,berlin-cpu-ctrl");
> > +	cpu_ctrl = of_iomap(np, 0);
> > +	of_node_put(np);
> > +	if (!cpu_ctrl)
> > +		goto unmap_scu;
> > +
> > +	vectors_base = ioremap(CONFIG_VECTORS_BASE, SZ_32K);
> > +	if (!vectors_base)
> > +		goto unmap_scu;
> > +
> > +	scu_enable(scu_base);
> > +	flush_cache_all();
> > +
> > +	/*
> > +	 * Write the first instruction the CPU will execute after being reseted
> > +	 * in the reset exception register.
> > +	 */
> > +	writel(boot_inst, vectors_base + RESET_VECT);
> > +
> > +	/*
> > +	 * Write the secondary startup address into the SW reset address
> > +	 * register. This is used by boot_inst.
> 
> Maybe it would be better to call this the reset address vector instead
> of address register. It is in the vector space after all.

I don't have a strong opinion on this. I can update the 'reset exception
register' as well then.

Antoine

-- 
Antoine Ténart, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com
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