linux-kernel - Re: [PATCH V2 16/19] csky: SMP support

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Message-ID: <20180706113200.GA27148@guoren>
Date:   Fri, 6 Jul 2018 19:32:01 +0800
From:   Guo Ren <ren_guo@...ky.com>
To:     Mark Rutland <mark.rutland@....com>
Cc:     linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
        tglx@...utronix.de, daniel.lezcano@...aro.org,
        jason@...edaemon.net, arnd@...db.de, c-sky_gcc_upstream@...ky.com,
        gnu-csky@...tor.com, thomas.petazzoni@...tlin.com,
        wbx@...ibc-ng.org, green.hu@...il.com
Subject: Re: [PATCH V2 16/19] csky: SMP support

On Fri, Jul 06, 2018 at 06:24:33AM +0100, Mark Rutland wrote:
> > +	if (cpu >= NR_CPUS)
> > +		goto error;
> > +
> > +	if (of_property_read_string(node, "status", &status))
> > +		status = "enable";
> > +
> > +	if (strcmp(status, "disable") == 0)
> > +		goto error;
> 
> Please use of_device_is_available(node); 
Ok.

> "enable" is not a sensible value for
> the status property, and "disable" (rather than "disabled") is simply unusual.
> 
> Neither "enable" nor "disable" are correct values for the status property.

	cpus {
		#address-cells = <1>;
		#size-cells = <0>;
		cpu@0 {
			device_type = "cpu";
			reg = <0>;
			status = "on";
		};

		cpu@1 {
			device_type = "cpu";
			reg = <1>;
			status = "off";
		};
	};

> What is the value in the reg property, exactly?
See above, I'll remove the reg property and it's no use.

> Is there a unique ID in
> hardware for each CPU in the system?
There is no unique ID in current CPU: ck860.

> 
> It would be good to document this, e.g. as arm does in
> Documentation/devicetree/bindings/arm/cpus.txt
Ok.

> > +
> > +	return cpu;
> > +error:
> > +	return -ENODEV;
> > +}
> > +
> > +void __init setup_smp(void)
> > +{
> > +	struct device_node *node = NULL;
> > +	int cpu;
> > +
> > +	while ((node = of_find_node_by_type(node, "cpu"))) {
> > +		cpu = csky_of_cpu(node);
> > +		if (cpu >= 0) {
> > +			set_cpu_possible(cpu, true);
> > +			set_cpu_present(cpu, true);
> > +		}
> > +	}
> > +}
> 
> What happens if/when the value in the reg property is larger than NR_CPUS?
Bug. I'll add NR_CPUS limit.

> > +int __cpu_up(unsigned int cpu, struct task_struct *tidle)
> > +{
> > +	unsigned int tmp;
> > +
> > +	secondary_stack = (unsigned int)tidle->stack + THREAD_SIZE;
> > +
> > +	secondary_hint = mfcr("cr31");
> > +
> > +	secondary_ccr  = mfcr("cr18");
> > +
> > +	pr_info("%s: CPU%u\n", __func__, cpu);
> > +
> > +	tmp = mfcr("cr<29, 0>");
> > +	tmp |= 1 << cpu;
> > +	mtcr("cr<29, 0>", tmp);
> > +
> > +	while (!cpu_online(cpu));
> > +
> > +	secondary_stack = 0;
> > +
> > +	return 0;
> > +}
> 
> I don't see a start address being setup here, so I assume that CPUs branch to a
> fixed address out-of-reset. Does that mean that the kernel has to be loaded at
> a particular physical address on a given platform?
No, not a fixed address. I put it arch/csky/kernel/traps.c:79-83
trap_init()
#ifdef CONFIG_SMP
	mtcr("cr<28, 0>", virt_to_phys(vec_base));

	VEC_INIT(VEC_RESET, (void *)virt_to_phys(_start_smp_secondary));
#endi

 Guo Ren