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

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Date:   Fri, 6 Jul 2018 20:26:31 +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 12:43:52PM +0100, Mark Rutland wrote:
> Please see the devicetree spec [1], section 2.3.4. Valid values are:
> 
> * "okay" // equivalent to no status property present
> * "disabled"
> * "fail"
> * "fail-sss"
Nice tip, thx.

> I'm a bit confused. You write (1 << cpu) into cv<29, 0>, to enable a
> particular CPU, so I assume that bit uniquely identifies a CPU,
Yes, you're right and cr<29, 0>'s bit uniquely identifies a cpu.

> and
> therefore the reg is some unique ID for the CPU.
static int csky_of_cpu(struct device_node *node)
{
	const char *status;

	if (of_property_read_string(node, "status", &status))
		status = "okay";

	if (strcmp(status, "disabled") == 0)
		goto error;

	return 1;
error:
	return 0;
}

void __init setup_smp(void)
{
	struct device_node *node = NULL;
	int i = 0;

	while ((node = of_find_node_by_type(node, "cpu"))) {
		if (!csky_of_cpu(node))
			continue;

		set_cpu_possible(i, true);
		set_cpu_present(i, true);

		i++;
	}
}
Hmm?

No <reg> in next version patch, it's no use.

> I see.
> 
> Is this SMP bringup mechanism architectual, or are you likely to need
> another mechanism to turn on CPUs on future chips?
It's the only SMP bringup mechanism architectual for C-SKY SMP. There is
no another way in future and SOC vendor couldn't change it.

> You probably want to use an enable-method property to describe this.
No, thx.

 Guo Ren