ARM: aspeed: Enable SMP boot

This brings the secondary CPU into Linux. It depends on the setup
performed by ASPEED's u-boot.

Signed-off-by: Joel Stanley <[e-mail]>

arch/arm/Makefile

···
 machine-$(CONFIG_ARCH_ACTIONS)		+= actions
 machine-$(CONFIG_ARCH_ALPINE)		+= alpine
 machine-$(CONFIG_ARCH_ARTPEC)		+= artpec
+machine-$(CONFIG_ARCH_ASPEED)           += aspeed
 machine-$(CONFIG_ARCH_AT91)		+= at91
 machine-$(CONFIG_ARCH_AXXIA)		+= axxia
 machine-$(CONFIG_ARCH_BCM)		+= bcm

arch/arm/mach-aspeed/Makefile

···
+# SPDX-License-Identifier: GPL-2.0-or-later
+# Copyright (C) ASPEED Technology Inc.
+# Copyright IBM Corp.
+
+obj-$(CONFIG_SMP) += platsmp.o

arch/arm/mach-aspeed/platsmp.c

···
+// SPDX-License-Identifier: GPL-2.0-or-later
+// Copyright (C) ASPEED Technology Inc.
+// Copyright IBM Corp.
+
+#include <linux/of_address.h>
+#include <linux/io.h>
+#include <linux/of.h>
+#include <linux/smp.h>
+
+#define BOOT_ADDR	0x00
+#define BOOT_SIG	0x04
+
+static struct device_node *secboot_node;
+
+static int aspeed_g6_boot_secondary(unsigned int cpu, struct task_struct *idle)
+{
+	void __iomem *base;
+
+	base = of_iomap(secboot_node, 0);
+	if (!base) {
+		pr_err("could not map the secondary boot base!");
+		return -ENODEV;
+	}
+
+	writel_relaxed(0, base + BOOT_ADDR);
+	writel_relaxed(__pa_symbol(secondary_startup_arm), base + BOOT_ADDR);
+	writel_relaxed((0xABBAAB00 | (cpu & 0xff)), base + BOOT_SIG);
+
+	dsb_sev();
+
+	iounmap(base);
+
+	return 0;
+}
+
+static void __init aspeed_g6_smp_prepare_cpus(unsigned int max_cpus)
+{
+	void __iomem *base;
+
+	secboot_node = of_find_compatible_node(NULL, NULL, "aspeed,ast2600-smpmem");
+	if (!secboot_node) {
+		pr_err("secboot device node found!!\n");
+		return;
+	}
+
+	base = of_iomap(secboot_node, 0);
+	if (!base) {
+		pr_err("could not map the secondary boot base!");
+		return;
+	}
+	__raw_writel(0xBADABABA, base + BOOT_SIG);
+
+	iounmap(base);
+}
+
+static const struct smp_operations aspeed_smp_ops __initconst = {
+	.smp_prepare_cpus	= aspeed_g6_smp_prepare_cpus,
+	.smp_boot_secondary	= aspeed_g6_boot_secondary,
+};
+
+CPU_METHOD_OF_DECLARE(aspeed_smp, "aspeed,ast2600-smp", &aspeed_smp_ops);