ARM: add SMP support for Broadcom mobile SoCs

This patch adds SMP support for BCM281XX and BCM21664 family SoCs.

This feature is controlled with a distinct config option such that
an SMP-enabled multi-v7 binary can be configured to run these SoCs
in uniprocessor mode.  Since this SMP functionality is used for
multiple Broadcom mobile chip families the config option is called
ARCH_BCM_MOBILE_SMP (for lack of a better name).

On SoCs of this type, the secondary core is not held in reset on
power-on.  Instead it loops in a ROM-based holding pen.  To release
it, one must write into a special register a jump address whose
low-order bits have been replaced with a secondary core's id, then
trigger an event with SEV.  On receipt of an event, the ROM code
will examine the register's contents, and if the low-order bits
match its cpu id, it will clear them and write the value back to the
register just prior to jumping to the address specified.

The location of the special register is defined in the device tree
using a "secondary-boot-reg" property in a node whose "enable-method"
matches.

Derived from code originally provided by Ray Jui <rjui@broadcom.com>

Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: Matt Porter <mporter@linaro.org>

1 files changed, 202 insertions, 0 deletions

diff --git a/arch/arm/mach-bcm/kona_smp.c b/arch/arm/mach-bcm/kona_smp.c
new file mode 100644
index 000000000000..66a0465528a5
--- /dev/null
+++ b/arch/arm/mach-bcm/kona_smp.c
@@ -0,0 +1,202 @@
+/*
+ * Copyright (C) 2014 Broadcom Corporation
+ * Copyright 2014 Linaro Limited
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation version 2.
+ *
+ * This program is distributed "as is" WITHOUT ANY WARRANTY of any
+ * kind, whether express or implied; without even the implied warranty
+ * of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+
+#include <linux/init.h>
+#include <linux/errno.h>
+#include <linux/io.h>
+#include <linux/of.h>
+#include <linux/sched.h>
+
+#include <asm/smp.h>
+#include <asm/smp_plat.h>
+#include <asm/smp_scu.h>
+
+/* Size of mapped Cortex A9 SCU address space */
+#define CORTEX_A9_SCU_SIZE	0x58
+
+#define SECONDARY_TIMEOUT_NS	NSEC_PER_MSEC	/* 1 msec (in nanoseconds) */
+#define BOOT_ADDR_CPUID_MASK	0x3
+
+/* Name of device node property defining secondary boot register location */
+#define OF_SECONDARY_BOOT	"secondary-boot-reg"
+
+/* I/O address of register used to coordinate secondary core startup */
+static u32	secondary_boot;
+
+/*
+ * Enable the Cortex A9 Snoop Control Unit
+ *
+ * By the time this is called we already know there are multiple
+ * cores present.  We assume we're running on a Cortex A9 processor,
+ * so any trouble getting the base address register or getting the
+ * SCU base is a problem.
+ *
+ * Return 0 if successful or an error code otherwise.
+ */
+static int __init scu_a9_enable(void)
+{
+	unsigned long config_base;
+	void __iomem *scu_base;
+
+	if (!scu_a9_has_base()) {
+		pr_err("no configuration base address register!\n");
+		return -ENXIO;
+	}
+
+	/* Config base address register value is zero for uniprocessor */
+	config_base = scu_a9_get_base();
+	if (!config_base) {
+		pr_err("hardware reports only one core\n");
+		return -ENOENT;
+	}
+
+	scu_base = ioremap((phys_addr_t)config_base, CORTEX_A9_SCU_SIZE);
+	if (!scu_base) {
+		pr_err("failed to remap config base (%lu/%u) for SCU\n",
+			config_base, CORTEX_A9_SCU_SIZE);
+		return -ENOMEM;
+	}
+
+	scu_enable(scu_base);
+
+	iounmap(scu_base);	/* That's the last we'll need of this */
+
+	return 0;
+}
+
+static void __init bcm_smp_prepare_cpus(unsigned int max_cpus)
+{
+	static cpumask_t only_cpu_0 = { CPU_BITS_CPU0 };
+	struct device_node *node;
+	int ret;
+
+	BUG_ON(secondary_boot);		/* We're called only once */
+
+	/*
+	 * This function is only called via smp_ops->smp_prepare_cpu().
+	 * That only happens if a "/cpus" device tree node exists
+	 * and has an "enable-method" property that selects the SMP
+	 * operations defined herein.
+	 */
+	node = of_find_node_by_path("/cpus");
+	BUG_ON(!node);
+
+	/*
+	 * Our secondary enable method requires a "secondary-boot-reg"
+	 * property to specify a register address used to request the
+	 * ROM code boot a secondary code.  If we have any trouble
+	 * getting this we fall back to uniprocessor mode.
+	 */
+	if (of_property_read_u32(node, OF_SECONDARY_BOOT, &secondary_boot)) {
+		pr_err("%s: missing/invalid " OF_SECONDARY_BOOT " property\n",
+			node->name);
+		ret = -ENOENT;		/* Arrange to disable SMP */
+		goto out;
+	}
+
+	/*
+	 * Enable the SCU on Cortex A9 based SoCs.  If -ENOENT is
+	 * returned, the SoC reported a uniprocessor configuration.
+	 * We bail on any other error.
+	 */
+	ret = scu_a9_enable();
+out:
+	of_node_put(node);
+	if (ret) {
+		/* Update the CPU present map to reflect uniprocessor mode */
+		BUG_ON(ret != -ENOENT);
+		pr_warn("disabling SMP\n");
+		init_cpu_present(&only_cpu_0);
+	}
+}
+
+/*
+ * The ROM code has the secondary cores looping, waiting for an event.
+ * When an event occurs each core examines the bottom two bits of the
+ * secondary boot register.  When a core finds those bits contain its
+ * own core id, it performs initialization, including computing its boot
+ * address by clearing the boot register value's bottom two bits.  The
+ * core signals that it is beginning its execution by writing its boot
+ * address back to the secondary boot register, and finally jumps to
+ * that address.
+ *
+ * So to start a core executing we need to:
+ * - Encode the (hardware) CPU id with the bottom bits of the secondary
+ *   start address.
+ * - Write that value into the secondary boot register.
+ * - Generate an event to wake up the secondary CPU(s).
+ * - Wait for the secondary boot register to be re-written, which
+ *   indicates the secondary core has started.
+ */
+static int bcm_boot_secondary(unsigned int cpu, struct task_struct *idle)
+{
+	void __iomem *boot_reg;
+	phys_addr_t boot_func;
+	u64 start_clock;
+	u32 cpu_id;
+	u32 boot_val;
+	bool timeout = false;
+
+	cpu_id = cpu_logical_map(cpu);
+	if (cpu_id & ~BOOT_ADDR_CPUID_MASK) {
+		pr_err("bad cpu id (%u > %u)\n", cpu_id, BOOT_ADDR_CPUID_MASK);
+		return -EINVAL;
+	}
+
+	if (!secondary_boot) {
+		pr_err("required secondary boot register not specified\n");
+		return -EINVAL;
+	}
+
+	boot_reg = ioremap_nocache((phys_addr_t)secondary_boot, sizeof(u32));
+	if (!boot_reg) {
+		pr_err("unable to map boot register for cpu %u\n", cpu_id);
+		return -ENOSYS;
+	}
+
+	/*
+	 * Secondary cores will start in secondary_startup(),
+	 * defined in "arch/arm/kernel/head.S"
+	 */
+	boot_func = virt_to_phys(secondary_startup);
+	BUG_ON(boot_func & BOOT_ADDR_CPUID_MASK);
+	BUG_ON(boot_func > (phys_addr_t)U32_MAX);
+
+	/* The core to start is encoded in the low bits */
+	boot_val = (u32)boot_func | cpu_id;
+	writel_relaxed(boot_val, boot_reg);
+
+	sev();
+
+	/* The low bits will be cleared once the core has started */
+	start_clock = local_clock();
+	while (!timeout && readl_relaxed(boot_reg) == boot_val)
+		timeout = local_clock() - start_clock > SECONDARY_TIMEOUT_NS;
+
+	iounmap(boot_reg);
+
+	if (!timeout)
+		return 0;
+
+	pr_err("timeout waiting for cpu %u to start\n", cpu_id);
+
+	return -ENOSYS;
+}
+
+static struct smp_operations bcm_smp_ops __initdata = {
+	.smp_prepare_cpus	= bcm_smp_prepare_cpus,
+	.smp_boot_secondary	= bcm_boot_secondary,
+};
+CPU_METHOD_OF_DECLARE(bcm_smp_bcm281xx, "brcm,bcm11351-cpu-method",
+			&bcm_smp_ops);