sh: add SMP support for J2

Support is hooked up via a cpu start method specified in the device
tree, and also depends on DT nodes that describe the interfaces for
performing IPI and identifying which cpu execution is taking place on.
The currently used method is a form of spin table, where secondary
cpus are unblocked by writing to a special address.

Signed-off-by: Rich Felker <dalias@libc.org>

arch/sh/Kconfig

@@ -261,6 +261,8 @@ config CPU_SUBTYPE_SH7619
 config CPU_SUBTYPE_J2
 	bool "Support J2 processor"
 	select CPU_J2
+	select SYS_SUPPORTS_SMP
+	select GENERIC_CLOCKEVENTS_BROADCAST if SMP
 
 # SH-2A Processor Support
 

arch/sh/kernel/cpu/sh2/Makefile

@@ -5,3 +5,7 @@
 obj-y	:= ex.o probe.o entry.o
 
 obj-$(CONFIG_CPU_SUBTYPE_SH7619) += setup-sh7619.o clock-sh7619.o
+
+# SMP setup
+smp-$(CONFIG_CPU_J2)			:= smp-j2.o
+obj-$(CONFIG_SMP)			+= $(smp-y)

arch/sh/kernel/cpu/sh2/smp-j2.c

@@ -0,0 +1,139 @@
+/*
+ * SMP support for J2 processor
+ *
+ * Copyright (C) 2015-2016 Smart Energy Instruments, Inc.
+ *
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License.  See the file "COPYING" in the main directory of this archive
+ * for more details.
+ */
+
+#include <linux/smp.h>
+#include <linux/interrupt.h>
+#include <linux/io.h>
+#include <linux/of_address.h>
+#include <linux/of_irq.h>
+#include <asm/cmpxchg.h>
+
+DEFINE_PER_CPU(unsigned, j2_ipi_messages);
+
+extern u32 *sh2_cpuid_addr;
+static u32 *j2_ipi_trigger;
+static int j2_ipi_irq;
+
+static irqreturn_t j2_ipi_interrupt_handler(int irq, void *arg)
+{
+	unsigned cpu = hard_smp_processor_id();
+	volatile unsigned *pmsg = &per_cpu(j2_ipi_messages, cpu);
+	unsigned messages, i;
+
+	do messages = *pmsg;
+	while (cmpxchg(pmsg, messages, 0) != messages);
+
+	if (!messages) return IRQ_NONE;
+
+	for (i=0; i<SMP_MSG_NR; i++)
+		if (messages & (1U<<i))
+			smp_message_recv(i);
+
+	return IRQ_HANDLED;
+}
+
+static void j2_smp_setup(void)
+{
+}
+
+static void j2_prepare_cpus(unsigned int max_cpus)
+{
+	struct device_node *np;
+	unsigned i, max = 1;
+
+	np = of_find_compatible_node(NULL, NULL, "jcore,ipi-controller");
+	if (!np)
+		goto out;
+
+	j2_ipi_irq = irq_of_parse_and_map(np, 0);
+	j2_ipi_trigger = of_iomap(np, 0);
+	if (!j2_ipi_irq || !j2_ipi_trigger)
+		goto out;
+
+	np = of_find_compatible_node(NULL, NULL, "jcore,cpuid-mmio");
+	if (!np)
+		goto out;
+
+	sh2_cpuid_addr = of_iomap(np, 0);
+	if (!sh2_cpuid_addr)
+		goto out;
+
+	if (request_irq(j2_ipi_irq, j2_ipi_interrupt_handler, IRQF_PERCPU,
+			"ipi", (void *)j2_ipi_interrupt_handler) != 0)
+		goto out;
+
+	max = max_cpus;
+out:
+	/* Disable any cpus past max_cpus, or all secondaries if we didn't
+	 * get the necessary resources to support SMP. */
+	for (i=max; i<NR_CPUS; i++) {
+		set_cpu_possible(i, false);
+		set_cpu_present(i, false);
+	}
+}
+
+static void j2_start_cpu(unsigned int cpu, unsigned long entry_point)
+{
+	struct device_node *np;
+	u32 regs[2];
+	void __iomem *release, *initpc;
+
+	if (!cpu) return;
+
+	np = of_get_cpu_node(cpu, NULL);
+	if (!np) return;
+
+	if (of_property_read_u32_array(np, "cpu-release-addr", regs, 2)) return;
+	release = ioremap_nocache(regs[0], sizeof(u32));
+	initpc = ioremap_nocache(regs[1], sizeof(u32));
+
+	__raw_writel(entry_point, initpc);
+	__raw_writel(1, release);
+
+	iounmap(initpc);
+	iounmap(release);
+
+	pr_info("J2 SMP: requested start of cpu %u\n", cpu);
+}
+
+static unsigned int j2_smp_processor_id(void)
+{
+	return __raw_readl(sh2_cpuid_addr);
+}
+
+static void j2_send_ipi(unsigned int cpu, unsigned int message)
+{
+	volatile unsigned *pmsg;
+	unsigned old;
+	unsigned long val;
+
+	/* There is only one IPI interrupt shared by all messages, so
+	 * we keep a separate interrupt flag per message type in sw. */
+	pmsg = &per_cpu(j2_ipi_messages, cpu);
+	do old = *pmsg;
+	while (cmpxchg(pmsg, old, old|(1U<<message)) != old);
+
+	/* Generate the actual interrupt by writing to CCRn bit 28. */
+	val = __raw_readl(j2_ipi_trigger + cpu);
+	__raw_writel(val | (1U<<28), j2_ipi_trigger + cpu);
+}
+
+static struct plat_smp_ops j2_smp_ops = {
+	.smp_setup		= j2_smp_setup,
+	.prepare_cpus		= j2_prepare_cpus,
+	.start_cpu		= j2_start_cpu,
+	.smp_processor_id	= j2_smp_processor_id,
+	.send_ipi		= j2_send_ipi,
+	.cpu_die		= native_cpu_die,
+	.cpu_disable		= native_cpu_disable,
+	.play_dead		= native_play_dead,
+};
+
+CPU_METHOD_OF_DECLARE(j2_cpu_method, "jcore,spin-table", &j2_smp_ops);