[RFC PATCH 2/2] ARM: SMP support for mach-virt

[will.deacon@arm.com (Will Deacon)]

From: Marc Zyngier <marc.zyngier@arm.com>

This patch adds support for SMP to mach-virt.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
---
 arch/arm/mach-virt/Makefile  |   1 +
 arch/arm/mach-virt/headsmp.S |  38 ++++++++
 arch/arm/mach-virt/platsmp.c | 205 +++++++++++++++++++++++++++++++++++++++++++
 arch/arm/mach-virt/virt.c    |   6 ++
 4 files changed, 250 insertions(+)
 create mode 100644 arch/arm/mach-virt/headsmp.S
 create mode 100644 arch/arm/mach-virt/platsmp.c

diff --git a/arch/arm/mach-virt/Makefile b/arch/arm/mach-virt/Makefile
index 7ddbfa6..9ce8a28 100644
--- a/arch/arm/mach-virt/Makefile
+++ b/arch/arm/mach-virt/Makefile
@@ -3,3 +3,4 @@
 #
 
 obj-y					:= virt.o
+obj-$(CONFIG_SMP)			+= platsmp.o headsmp.o
diff --git a/arch/arm/mach-virt/headsmp.S b/arch/arm/mach-virt/headsmp.S
new file mode 100644
index 0000000..e27afb0
--- /dev/null
+++ b/arch/arm/mach-virt/headsmp.S
@@ -0,0 +1,38 @@
+/*
+ *  Copyright (c) 2012 ARM Limited
+ *  All Rights Reserved
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+#include <linux/linkage.h>
+#include <linux/init.h>
+
+	__INIT
+
+/*
+ * This provides a "holding pen" into which all secondary cores are held
+ * until we're ready for them to initialise.
+ */
+ENTRY(virt_secondary_startup)
+	mrc	p15, 0, r0, c0, c0, 5
+	and	r0, r0, #15
+	adr	r4, 1f
+	ldmia	r4, {r5, r6}
+	sub	r4, r4, r5
+	add	r6, r6, r4
+pen:	ldr	r7, [r6]
+	cmp	r7, r0
+	bne	pen
+
+	/*
+	 * we've been released from the holding pen: secondary_stack
+	 * should now contain the SVC stack for this core
+	 */
+	b	secondary_startup
+
+	.align
+1:	.long	.
+	.long	pen_release
+ENDPROC(virt_secondary_startup)
diff --git a/arch/arm/mach-virt/platsmp.c b/arch/arm/mach-virt/platsmp.c
new file mode 100644
index 0000000..fe02f51
--- /dev/null
+++ b/arch/arm/mach-virt/platsmp.c
@@ -0,0 +1,205 @@
+/*
+ * Dummy Virtual Machine - does what it says on the tin.
+ *
+ * SMP operations, shamelessly stolen from:
+ * arch/arm64/kernel/smp.c
+ *
+ * Copyright (C) 2012 ARM Ltd
+ * Author: Catalin Marinas <catalin.marinas@arm.com>
+ * Author: Will Deacon <will.deacon@arm.com>
+ * Author: Marc Zyngier <marc.zyngier@arm.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <linux/smp.h>
+#include <linux/errno.h>
+#include <linux/delay.h>
+#include <linux/device.h>
+#include <linux/jiffies.h>
+#include <linux/of.h>
+
+#include <asm/cacheflush.h>
+#include <asm/smp_plat.h>
+#include <asm/hardware/gic.h>
+
+extern void virt_secondary_startup(void);
+
+static DEFINE_RAW_SPINLOCK(boot_lock);
+static phys_addr_t cpu_release_addr[NR_CPUS];
+
+/*
+ * Write secondary_holding_pen_release in a way that is guaranteed to be
+ * visible to all observers, irrespective of whether they're taking part
+ * in coherency or not.  This is necessary for the hotplug code to work
+ * reliably.
+ */
+static void __cpuinit write_pen_release(int val)
+{
+	void *start = (void *)&pen_release;
+	unsigned long size = sizeof(pen_release);
+
+	pen_release = val;
+	smp_wmb();
+	__cpuc_flush_dcache_area(start, size);
+	outer_clean_range(__pa(&pen_release), __pa(&pen_release + 1));
+}
+
+/*
+ * Enumerate the possible CPU set from the device tree.
+ */
+static void __init virt_smp_init_cpus(void)
+{
+	const char *enable_method;
+	struct device_node *dn = NULL;
+	int cpu = 0;
+	u32 release_addr;
+
+	while ((dn = of_find_node_by_type(dn, "cpu"))) {
+		if (cpu >= NR_CPUS)
+			goto next;
+
+		/*
+		 * We currently support only the "spin-table" enable-method.
+		 */
+		enable_method = of_get_property(dn, "enable-method", NULL);
+		if (!enable_method || strcmp(enable_method, "spin-table")) {
+			pr_err("CPU %d: missing or invalid enable-method property: %s\n",
+			       cpu, enable_method);
+			goto next;
+		}
+
+		/*
+		 * Determine the address from which the CPU is polling.
+		 */
+		if (of_property_read_u32(dn, "cpu-release-addr", &release_addr)) {
+			pr_err("CPU %d: missing or invalid cpu-release-addr property\n",
+			       cpu);
+			goto next;
+		}
+
+		cpu_release_addr[cpu] = release_addr;
+		set_cpu_possible(cpu, true);
+next:
+		cpu++;
+	}
+
+	/* sanity check */
+	if (cpu > NR_CPUS)
+		pr_warning("no. of cores (%d) greater than configured maximum of %d - clipping\n",
+			   cpu, NR_CPUS);
+
+	set_smp_cross_call(gic_raise_softirq);
+}
+
+static void __init virt_smp_prepare_cpus(unsigned int max_cpus)
+{
+	int cpu;
+	void **release_addr;
+	unsigned int ncores = num_possible_cpus();
+
+	/*
+	 * are we trying to boot more cores than exist?
+	 */
+	if (max_cpus > ncores)
+		max_cpus = ncores;
+
+	/*
+	 * Initialise the present map (which describes the set of CPUs
+	 * actually populated at the present time) and release the
+	 * secondaries from the bootloader.
+	 */
+	for_each_possible_cpu(cpu) {
+		if (max_cpus == 0)
+			break;
+
+		if (!cpu_release_addr[cpu])
+			continue;
+
+		release_addr = __va(cpu_release_addr[cpu]);
+		release_addr[0] = (void *)__pa(virt_secondary_startup);
+		smp_wmb();
+		__cpuc_flush_dcache_area(release_addr, sizeof(release_addr[0]));
+		outer_clean_range(__pa(release_addr), __pa(release_addr+1));
+
+		set_cpu_present(cpu, true);
+		max_cpus--;
+	}
+}
+
+static int __cpuinit virt_boot_secondary(unsigned int cpu,
+					 struct task_struct *idle)
+{
+	unsigned long timeout;
+
+	/*
+	 * Set synchronisation state between this boot processor
+	 * and the secondary one
+	 */
+	raw_spin_lock(&boot_lock);
+
+	/*
+	 * Update the pen release flag.
+	 */
+	write_pen_release(cpu);
+
+	/*
+	 * Send the secondary CPU a soft interrupt, causing the
+	 * secondaries to read pen_release.
+	 */
+	gic_raise_softirq(cpumask_of(cpu), 0);
+
+	timeout = jiffies + (1 * HZ);
+	while (time_before(jiffies, timeout)) {
+		if (pen_release == -1UL)
+			break;
+		udelay(10);
+	}
+
+	/*
+	 * Now the secondary core is starting up let it run its
+	 * calibrations, then wait for it to finish
+	 */
+	raw_spin_unlock(&boot_lock);
+
+	return pen_release != -1 ? -ENOSYS : 0;
+}
+
+static void __cpuinit virt_secondary_init(unsigned int cpu)
+{
+	/*
+	 * if any interrupts are already enabled for the primary
+	 * core (e.g. timer irq), then they will not have been enabled
+	 * for us: do so
+	 */
+	gic_secondary_init(0);
+
+	/*
+	 * let the primary processor know we're out of the
+	 * pen, then head off into the C entry point
+	 */
+	write_pen_release(-1);
+
+	/*
+	 * Synchronise with the boot thread.
+	 */
+	raw_spin_lock(&boot_lock);
+	raw_spin_unlock(&boot_lock);
+}
+
+struct smp_operations __initdata virt_smp_ops = {
+	.smp_init_cpus		= virt_smp_init_cpus,
+	.smp_prepare_cpus	= virt_smp_prepare_cpus,
+	.smp_secondary_init	= virt_secondary_init,
+	.smp_boot_secondary	= virt_boot_secondary,
+};
diff --git a/arch/arm/mach-virt/virt.c b/arch/arm/mach-virt/virt.c
index 174b9da..d764835 100644
--- a/arch/arm/mach-virt/virt.c
+++ b/arch/arm/mach-virt/virt.c
@@ -20,6 +20,7 @@
 
 #include <linux/of_irq.h>
 #include <linux/of_platform.h>
+#include <linux/smp.h>
 
 #include <asm/arch_timer.h>
 #include <asm/hardware/gic.h>
@@ -56,10 +57,15 @@ static struct sys_timer virt_timer = {
 	.init = virt_timer_init,
 };
 
+#ifdef CONFIG_SMP
+extern struct smp_operations virt_smp_ops;
+#endif
+
 DT_MACHINE_START(VIRT, "Dummy Virtual Machine")
 	.init_irq	= gic_init_irq,
 	.handle_irq     = gic_handle_irq,
 	.timer		= &virt_timer,
 	.init_machine	= virt_init,
+	.smp		= smp_ops(virt_smp_ops),
 	.dt_compat	= virt_dt_match,
 MACHINE_END
-- 
1.8.0