[RFC PATCH 2/2] ARM: SMP support for mach-virt
Rob Herring
robherring2 at gmail.com
Mon Dec 3 16:55:35 EST 2012
On 12/03/2012 11:52 AM, Will Deacon wrote:
> From: Marc Zyngier <marc.zyngier at arm.com>
>
> This patch adds support for SMP to mach-virt.
>
> Signed-off-by: Marc Zyngier <marc.zyngier at arm.com>
> Signed-off-by: Will Deacon <will.deacon at 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
Why is the pen is needed? It should only be needed for hotplug on
systems that can't reset their cores. I'd hope you could design good
virtual h/w.
> +
> + /*
> + * 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 at arm.com>
> + * Author: Will Deacon <will.deacon at arm.com>
> + * Author: Marc Zyngier <marc.zyngier at 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")) {
Are these documented?
> + 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
>
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