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+/*
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+ * arch/arm/common/bL_switcher.c -- big.LITTLE cluster switcher core driver
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+ *
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+ * Created by: Nicolas Pitre, March 2012
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+ * Copyright: (C) 2012-2013 Linaro Limited
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+ *
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+ * This program is free software; you can redistribute it and/or modify
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+ * it under the terms of the GNU General Public License version 2 as
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+ * published by the Free Software Foundation.
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+ */
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+
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+#include <linux/init.h>
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+#include <linux/kernel.h>
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+#include <linux/module.h>
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+#include <linux/sched.h>
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+#include <linux/interrupt.h>
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+#include <linux/cpu_pm.h>
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+#include <linux/workqueue.h>
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+#include <linux/mm.h>
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+#include <linux/string.h>
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+#include <linux/irqchip/arm-gic.h>
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+
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+#include <asm/smp_plat.h>
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+#include <asm/suspend.h>
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+#include <asm/mcpm.h>
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+#include <asm/bL_switcher.h>
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+
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+
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+/*
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+ * Use our own MPIDR accessors as the generic ones in asm/cputype.h have
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+ * __attribute_const__ and we don't want the compiler to assume any
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+ * constness here as the value _does_ change along some code paths.
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+ */
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+
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+static int read_mpidr(void)
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+{
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+ unsigned int id;
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+ asm volatile ("mrc p15, 0, %0, c0, c0, 5" : "=r" (id));
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+ return id & MPIDR_HWID_BITMASK;
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+}
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+
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+/*
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+ * bL switcher core code.
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+ */
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+
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+static void bL_do_switch(void *_unused)
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+{
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+ unsigned mpidr, cpuid, clusterid, ob_cluster, ib_cluster;
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+
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+ /*
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+ * We now have a piece of stack borrowed from the init task's.
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+ * Let's also switch to init_mm right away to match it.
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+ */
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+ cpu_switch_mm(init_mm.pgd, &init_mm);
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+
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+ pr_debug("%s\n", __func__);
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+
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+ mpidr = read_mpidr();
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+ cpuid = MPIDR_AFFINITY_LEVEL(mpidr, 0);
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+ clusterid = MPIDR_AFFINITY_LEVEL(mpidr, 1);
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+ ob_cluster = clusterid;
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+ ib_cluster = clusterid ^ 1;
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+
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+ /*
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+ * Our state has been saved at this point. Let's release our
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+ * inbound CPU.
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+ */
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+ mcpm_set_entry_vector(cpuid, ib_cluster, cpu_resume);
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+ sev();
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+
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+ /*
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+ * From this point, we must assume that our counterpart CPU might
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+ * have taken over in its parallel world already, as if execution
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+ * just returned from cpu_suspend(). It is therefore important to
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+ * be very careful not to make any change the other guy is not
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+ * expecting. This is why we need stack isolation.
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+ *
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+ * Fancy under cover tasks could be performed here. For now
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+ * we have none.
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+ */
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+
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+ /* Let's put ourself down. */
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+ mcpm_cpu_power_down();
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+
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+ /* should never get here */
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+ BUG();
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+}
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+
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+/*
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+ * Stack isolation. To ensure 'current' remains valid, we just borrow
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+ * a slice of the init/idle task which should be fairly lightly used.
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+ * The borrowed area starts just above the thread_info structure located
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+ * at the very bottom of the stack, aligned to a cache line.
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+ */
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+#define STACK_SIZE 256
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+extern void call_with_stack(void (*fn)(void *), void *arg, void *sp);
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+static int bL_switchpoint(unsigned long _arg)
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+{
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+ unsigned int mpidr = read_mpidr();
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+ unsigned int cpuid = MPIDR_AFFINITY_LEVEL(mpidr, 0);
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+ unsigned int clusterid = MPIDR_AFFINITY_LEVEL(mpidr, 1);
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+ unsigned int cpu_index = cpuid + clusterid * MAX_CPUS_PER_CLUSTER;
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+ void *stack = &init_thread_info + 1;
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+ stack = PTR_ALIGN(stack, L1_CACHE_BYTES);
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+ stack += cpu_index * STACK_SIZE + STACK_SIZE;
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+ call_with_stack(bL_do_switch, (void *)_arg, stack);
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+ BUG();
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+}
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+
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+/*
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+ * Generic switcher interface
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+ */
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+
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+/*
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+ * bL_switch_to - Switch to a specific cluster for the current CPU
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+ * @new_cluster_id: the ID of the cluster to switch to.
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+ *
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+ * This function must be called on the CPU to be switched.
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+ * Returns 0 on success, else a negative status code.
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+ */
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+static int bL_switch_to(unsigned int new_cluster_id)
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+{
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+ unsigned int mpidr, cpuid, clusterid, ob_cluster, ib_cluster, this_cpu;
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+ int ret;
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+
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+ mpidr = read_mpidr();
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+ cpuid = MPIDR_AFFINITY_LEVEL(mpidr, 0);
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+ clusterid = MPIDR_AFFINITY_LEVEL(mpidr, 1);
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+ ob_cluster = clusterid;
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+ ib_cluster = clusterid ^ 1;
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+
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+ if (new_cluster_id == clusterid)
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+ return 0;
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+
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+ pr_debug("before switch: CPU %d in cluster %d\n", cpuid, clusterid);
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+
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+ /* Close the gate for our entry vectors */
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+ mcpm_set_entry_vector(cpuid, ob_cluster, NULL);
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+ mcpm_set_entry_vector(cpuid, ib_cluster, NULL);
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+
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+ /*
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+ * Let's wake up the inbound CPU now in case it requires some delay
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+ * to come online, but leave it gated in our entry vector code.
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+ */
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+ ret = mcpm_cpu_power_up(cpuid, ib_cluster);
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+ if (ret) {
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+ pr_err("%s: mcpm_cpu_power_up() returned %d\n", __func__, ret);
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+ return ret;
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+ }
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+
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+ /*
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+ * From this point we are entering the switch critical zone
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+ * and can't take any interrupts anymore.
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+ */
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+ local_irq_disable();
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+ local_fiq_disable();
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+
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+ this_cpu = smp_processor_id();
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+
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+ /* redirect GIC's SGIs to our counterpart */
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+ gic_migrate_target(cpuid + ib_cluster*4);
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+
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+ /*
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+ * Raise a SGI on the inbound CPU to make sure it doesn't stall
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+ * in a possible WFI, such as in mcpm_power_down().
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+ */
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+ arch_send_wakeup_ipi_mask(cpumask_of(this_cpu));
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+
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+ ret = cpu_pm_enter();
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+
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+ /* we can not tolerate errors at this point */
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+ if (ret)
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+ panic("%s: cpu_pm_enter() returned %d\n", __func__, ret);
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+
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+ /* Flip the cluster in the CPU logical map for this CPU. */
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+ cpu_logical_map(this_cpu) ^= (1 << 8);
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+
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+ /* Let's do the actual CPU switch. */
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+ ret = cpu_suspend(0, bL_switchpoint);
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+ if (ret > 0)
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+ panic("%s: cpu_suspend() returned %d\n", __func__, ret);
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+
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+ /* We are executing on the inbound CPU at this point */
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+ mpidr = read_mpidr();
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+ cpuid = MPIDR_AFFINITY_LEVEL(mpidr, 0);
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+ clusterid = MPIDR_AFFINITY_LEVEL(mpidr, 1);
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+ pr_debug("after switch: CPU %d in cluster %d\n", cpuid, clusterid);
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+ BUG_ON(clusterid != ib_cluster);
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+
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+ mcpm_cpu_powered_up();
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+
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+ ret = cpu_pm_exit();
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+
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+ local_fiq_enable();
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+ local_irq_enable();
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+
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+ if (ret)
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+ pr_err("%s exiting with error %d\n", __func__, ret);
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+ return ret;
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+}
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+
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+struct switch_args {
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+ unsigned int cluster;
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+ struct work_struct work;
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+};
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+
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+static void __bL_switch_to(struct work_struct *work)
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+{
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+ struct switch_args *args = container_of(work, struct switch_args, work);
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+ bL_switch_to(args->cluster);
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+}
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+
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+/*
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+ * bL_switch_request - Switch to a specific cluster for the given CPU
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+ *
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+ * @cpu: the CPU to switch
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+ * @new_cluster_id: the ID of the cluster to switch to.
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+ *
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+ * This function causes a cluster switch on the given CPU. If the given
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+ * CPU is the same as the calling CPU then the switch happens right away.
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+ * Otherwise the request is put on a work queue to be scheduled on the
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+ * remote CPU.
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+ */
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+void bL_switch_request(unsigned int cpu, unsigned int new_cluster_id)
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+{
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+ unsigned int this_cpu = get_cpu();
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+ struct switch_args args;
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+
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+ if (cpu == this_cpu) {
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+ bL_switch_to(new_cluster_id);
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+ put_cpu();
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+ return;
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+ }
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+ put_cpu();
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+
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+ args.cluster = new_cluster_id;
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+ INIT_WORK_ONSTACK(&args.work, __bL_switch_to);
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+ schedule_work_on(cpu, &args.work);
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+ flush_work(&args.work);
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+}
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+EXPORT_SYMBOL_GPL(bL_switch_request);
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Nicolas Pitre