arch/arm/common/bL_switcher.c - linux - Git at Google

 /*
  * arch/arm/common/bL_switcher.c -- big.LITTLE cluster switcher core driver
  *
  * Created by:	Nicolas Pitre, March 2012
  * Copyright:	(C) 2012-2013  Linaro Limited
  *
  * 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/init.h>
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/sched.h>
 #include <linux/interrupt.h>
 #include <linux/cpu_pm.h>
 #include <linux/workqueue.h>
 #include <linux/mm.h>
 #include <linux/string.h>
 #include <linux/irqchip/arm-gic.h>

 #include <asm/smp_plat.h>
 #include <asm/suspend.h>
 #include <asm/mcpm.h>
 #include <asm/bL_switcher.h>


 /*
  * Use our own MPIDR accessors as the generic ones in asm/cputype.h have
  * __attribute_const__ and we don't want the compiler to assume any
  * constness here as the value _does_ change along some code paths.
  */

 static int read_mpidr(void)
 {
 	unsigned int id;
 	asm volatile ("mrc p15, 0, %0, c0, c0, 5" : "=r" (id));
 	return id & MPIDR_HWID_BITMASK;
 }

 /*
  * bL switcher core code.
  */

 static void bL_do_switch(void *_unused)
 {
 	unsigned mpidr, cpuid, clusterid, ob_cluster, ib_cluster;

 	/*
 	 * We now have a piece of stack borrowed from the init task's.
 	 * Let's also switch to init_mm right away to match it.
 	 */
 	cpu_switch_mm(init_mm.pgd, &init_mm);

 	pr_debug("%s\n", __func__);

 	mpidr = read_mpidr();
 	cpuid = MPIDR_AFFINITY_LEVEL(mpidr, 0);
 	clusterid = MPIDR_AFFINITY_LEVEL(mpidr, 1);
 	ob_cluster = clusterid;
 	ib_cluster = clusterid ^ 1;

 	/*
 	 * Our state has been saved at this point.  Let's release our
 	 * inbound CPU.
 	 */
 	mcpm_set_entry_vector(cpuid, ib_cluster, cpu_resume);
 	sev();

 	/*
 	 * From this point, we must assume that our counterpart CPU might
 	 * have taken over in its parallel world already, as if execution
 	 * just returned from cpu_suspend().  It is therefore important to
 	 * be very careful not to make any change the other guy is not
 	 * expecting.  This is why we need stack isolation.
 	 *
 	 * Fancy under cover tasks could be performed here.  For now
 	 * we have none.
 	 */

 	/* Let's put ourself down. */
 	mcpm_cpu_power_down();

 	/* should never get here */
 	BUG();
 }

 /*
  * Stack isolation.  To ensure 'current' remains valid, we just borrow
  * a slice of the init/idle task which should be fairly lightly used.
  * The borrowed area starts just above the thread_info structure located
  * at the very bottom of the stack, aligned to a cache line.
  */
 #define STACK_SIZE 256
 extern void call_with_stack(void (*fn)(void *), void *arg, void *sp);
 static int bL_switchpoint(unsigned long _arg)
 {
 	unsigned int mpidr = read_mpidr();
 	unsigned int cpuid = MPIDR_AFFINITY_LEVEL(mpidr, 0);
 	unsigned int clusterid = MPIDR_AFFINITY_LEVEL(mpidr, 1);
 	unsigned int cpu_index = cpuid + clusterid * MAX_CPUS_PER_CLUSTER;
 	void *stack = &init_thread_info + 1;
 	stack = PTR_ALIGN(stack, L1_CACHE_BYTES);
 	stack += cpu_index * STACK_SIZE + STACK_SIZE;
 	call_with_stack(bL_do_switch, (void *)_arg, stack);
 	BUG();
 }

 /*
  * Generic switcher interface
  */

 /*
  * bL_switch_to - Switch to a specific cluster for the current CPU
  * @new_cluster_id: the ID of the cluster to switch to.
  *
  * This function must be called on the CPU to be switched.
  * Returns 0 on success, else a negative status code.
  */
 static int bL_switch_to(unsigned int new_cluster_id)
 {
 	unsigned int mpidr, cpuid, clusterid, ob_cluster, ib_cluster, this_cpu;
 	int ret;

 	mpidr = read_mpidr();
 	cpuid = MPIDR_AFFINITY_LEVEL(mpidr, 0);
 	clusterid = MPIDR_AFFINITY_LEVEL(mpidr, 1);
 	ob_cluster = clusterid;
 	ib_cluster = clusterid ^ 1;

 	if (new_cluster_id == clusterid)
 		return 0;

 	pr_debug("before switch: CPU %d in cluster %d\n", cpuid, clusterid);

 	/* Close the gate for our entry vectors */
 	mcpm_set_entry_vector(cpuid, ob_cluster, NULL);
 	mcpm_set_entry_vector(cpuid, ib_cluster, NULL);

 	/*
 	 * Let's wake up the inbound CPU now in case it requires some delay
 	 * to come online, but leave it gated in our entry vector code.
 	 */
 	ret = mcpm_cpu_power_up(cpuid, ib_cluster);
 	if (ret) {
 		pr_err("%s: mcpm_cpu_power_up() returned %d\n", __func__, ret);
 		return ret;
 	}

 	/*
 	 * From this point we are entering the switch critical zone
 	 * and can't take any interrupts anymore.
 	 */
 	local_irq_disable();
 	local_fiq_disable();

 	this_cpu = smp_processor_id();

 	/* redirect GIC's SGIs to our counterpart */
 	gic_migrate_target(cpuid + ib_cluster*4);

 	/*
 	 * Raise a SGI on the inbound CPU to make sure it doesn't stall
 	 * in a possible WFI, such as in mcpm_power_down().
 	 */
 	arch_send_wakeup_ipi_mask(cpumask_of(this_cpu));

 	ret = cpu_pm_enter();

 	/* we can not tolerate errors at this point */
 	if (ret)
 		panic("%s: cpu_pm_enter() returned %d\n", __func__, ret);

 	/* Flip the cluster in the CPU logical map for this CPU. */
 	cpu_logical_map(this_cpu) ^= (1 << 8);

 	/* Let's do the actual CPU switch. */
 	ret = cpu_suspend(0, bL_switchpoint);
 	if (ret > 0)
 		panic("%s: cpu_suspend() returned %d\n", __func__, ret);

 	/* We are executing on the inbound CPU at this point */
 	mpidr = read_mpidr();
 	cpuid = MPIDR_AFFINITY_LEVEL(mpidr, 0);
 	clusterid = MPIDR_AFFINITY_LEVEL(mpidr, 1);
 	pr_debug("after switch: CPU %d in cluster %d\n", cpuid, clusterid);
 	BUG_ON(clusterid != ib_cluster);

 	mcpm_cpu_powered_up();

 	ret = cpu_pm_exit();

 	local_fiq_enable();
 	local_irq_enable();

 	if (ret)
 		pr_err("%s exiting with error %d\n", __func__, ret);
 	return ret;
 }

 struct switch_args {
 	unsigned int cluster;
 	struct work_struct work;
 };

 static void __bL_switch_to(struct work_struct *work)
 {
 	struct switch_args *args = container_of(work, struct switch_args, work);
 	bL_switch_to(args->cluster);
 }

 /*
  * bL_switch_request - Switch to a specific cluster for the given CPU
  *
  * @cpu: the CPU to switch
  * @new_cluster_id: the ID of the cluster to switch to.
  *
  * This function causes a cluster switch on the given CPU.  If the given
  * CPU is the same as the calling CPU then the switch happens right away.
  * Otherwise the request is put on a work queue to be scheduled on the
  * remote CPU.
  */
 void bL_switch_request(unsigned int cpu, unsigned int new_cluster_id)
 {
 	unsigned int this_cpu = get_cpu();
 	struct switch_args args;

 	if (cpu == this_cpu) {
 		bL_switch_to(new_cluster_id);
 		put_cpu();
 		return;
 	}
 	put_cpu();

 	args.cluster = new_cluster_id;
 	INIT_WORK_ONSTACK(&args.work, __bL_switch_to);
 	schedule_work_on(cpu, &args.work);
 	flush_work(&args.work);
 }
 EXPORT_SYMBOL_GPL(bL_switch_request);
	/*
	* arch/arm/common/bL_switcher.c -- big.LITTLE cluster switcher core driver
	*
	* Created by: Nicolas Pitre, March 2012
	* Copyright: (C) 2012-2013 Linaro Limited
	*
	* 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/init.h>
	#include <linux/kernel.h>
	#include <linux/module.h>
	#include <linux/sched.h>
	#include <linux/interrupt.h>
	#include <linux/cpu_pm.h>
	#include <linux/workqueue.h>
	#include <linux/mm.h>
	#include <linux/string.h>
	#include <linux/irqchip/arm-gic.h>

	#include <asm/smp_plat.h>
	#include <asm/suspend.h>
	#include <asm/mcpm.h>
	#include <asm/bL_switcher.h>


	/*
	* Use our own MPIDR accessors as the generic ones in asm/cputype.h have
	* __attribute_const__ and we don't want the compiler to assume any
	* constness here as the value _does_ change along some code paths.
	*/

	static int read_mpidr(void)
	{
	unsigned int id;
	asm volatile ("mrc p15, 0, %0, c0, c0, 5" : "=r" (id));
	return id & MPIDR_HWID_BITMASK;
	}

	/*
	* bL switcher core code.
	*/

	static void bL_do_switch(void *_unused)
	{
	unsigned mpidr, cpuid, clusterid, ob_cluster, ib_cluster;

	/*
	* We now have a piece of stack borrowed from the init task's.
	* Let's also switch to init_mm right away to match it.
	*/
	cpu_switch_mm(init_mm.pgd, &init_mm);

	pr_debug("%s\n", __func__);

	mpidr = read_mpidr();
	cpuid = MPIDR_AFFINITY_LEVEL(mpidr, 0);
	clusterid = MPIDR_AFFINITY_LEVEL(mpidr, 1);
	ob_cluster = clusterid;
	ib_cluster = clusterid ^ 1;

	/*
	* Our state has been saved at this point. Let's release our
	* inbound CPU.
	*/
	mcpm_set_entry_vector(cpuid, ib_cluster, cpu_resume);
	sev();

	/*
	* From this point, we must assume that our counterpart CPU might
	* have taken over in its parallel world already, as if execution
	* just returned from cpu_suspend(). It is therefore important to
	* be very careful not to make any change the other guy is not
	* expecting. This is why we need stack isolation.
	*
	* Fancy under cover tasks could be performed here. For now
	* we have none.
	*/

	/* Let's put ourself down. */
	mcpm_cpu_power_down();

	/* should never get here */
	BUG();
	}

	/*
	* Stack isolation. To ensure 'current' remains valid, we just borrow
	* a slice of the init/idle task which should be fairly lightly used.
	* The borrowed area starts just above the thread_info structure located
	* at the very bottom of the stack, aligned to a cache line.
	*/
	#define STACK_SIZE 256
	extern void call_with_stack(void (fn)(void ), void arg, void sp);
	static int bL_switchpoint(unsigned long _arg)
	{
	unsigned int mpidr = read_mpidr();
	unsigned int cpuid = MPIDR_AFFINITY_LEVEL(mpidr, 0);
	unsigned int clusterid = MPIDR_AFFINITY_LEVEL(mpidr, 1);
	unsigned int cpu_index = cpuid + clusterid * MAX_CPUS_PER_CLUSTER;
	void *stack = &init_thread_info + 1;
	stack = PTR_ALIGN(stack, L1_CACHE_BYTES);
	stack += cpu_index * STACK_SIZE + STACK_SIZE;
	call_with_stack(bL_do_switch, (void *)_arg, stack);
	BUG();
	}

	/*
	* Generic switcher interface
	*/

	/*
	* bL_switch_to - Switch to a specific cluster for the current CPU
	* @new_cluster_id: the ID of the cluster to switch to.
	*
	* This function must be called on the CPU to be switched.
	* Returns 0 on success, else a negative status code.
	*/
	static int bL_switch_to(unsigned int new_cluster_id)
	{
	unsigned int mpidr, cpuid, clusterid, ob_cluster, ib_cluster, this_cpu;
	int ret;

	mpidr = read_mpidr();
	cpuid = MPIDR_AFFINITY_LEVEL(mpidr, 0);
	clusterid = MPIDR_AFFINITY_LEVEL(mpidr, 1);
	ob_cluster = clusterid;
	ib_cluster = clusterid ^ 1;

	if (new_cluster_id == clusterid)
	return 0;

	pr_debug("before switch: CPU %d in cluster %d\n", cpuid, clusterid);

	/* Close the gate for our entry vectors */
	mcpm_set_entry_vector(cpuid, ob_cluster, NULL);
	mcpm_set_entry_vector(cpuid, ib_cluster, NULL);

	/*
	* Let's wake up the inbound CPU now in case it requires some delay
	* to come online, but leave it gated in our entry vector code.
	*/
	ret = mcpm_cpu_power_up(cpuid, ib_cluster);
	if (ret) {
	pr_err("%s: mcpm_cpu_power_up() returned %d\n", __func__, ret);
	return ret;
	}

	/*
	* From this point we are entering the switch critical zone
	* and can't take any interrupts anymore.
	*/
	local_irq_disable();
	local_fiq_disable();

	this_cpu = smp_processor_id();

	/* redirect GIC's SGIs to our counterpart */
	gic_migrate_target(cpuid + ib_cluster*4);

	/*
	* Raise a SGI on the inbound CPU to make sure it doesn't stall
	* in a possible WFI, such as in mcpm_power_down().
	*/
	arch_send_wakeup_ipi_mask(cpumask_of(this_cpu));

	ret = cpu_pm_enter();

	/* we can not tolerate errors at this point */
	if (ret)
	panic("%s: cpu_pm_enter() returned %d\n", __func__, ret);

	/* Flip the cluster in the CPU logical map for this CPU. */
	cpu_logical_map(this_cpu) ^= (1 << 8);

	/* Let's do the actual CPU switch. */
	ret = cpu_suspend(0, bL_switchpoint);
	if (ret > 0)
	panic("%s: cpu_suspend() returned %d\n", __func__, ret);

	/* We are executing on the inbound CPU at this point */
	mpidr = read_mpidr();
	cpuid = MPIDR_AFFINITY_LEVEL(mpidr, 0);
	clusterid = MPIDR_AFFINITY_LEVEL(mpidr, 1);
	pr_debug("after switch: CPU %d in cluster %d\n", cpuid, clusterid);
	BUG_ON(clusterid != ib_cluster);

	mcpm_cpu_powered_up();

	ret = cpu_pm_exit();

	local_fiq_enable();
	local_irq_enable();

	if (ret)
	pr_err("%s exiting with error %d\n", __func__, ret);
	return ret;
	}

	struct switch_args {
	unsigned int cluster;
	struct work_struct work;
	};

	static void __bL_switch_to(struct work_struct *work)
	{
	struct switch_args *args = container_of(work, struct switch_args, work);
	bL_switch_to(args->cluster);
	}

	/*
	* bL_switch_request - Switch to a specific cluster for the given CPU
	*
	* @cpu: the CPU to switch
	* @new_cluster_id: the ID of the cluster to switch to.
	*
	* This function causes a cluster switch on the given CPU. If the given
	* CPU is the same as the calling CPU then the switch happens right away.
	* Otherwise the request is put on a work queue to be scheduled on the
	* remote CPU.
	*/
	void bL_switch_request(unsigned int cpu, unsigned int new_cluster_id)
	{
	unsigned int this_cpu = get_cpu();
	struct switch_args args;

	if (cpu == this_cpu) {
	bL_switch_to(new_cluster_id);
	put_cpu();
	return;
	}
	put_cpu();

	args.cluster = new_cluster_id;
	INIT_WORK_ONSTACK(&args.work, __bL_switch_to);
	schedule_work_on(cpu, &args.work);
	flush_work(&args.work);
	}
	EXPORT_SYMBOL_GPL(bL_switch_request);