arch/arm/common/bL_switcher.c

   1 /*
   2  * arch/arm/common/bL_switcher.c -- big.LITTLE cluster switcher core driver
   3  *
   4  * Created by:  Nicolas Pitre, March 2012
   5  * Copyright:   (C) 2012-2013  Linaro Limited
   6  *
   7  * This program is free software; you can redistribute it and/or modify
   8  * it under the terms of the GNU General Public License version 2 as
   9  * published by the Free Software Foundation.
  10  */
  11
  12 #include <linux/init.h>
  13 #include <linux/kernel.h>
  14 #include <linux/module.h>
  15 #include <linux/sched.h>
  16 #include <linux/interrupt.h>
  17 #include <linux/cpu_pm.h>
  18 #include <linux/workqueue.h>
  19 #include <linux/mm.h>
  20 #include <linux/string.h>
  21 #include <linux/irqchip/arm-gic.h>
  22
  23 #include <asm/smp_plat.h>
  24 #include <asm/suspend.h>
  25 #include <asm/mcpm.h>
  26 #include <asm/bL_switcher.h>
  27
  28
  29 /*
  30  * Use our own MPIDR accessors as the generic ones in asm/cputype.h have
  31  * __attribute_const__ and we don't want the compiler to assume any
  32  * constness here as the value _does_ change along some code paths.
  33  */
  34
  35 static int read_mpidr(void)
  36 {
  37         unsigned int id;
  38         asm volatile ("mrc p15, 0, %0, c0, c0, 5" : "=r" (id));
  39         return id & MPIDR_HWID_BITMASK;
  40 }
  41
  42 /*
  43  * bL switcher core code.
  44  */
  45
  46 static void bL_do_switch(void *_unused)
  47 {
  48         unsigned mpidr, cpuid, clusterid, ob_cluster, ib_cluster;
  49
  50         /*
  51          * We now have a piece of stack borrowed from the init task's.
  52          * Let's also switch to init_mm right away to match it.
  53          */
  54         cpu_switch_mm(init_mm.pgd, &init_mm);
  55
  56         pr_debug("%s\n", __func__);
  57
  58         mpidr = read_mpidr();
  59         cpuid = MPIDR_AFFINITY_LEVEL(mpidr, 0);
  60         clusterid = MPIDR_AFFINITY_LEVEL(mpidr, 1);
  61         ob_cluster = clusterid;
  62         ib_cluster = clusterid ^ 1;
  63
  64         /*
  65          * Our state has been saved at this point.  Let's release our
  66          * inbound CPU.
  67          */
  68         mcpm_set_entry_vector(cpuid, ib_cluster, cpu_resume);
  69         sev();
  70
  71         /*
  72          * From this point, we must assume that our counterpart CPU might
  73          * have taken over in its parallel world already, as if execution
  74          * just returned from cpu_suspend().  It is therefore important to
  75          * be very careful not to make any change the other guy is not
  76          * expecting.  This is why we need stack isolation.
  77          *
  78          * Fancy under cover tasks could be performed here.  For now
  79          * we have none.
  80          */
  81
  82         /* Let's put ourself down. */
  83         mcpm_cpu_power_down();
  84
  85         /* should never get here */
  86         BUG();
  87 }
  88
  89 /*
  90  * Stack isolation.  To ensure 'current' remains valid, we just borrow
  91  * a slice of the init/idle task which should be fairly lightly used.
  92  * The borrowed area starts just above the thread_info structure located
  93  * at the very bottom of the stack, aligned to a cache line.
  94  */
  95 #define STACK_SIZE 256
  96 extern void call_with_stack(void (*fn)(void *), void *arg, void *sp);
  97 static int bL_switchpoint(unsigned long _arg)
  98 {
  99         unsigned int mpidr = read_mpidr();
 100         unsigned int cpuid = MPIDR_AFFINITY_LEVEL(mpidr, 0);
 101         unsigned int clusterid = MPIDR_AFFINITY_LEVEL(mpidr, 1);
 102         unsigned int cpu_index = cpuid + clusterid * MAX_CPUS_PER_CLUSTER;
 103         void *stack = &init_thread_info + 1;
 104         stack = PTR_ALIGN(stack, L1_CACHE_BYTES);
 105         stack += cpu_index * STACK_SIZE + STACK_SIZE;
 106         call_with_stack(bL_do_switch, (void *)_arg, stack);
 107         BUG();
 108 }
 109
 110 /*
 111  * Generic switcher interface
 112  */
 113
 114 /*
 115  * bL_switch_to - Switch to a specific cluster for the current CPU
 116  * @new_cluster_id: the ID of the cluster to switch to.
 117  *
 118  * This function must be called on the CPU to be switched.
 119  * Returns 0 on success, else a negative status code.
 120  */
 121 static int bL_switch_to(unsigned int new_cluster_id)
 122 {
 123         unsigned int mpidr, cpuid, clusterid, ob_cluster, ib_cluster, this_cpu;
 124         int ret;
 125
 126         mpidr = read_mpidr();
 127         cpuid = MPIDR_AFFINITY_LEVEL(mpidr, 0);
 128         clusterid = MPIDR_AFFINITY_LEVEL(mpidr, 1);
 129         ob_cluster = clusterid;
 130         ib_cluster = clusterid ^ 1;
 131
 132         if (new_cluster_id == clusterid)
 133                 return 0;
 134
 135         pr_debug("before switch: CPU %d in cluster %d\n", cpuid, clusterid);
 136
 137         /* Close the gate for our entry vectors */
 138         mcpm_set_entry_vector(cpuid, ob_cluster, NULL);
 139         mcpm_set_entry_vector(cpuid, ib_cluster, NULL);
 140
 141         /*
 142          * Let's wake up the inbound CPU now in case it requires some delay
 143          * to come online, but leave it gated in our entry vector code.
 144          */
 145         ret = mcpm_cpu_power_up(cpuid, ib_cluster);
 146         if (ret) {
 147                 pr_err("%s: mcpm_cpu_power_up() returned %d\n", __func__, ret);
 148                 return ret;
 149         }
 150
 151         /*
 152          * From this point we are entering the switch critical zone
 153          * and can't take any interrupts anymore.
 154          */
 155         local_irq_disable();
 156         local_fiq_disable();
 157
 158         this_cpu = smp_processor_id();
 159
 160         /* redirect GIC's SGIs to our counterpart */
 161         gic_migrate_target(cpuid + ib_cluster*4);
 162
 163         /*
 164          * Raise a SGI on the inbound CPU to make sure it doesn't stall
 165          * in a possible WFI, such as in mcpm_power_down().
 166          */
 167         arch_send_wakeup_ipi_mask(cpumask_of(this_cpu));
 168
 169         ret = cpu_pm_enter();
 170
 171         /* we can not tolerate errors at this point */
 172         if (ret)
 173                 panic("%s: cpu_pm_enter() returned %d\n", __func__, ret);
 174
 175         /* Flip the cluster in the CPU logical map for this CPU. */
 176         cpu_logical_map(this_cpu) ^= (1 << 8);
 177
 178         /* Let's do the actual CPU switch. */
 179         ret = cpu_suspend(0, bL_switchpoint);
 180         if (ret > 0)
 181                 panic("%s: cpu_suspend() returned %d\n", __func__, ret);
 182
 183         /* We are executing on the inbound CPU at this point */
 184         mpidr = read_mpidr();
 185         cpuid = MPIDR_AFFINITY_LEVEL(mpidr, 0);
 186         clusterid = MPIDR_AFFINITY_LEVEL(mpidr, 1);
 187         pr_debug("after switch: CPU %d in cluster %d\n", cpuid, clusterid);
 188         BUG_ON(clusterid != ib_cluster);
 189
 190         mcpm_cpu_powered_up();
 191
 192         ret = cpu_pm_exit();
 193
 194         local_fiq_enable();
 195         local_irq_enable();
 196
 197         if (ret)
 198                 pr_err("%s exiting with error %d\n", __func__, ret);
 199         return ret;
 200 }
 201
 202 struct switch_args {
 203         unsigned int cluster;
 204         struct work_struct work;
 205 };
 206
 207 static void __bL_switch_to(struct work_struct *work)
 208 {
 209         struct switch_args *args = container_of(work, struct switch_args, work);
 210         bL_switch_to(args->cluster);
 211 }
 212
 213 /*
 214  * bL_switch_request - Switch to a specific cluster for the given CPU
 215  *
 216  * @cpu: the CPU to switch
 217  * @new_cluster_id: the ID of the cluster to switch to.
 218  *
 219  * This function causes a cluster switch on the given CPU.  If the given
 220  * CPU is the same as the calling CPU then the switch happens right away.
 221  * Otherwise the request is put on a work queue to be scheduled on the
 222  * remote CPU.
 223  */
 224 void bL_switch_request(unsigned int cpu, unsigned int new_cluster_id)
 225 {
 226         unsigned int this_cpu = get_cpu();
 227         struct switch_args args;
 228
 229         if (cpu == this_cpu) {
 230                 bL_switch_to(new_cluster_id);
 231                 put_cpu();
 232                 return;
 233         }
 234         put_cpu();
 235
 236         args.cluster = new_cluster_id;
 237         INIT_WORK_ONSTACK(&args.work, __bL_switch_to);
 238         schedule_work_on(cpu, &args.work);
 239         flush_work(&args.work);
 240 }
 241 EXPORT_SYMBOL_GPL(bL_switch_request);