MIPS: smp-cps: hotplug support

This patch adds support for offlining CPUs via hotplug when using the
CONFIG_MIPS_CPS SMP implementation. When a CPU is offlined one of 2
things will happen:

  - If the CPU is part of a core which implements the MT ASE and there
    is at least one other VPE online within that core then the VPE will
    be halted by settings its TCHalt bit.

  - Otherwise if supported the core will be powered down via the CPC.

  - Otherwise the CPU will hang by executing an infinite loop.

Bringing CPUs back online is then a process of either clearing the
appropriate VPEs TCHalt bit or powering up the appropriate core via the
CPC. Throughout the process the struct core_boot_config vpe_mask field
must be maintained such that mips_cps_boot_vpes will start & stop the
correct VPEs.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>

diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
index c79e6a4..860a1e9 100644 (file)
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -2059,9 +2059,11 @@ config MIPS_CPS
        depends on SYS_SUPPORTS_MIPS_CPS
        select MIPS_CM
        select MIPS_CPC
+       select MIPS_CPS_PM if HOTPLUG_CPU
        select MIPS_GIC_IPI
        select SMP
        select SYNC_R4K if (CEVT_R4K || CSRC_R4K)
+       select SYS_SUPPORTS_HOTPLUG_CPU
        select SYS_SUPPORTS_SMP
        select WEAK_ORDERING
        help

diff --git a/arch/mips/kernel/smp-cps.c b/arch/mips/kernel/smp-cps.c
index b519c85..3c30891 100644 (file)
--- a/arch/mips/kernel/smp-cps.c
+++ b/arch/mips/kernel/smp-cps.c
@@ -20,6 +20,7 @@
 #include <asm/mips-cpc.h>
 #include <asm/mips_mt.h>
 #include <asm/mipsregs.h>
+#include <asm/pm-cps.h>
 #include <asm/smp-cps.h>
 #include <asm/time.h>
 #include <asm/uasm.h>
@@ -194,10 +195,12 @@ static void cps_boot_secondary(int cpu, struct task_struct *idle)
 
        atomic_or(1 << cpu_vpe_id(&cpu_data[cpu]), &core_cfg->vpe_mask);
 
+       preempt_disable();
+
        if (!test_bit(core, core_power)) {
                /* Boot a VPE on a powered down core */
                boot_core(core);
-               return;
+               goto out;
        }
 
        if (core != current_cpu_data.core) {
@@ -214,13 +217,15 @@ static void cps_boot_secondary(int cpu, struct task_struct *idle)
                                               NULL, 1);
                if (err)
                        panic("Failed to call remote CPU\n");
-               return;
+               goto out;
        }
 
        BUG_ON(!cpu_has_mipsmt);
 
        /* Boot a VPE on this core */
        mips_cps_boot_vpes();
+out:
+       preempt_enable();
 }
 
 static void cps_init_secondary(void)
@@ -250,6 +255,148 @@ static void cps_cpus_done(void)
 {
 }
 
+#ifdef CONFIG_HOTPLUG_CPU
+
+static int cps_cpu_disable(void)
+{
+       unsigned cpu = smp_processor_id();
+       struct core_boot_config *core_cfg;
+
+       if (!cpu)
+               return -EBUSY;
+
+       if (!cps_pm_support_state(CPS_PM_POWER_GATED))
+               return -EINVAL;
+
+       core_cfg = &mips_cps_core_bootcfg[current_cpu_data.core];
+       atomic_sub(1 << cpu_vpe_id(&current_cpu_data), &core_cfg->vpe_mask);
+       smp_mb__after_atomic_dec();
+       set_cpu_online(cpu, false);
+       cpu_clear(cpu, cpu_callin_map);
+
+       return 0;
+}
+
+static DECLARE_COMPLETION(cpu_death_chosen);
+static unsigned cpu_death_sibling;
+static enum {
+       CPU_DEATH_HALT,
+       CPU_DEATH_POWER,
+} cpu_death;
+
+void play_dead(void)
+{
+       unsigned cpu, core;
+
+       local_irq_disable();
+       idle_task_exit();
+       cpu = smp_processor_id();
+       cpu_death = CPU_DEATH_POWER;
+
+       if (cpu_has_mipsmt) {
+               core = cpu_data[cpu].core;
+
+               /* Look for another online VPE within the core */
+               for_each_online_cpu(cpu_death_sibling) {
+                       if (cpu_data[cpu_death_sibling].core != core)
+                               continue;
+
+                       /*
+                        * There is an online VPE within the core. Just halt
+                        * this TC and leave the core alone.
+                        */
+                       cpu_death = CPU_DEATH_HALT;
+                       break;
+               }
+       }
+
+       /* This CPU has chosen its way out */
+       complete(&cpu_death_chosen);
+
+       if (cpu_death == CPU_DEATH_HALT) {
+               /* Halt this TC */
+               write_c0_tchalt(TCHALT_H);
+               instruction_hazard();
+       } else {
+               /* Power down the core */
+               cps_pm_enter_state(CPS_PM_POWER_GATED);
+       }
+
+       /* This should never be reached */
+       panic("Failed to offline CPU %u", cpu);
+}
+
+static void wait_for_sibling_halt(void *ptr_cpu)
+{
+       unsigned cpu = (unsigned)ptr_cpu;
+       unsigned vpe_id = cpu_data[cpu].vpe_id;
+       unsigned halted;
+       unsigned long flags;
+
+       do {
+               local_irq_save(flags);
+               settc(vpe_id);
+               halted = read_tc_c0_tchalt();
+               local_irq_restore(flags);
+       } while (!(halted & TCHALT_H));
+}
+
+static void cps_cpu_die(unsigned int cpu)
+{
+       unsigned core = cpu_data[cpu].core;
+       unsigned stat;
+       int err;
+
+       /* Wait for the cpu to choose its way out */
+       if (!wait_for_completion_timeout(&cpu_death_chosen,
+                                        msecs_to_jiffies(5000))) {
+               pr_err("CPU%u: didn't offline\n", cpu);
+               return;
+       }
+
+       /*
+        * Now wait for the CPU to actually offline. Without doing this that
+        * offlining may race with one or more of:
+        *
+        *   - Onlining the CPU again.
+        *   - Powering down the core if another VPE within it is offlined.
+        *   - A sibling VPE entering a non-coherent state.
+        *
+        * In the non-MT halt case (ie. infinite loop) the CPU is doing nothing
+        * with which we could race, so do nothing.
+        */
+       if (cpu_death == CPU_DEATH_POWER) {
+               /*
+                * Wait for the core to enter a powered down or clock gated
+                * state, the latter happening when a JTAG probe is connected
+                * in which case the CPC will refuse to power down the core.
+                */
+               do {
+                       mips_cpc_lock_other(core);
+                       stat = read_cpc_co_stat_conf();
+                       stat &= CPC_Cx_STAT_CONF_SEQSTATE_MSK;
+                       mips_cpc_unlock_other();
+               } while (stat != CPC_Cx_STAT_CONF_SEQSTATE_D0 &&
+                        stat != CPC_Cx_STAT_CONF_SEQSTATE_D2 &&
+                        stat != CPC_Cx_STAT_CONF_SEQSTATE_U2);
+
+               /* Indicate the core is powered off */
+               bitmap_clear(core_power, core, 1);
+       } else if (cpu_has_mipsmt) {
+               /*
+                * Have a CPU with access to the offlined CPUs registers wait
+                * for its TC to halt.
+                */
+               err = smp_call_function_single(cpu_death_sibling,
+                                              wait_for_sibling_halt,
+                                              (void *)cpu, 1);
+               if (err)
+                       panic("Failed to call remote sibling CPU\n");
+       }
+}
+
+#endif /* CONFIG_HOTPLUG_CPU */
+
 static struct plat_smp_ops cps_smp_ops = {
        .smp_setup              = cps_smp_setup,
        .prepare_cpus           = cps_prepare_cpus,
@@ -259,6 +406,10 @@ static struct plat_smp_ops cps_smp_ops = {
        .send_ipi_single        = gic_send_ipi_single,
        .send_ipi_mask          = gic_send_ipi_mask,
        .cpus_done              = cps_cpus_done,
+#ifdef CONFIG_HOTPLUG_CPU
+       .cpu_disable            = cps_cpu_disable,
+       .cpu_die                = cps_cpu_die,
+#endif
 };
 
 bool mips_cps_smp_in_use(void)