treewide: remove redundant IS_ERR() before error code check

[linux/fpc-iii.git] / arch / mips / kernel / pm-cps.c

// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Copyright (C) 2014 Imagination Technologies
 * Author: Paul Burton <paul.burton@mips.com>
 */

#include <linux/cpuhotplug.h>
#include <linux/init.h>
#include <linux/percpu.h>
#include <linux/slab.h>
#include <linux/suspend.h>

#include <asm/asm-offsets.h>
#include <asm/cacheflush.h>
#include <asm/cacheops.h>
#include <asm/idle.h>
#include <asm/mips-cps.h>
#include <asm/mipsmtregs.h>
#include <asm/pm.h>
#include <asm/pm-cps.h>
#include <asm/smp-cps.h>
#include <asm/uasm.h>

/*
 * cps_nc_entry_fn - type of a generated non-coherent state entry function
 * @online: the count of online coupled VPEs
 * @nc_ready_count: pointer to a non-coherent mapping of the core ready_count
 *
 * The code entering & exiting non-coherent states is generated at runtime
 * using uasm, in order to ensure that the compiler cannot insert a stray
 * memory access at an unfortunate time and to allow the generation of optimal
 * core-specific code particularly for cache routines. If coupled_coherence
 * is non-zero and this is the entry function for the CPS_PM_NC_WAIT state,
 * returns the number of VPEs that were in the wait state at the point this
 * VPE left it. Returns garbage if coupled_coherence is zero or this is not
 * the entry function for CPS_PM_NC_WAIT.
 */
typedef unsigned (*cps_nc_entry_fn)(unsigned online, u32 *nc_ready_count);

/*
 * The entry point of the generated non-coherent idle state entry/exit
 * functions. Actually per-core rather than per-CPU.
 */
static DEFINE_PER_CPU_READ_MOSTLY(cps_nc_entry_fn[CPS_PM_STATE_COUNT],
                                  nc_asm_enter);

/* Bitmap indicating which states are supported by the system */
static DECLARE_BITMAP(state_support, CPS_PM_STATE_COUNT);

/*
 * Indicates the number of coupled VPEs ready to operate in a non-coherent
 * state. Actually per-core rather than per-CPU.
 */
static DEFINE_PER_CPU_ALIGNED(u32*, ready_count);

/* Indicates online CPUs coupled with the current CPU */
static DEFINE_PER_CPU_ALIGNED(cpumask_t, online_coupled);

/*
 * Used to synchronize entry to deep idle states. Actually per-core rather
 * than per-CPU.
 */
static DEFINE_PER_CPU_ALIGNED(atomic_t, pm_barrier);

/* Saved CPU state across the CPS_PM_POWER_GATED state */
DEFINE_PER_CPU_ALIGNED(struct mips_static_suspend_state, cps_cpu_state);

/* A somewhat arbitrary number of labels & relocs for uasm */
static struct uasm_label labels[32];
static struct uasm_reloc relocs[32];

enum mips_reg {
        zero, at, v0, v1, a0, a1, a2, a3,
        t0, t1, t2, t3, t4, t5, t6, t7,
        s0, s1, s2, s3, s4, s5, s6, s7,
        t8, t9, k0, k1, gp, sp, fp, ra,
};

bool cps_pm_support_state(enum cps_pm_state state)
{
        return test_bit(state, state_support);
}

static void coupled_barrier(atomic_t *a, unsigned online)
{
        /*
         * This function is effectively the same as
         * cpuidle_coupled_parallel_barrier, which can't be used here since
         * there's no cpuidle device.
         */

        if (!coupled_coherence)
                return;

        smp_mb__before_atomic();
        atomic_inc(a);

        while (atomic_read(a) < online)
                cpu_relax();

        if (atomic_inc_return(a) == online * 2) {
                atomic_set(a, 0);
                return;
        }

        while (atomic_read(a) > online)
                cpu_relax();
}

int cps_pm_enter_state(enum cps_pm_state state)
{
        unsigned cpu = smp_processor_id();
        unsigned core = cpu_core(&current_cpu_data);
        unsigned online, left;
        cpumask_t *coupled_mask = this_cpu_ptr(&online_coupled);
        u32 *core_ready_count, *nc_core_ready_count;
        void *nc_addr;
        cps_nc_entry_fn entry;
        struct core_boot_config *core_cfg;
        struct vpe_boot_config *vpe_cfg;

        /* Check that there is an entry function for this state */
        entry = per_cpu(nc_asm_enter, core)[state];
        if (!entry)
                return -EINVAL;

        /* Calculate which coupled CPUs (VPEs) are online */
#if defined(CONFIG_MIPS_MT) || defined(CONFIG_CPU_MIPSR6)
        if (cpu_online(cpu)) {
                cpumask_and(coupled_mask, cpu_online_mask,
                            &cpu_sibling_map[cpu]);
                online = cpumask_weight(coupled_mask);
                cpumask_clear_cpu(cpu, coupled_mask);
        } else
#endif
        {
                cpumask_clear(coupled_mask);
                online = 1;
        }

        /* Setup the VPE to run mips_cps_pm_restore when started again */
        if (IS_ENABLED(CONFIG_CPU_PM) && state == CPS_PM_POWER_GATED) {
                /* Power gating relies upon CPS SMP */
                if (!mips_cps_smp_in_use())
                        return -EINVAL;

                core_cfg = &mips_cps_core_bootcfg[core];
                vpe_cfg = &core_cfg->vpe_config[cpu_vpe_id(&current_cpu_data)];
                vpe_cfg->pc = (unsigned long)mips_cps_pm_restore;
                vpe_cfg->gp = (unsigned long)current_thread_info();
                vpe_cfg->sp = 0;
        }

        /* Indicate that this CPU might not be coherent */
        cpumask_clear_cpu(cpu, &cpu_coherent_mask);
        smp_mb__after_atomic();

        /* Create a non-coherent mapping of the core ready_count */
        core_ready_count = per_cpu(ready_count, core);
        nc_addr = kmap_noncoherent(virt_to_page(core_ready_count),
                                   (unsigned long)core_ready_count);
        nc_addr += ((unsigned long)core_ready_count & ~PAGE_MASK);
        nc_core_ready_count = nc_addr;

        /* Ensure ready_count is zero-initialised before the assembly runs */
        WRITE_ONCE(*nc_core_ready_count, 0);
        coupled_barrier(&per_cpu(pm_barrier, core), online);

        /* Run the generated entry code */
        left = entry(online, nc_core_ready_count);

        /* Remove the non-coherent mapping of ready_count */
        kunmap_noncoherent();

        /* Indicate that this CPU is definitely coherent */
        cpumask_set_cpu(cpu, &cpu_coherent_mask);

        /*
         * If this VPE is the first to leave the non-coherent wait state then
         * it needs to wake up any coupled VPEs still running their wait
         * instruction so that they return to cpuidle, which can then complete
         * coordination between the coupled VPEs & provide the governor with
         * a chance to reflect on the length of time the VPEs were in the
         * idle state.
         */
        if (coupled_coherence && (state == CPS_PM_NC_WAIT) && (left == online))
                arch_send_call_function_ipi_mask(coupled_mask);

        return 0;
}

static void cps_gen_cache_routine(u32 **pp, struct uasm_label **pl,
                                  struct uasm_reloc **pr,
                                  const struct cache_desc *cache,
                                  unsigned op, int lbl)
{
        unsigned cache_size = cache->ways << cache->waybit;
        unsigned i;
        const unsigned unroll_lines = 32;

        /* If the cache isn't present this function has it easy */
        if (cache->flags & MIPS_CACHE_NOT_PRESENT)
                return;

        /* Load base address */
        UASM_i_LA(pp, t0, (long)CKSEG0);

        /* Calculate end address */
        if (cache_size < 0x8000)
                uasm_i_addiu(pp, t1, t0, cache_size);
        else
                UASM_i_LA(pp, t1, (long)(CKSEG0 + cache_size));

        /* Start of cache op loop */
        uasm_build_label(pl, *pp, lbl);

        /* Generate the cache ops */
        for (i = 0; i < unroll_lines; i++) {
                if (cpu_has_mips_r6) {
                        uasm_i_cache(pp, op, 0, t0);
                        uasm_i_addiu(pp, t0, t0, cache->linesz);
                } else {
                        uasm_i_cache(pp, op, i * cache->linesz, t0);
                }
        }

        if (!cpu_has_mips_r6)
                /* Update the base address */
                uasm_i_addiu(pp, t0, t0, unroll_lines * cache->linesz);

        /* Loop if we haven't reached the end address yet */
        uasm_il_bne(pp, pr, t0, t1, lbl);
        uasm_i_nop(pp);
}

static int cps_gen_flush_fsb(u32 **pp, struct uasm_label **pl,
                             struct uasm_reloc **pr,
                             const struct cpuinfo_mips *cpu_info,
                             int lbl)
{
        unsigned i, fsb_size = 8;
        unsigned num_loads = (fsb_size * 3) / 2;
        unsigned line_stride = 2;
        unsigned line_size = cpu_info->dcache.linesz;
        unsigned perf_counter, perf_event;
        unsigned revision = cpu_info->processor_id & PRID_REV_MASK;

        /*
         * Determine whether this CPU requires an FSB flush, and if so which
         * performance counter/event reflect stalls due to a full FSB.
         */
        switch (__get_cpu_type(cpu_info->cputype)) {
        case CPU_INTERAPTIV:
                perf_counter = 1;
                perf_event = 51;
                break;

        case CPU_PROAPTIV:
                /* Newer proAptiv cores don't require this workaround */
                if (revision >= PRID_REV_ENCODE_332(1, 1, 0))
                        return 0;

                /* On older ones it's unavailable */
                return -1;

        default:
                /* Assume that the CPU does not need this workaround */
                return 0;
        }

        /*
         * Ensure that the fill/store buffer (FSB) is not holding the results
         * of a prefetch, since if it is then the CPC sequencer may become
         * stuck in the D3 (ClrBus) state whilst entering a low power state.
         */

        /* Preserve perf counter setup */
        uasm_i_mfc0(pp, t2, 25, (perf_counter * 2) + 0); /* PerfCtlN */
        uasm_i_mfc0(pp, t3, 25, (perf_counter * 2) + 1); /* PerfCntN */

        /* Setup perf counter to count FSB full pipeline stalls */
        uasm_i_addiu(pp, t0, zero, (perf_event << 5) | 0xf);
        uasm_i_mtc0(pp, t0, 25, (perf_counter * 2) + 0); /* PerfCtlN */
        uasm_i_ehb(pp);
        uasm_i_mtc0(pp, zero, 25, (perf_counter * 2) + 1); /* PerfCntN */
        uasm_i_ehb(pp);

        /* Base address for loads */
        UASM_i_LA(pp, t0, (long)CKSEG0);

        /* Start of clear loop */
        uasm_build_label(pl, *pp, lbl);

        /* Perform some loads to fill the FSB */
        for (i = 0; i < num_loads; i++)
                uasm_i_lw(pp, zero, i * line_size * line_stride, t0);

        /*
         * Invalidate the new D-cache entries so that the cache will need
         * refilling (via the FSB) if the loop is executed again.
         */
        for (i = 0; i < num_loads; i++) {
                uasm_i_cache(pp, Hit_Invalidate_D,
                             i * line_size * line_stride, t0);
                uasm_i_cache(pp, Hit_Writeback_Inv_SD,
                             i * line_size * line_stride, t0);
        }

        /* Barrier ensuring previous cache invalidates are complete */
        uasm_i_sync(pp, __SYNC_full);
        uasm_i_ehb(pp);

        /* Check whether the pipeline stalled due to the FSB being full */
        uasm_i_mfc0(pp, t1, 25, (perf_counter * 2) + 1); /* PerfCntN */

        /* Loop if it didn't */
        uasm_il_beqz(pp, pr, t1, lbl);
        uasm_i_nop(pp);

        /* Restore perf counter 1. The count may well now be wrong... */
        uasm_i_mtc0(pp, t2, 25, (perf_counter * 2) + 0); /* PerfCtlN */
        uasm_i_ehb(pp);
        uasm_i_mtc0(pp, t3, 25, (perf_counter * 2) + 1); /* PerfCntN */
        uasm_i_ehb(pp);

        return 0;
}

static void cps_gen_set_top_bit(u32 **pp, struct uasm_label **pl,
                                struct uasm_reloc **pr,
                                unsigned r_addr, int lbl)
{
        uasm_i_lui(pp, t0, uasm_rel_hi(0x80000000));
        uasm_build_label(pl, *pp, lbl);
        uasm_i_ll(pp, t1, 0, r_addr);
        uasm_i_or(pp, t1, t1, t0);
        uasm_i_sc(pp, t1, 0, r_addr);
        uasm_il_beqz(pp, pr, t1, lbl);
        uasm_i_nop(pp);
}

static void *cps_gen_entry_code(unsigned cpu, enum cps_pm_state state)
{
        struct uasm_label *l = labels;
        struct uasm_reloc *r = relocs;
        u32 *buf, *p;
        const unsigned r_online = a0;
        const unsigned r_nc_count = a1;
        const unsigned r_pcohctl = t7;
        const unsigned max_instrs = 256;
        unsigned cpc_cmd;
        int err;
        enum {
                lbl_incready = 1,
                lbl_poll_cont,
                lbl_secondary_hang,
                lbl_disable_coherence,
                lbl_flush_fsb,
                lbl_invicache,
                lbl_flushdcache,
                lbl_hang,
                lbl_set_cont,
                lbl_secondary_cont,
                lbl_decready,
        };

        /* Allocate a buffer to hold the generated code */
        p = buf = kcalloc(max_instrs, sizeof(u32), GFP_KERNEL);
        if (!buf)
                return NULL;

        /* Clear labels & relocs ready for (re)use */
        memset(labels, 0, sizeof(labels));
        memset(relocs, 0, sizeof(relocs));

        if (IS_ENABLED(CONFIG_CPU_PM) && state == CPS_PM_POWER_GATED) {
                /* Power gating relies upon CPS SMP */
                if (!mips_cps_smp_in_use())
                        goto out_err;

                /*
                 * Save CPU state. Note the non-standard calling convention
                 * with the return address placed in v0 to avoid clobbering
                 * the ra register before it is saved.
                 */
                UASM_i_LA(&p, t0, (long)mips_cps_pm_save);
                uasm_i_jalr(&p, v0, t0);
                uasm_i_nop(&p);
        }

        /*
         * Load addresses of required CM & CPC registers. This is done early
         * because they're needed in both the enable & disable coherence steps
         * but in the coupled case the enable step will only run on one VPE.
         */
        UASM_i_LA(&p, r_pcohctl, (long)addr_gcr_cl_coherence());

        if (coupled_coherence) {
                /* Increment ready_count */
                uasm_i_sync(&p, __SYNC_mb);
                uasm_build_label(&l, p, lbl_incready);
                uasm_i_ll(&p, t1, 0, r_nc_count);
                uasm_i_addiu(&p, t2, t1, 1);
                uasm_i_sc(&p, t2, 0, r_nc_count);
                uasm_il_beqz(&p, &r, t2, lbl_incready);
                uasm_i_addiu(&p, t1, t1, 1);

                /* Barrier ensuring all CPUs see the updated r_nc_count value */
                uasm_i_sync(&p, __SYNC_mb);

                /*
                 * If this is the last VPE to become ready for non-coherence
                 * then it should branch below.
                 */
                uasm_il_beq(&p, &r, t1, r_online, lbl_disable_coherence);
                uasm_i_nop(&p);

                if (state < CPS_PM_POWER_GATED) {
                        /*
                         * Otherwise this is not the last VPE to become ready
                         * for non-coherence. It needs to wait until coherence
                         * has been disabled before proceeding, which it will do
                         * by polling for the top bit of ready_count being set.
                         */
                        uasm_i_addiu(&p, t1, zero, -1);
                        uasm_build_label(&l, p, lbl_poll_cont);
                        uasm_i_lw(&p, t0, 0, r_nc_count);
                        uasm_il_bltz(&p, &r, t0, lbl_secondary_cont);
                        uasm_i_ehb(&p);
                        if (cpu_has_mipsmt)
                                uasm_i_yield(&p, zero, t1);
                        uasm_il_b(&p, &r, lbl_poll_cont);
                        uasm_i_nop(&p);
                } else {
                        /*
                         * The core will lose power & this VPE will not continue
                         * so it can simply halt here.
                         */
                        if (cpu_has_mipsmt) {
                                /* Halt the VPE via C0 tchalt register */
                                uasm_i_addiu(&p, t0, zero, TCHALT_H);
                                uasm_i_mtc0(&p, t0, 2, 4);
                        } else if (cpu_has_vp) {
                                /* Halt the VP via the CPC VP_STOP register */
                                unsigned int vpe_id;

                                vpe_id = cpu_vpe_id(&cpu_data[cpu]);
                                uasm_i_addiu(&p, t0, zero, 1 << vpe_id);
                                UASM_i_LA(&p, t1, (long)addr_cpc_cl_vp_stop());
                                uasm_i_sw(&p, t0, 0, t1);
                        } else {
                                BUG();
                        }
                        uasm_build_label(&l, p, lbl_secondary_hang);
                        uasm_il_b(&p, &r, lbl_secondary_hang);
                        uasm_i_nop(&p);
                }
        }

        /*
         * This is the point of no return - this VPE will now proceed to
         * disable coherence. At this point we *must* be sure that no other
         * VPE within the core will interfere with the L1 dcache.
         */
        uasm_build_label(&l, p, lbl_disable_coherence);

        /* Invalidate the L1 icache */
        cps_gen_cache_routine(&p, &l, &r, &cpu_data[cpu].icache,
                              Index_Invalidate_I, lbl_invicache);

        /* Writeback & invalidate the L1 dcache */
        cps_gen_cache_routine(&p, &l, &r, &cpu_data[cpu].dcache,
                              Index_Writeback_Inv_D, lbl_flushdcache);

        /* Barrier ensuring previous cache invalidates are complete */
        uasm_i_sync(&p, __SYNC_full);
        uasm_i_ehb(&p);

        if (mips_cm_revision() < CM_REV_CM3) {
                /*
                * Disable all but self interventions. The load from COHCTL is
                * defined by the interAptiv & proAptiv SUMs as ensuring that the
                *  operation resulting from the preceding store is complete.
                */
                uasm_i_addiu(&p, t0, zero, 1 << cpu_core(&cpu_data[cpu]));
                uasm_i_sw(&p, t0, 0, r_pcohctl);
                uasm_i_lw(&p, t0, 0, r_pcohctl);

                /* Barrier to ensure write to coherence control is complete */
                uasm_i_sync(&p, __SYNC_full);
                uasm_i_ehb(&p);
        }

        /* Disable coherence */
        uasm_i_sw(&p, zero, 0, r_pcohctl);
        uasm_i_lw(&p, t0, 0, r_pcohctl);

        if (state >= CPS_PM_CLOCK_GATED) {
                err = cps_gen_flush_fsb(&p, &l, &r, &cpu_data[cpu],
                                        lbl_flush_fsb);
                if (err)
                        goto out_err;

                /* Determine the CPC command to issue */
                switch (state) {
                case CPS_PM_CLOCK_GATED:
                        cpc_cmd = CPC_Cx_CMD_CLOCKOFF;
                        break;
                case CPS_PM_POWER_GATED:
                        cpc_cmd = CPC_Cx_CMD_PWRDOWN;
                        break;
                default:
                        BUG();
                        goto out_err;
                }

                /* Issue the CPC command */
                UASM_i_LA(&p, t0, (long)addr_cpc_cl_cmd());
                uasm_i_addiu(&p, t1, zero, cpc_cmd);
                uasm_i_sw(&p, t1, 0, t0);

                if (state == CPS_PM_POWER_GATED) {
                        /* If anything goes wrong just hang */
                        uasm_build_label(&l, p, lbl_hang);
                        uasm_il_b(&p, &r, lbl_hang);
                        uasm_i_nop(&p);

                        /*
                         * There's no point generating more code, the core is
                         * powered down & if powered back up will run from the
                         * reset vector not from here.
                         */
                        goto gen_done;
                }

                /* Barrier to ensure write to CPC command is complete */
                uasm_i_sync(&p, __SYNC_full);
                uasm_i_ehb(&p);
        }

        if (state == CPS_PM_NC_WAIT) {
                /*
                 * At this point it is safe for all VPEs to proceed with
                 * execution. This VPE will set the top bit of ready_count
                 * to indicate to the other VPEs that they may continue.
                 */
                if (coupled_coherence)
                        cps_gen_set_top_bit(&p, &l, &r, r_nc_count,
                                            lbl_set_cont);

                /*
                 * VPEs which did not disable coherence will continue
                 * executing, after coherence has been disabled, from this
                 * point.
                 */
                uasm_build_label(&l, p, lbl_secondary_cont);

                /* Now perform our wait */
                uasm_i_wait(&p, 0);
        }

        /*
         * Re-enable coherence. Note that for CPS_PM_NC_WAIT all coupled VPEs
         * will run this. The first will actually re-enable coherence & the
         * rest will just be performing a rather unusual nop.
         */
        uasm_i_addiu(&p, t0, zero, mips_cm_revision() < CM_REV_CM3
                                ? CM_GCR_Cx_COHERENCE_COHDOMAINEN
                                : CM3_GCR_Cx_COHERENCE_COHEN);

        uasm_i_sw(&p, t0, 0, r_pcohctl);
        uasm_i_lw(&p, t0, 0, r_pcohctl);

        /* Barrier to ensure write to coherence control is complete */
        uasm_i_sync(&p, __SYNC_full);
        uasm_i_ehb(&p);

        if (coupled_coherence && (state == CPS_PM_NC_WAIT)) {
                /* Decrement ready_count */
                uasm_build_label(&l, p, lbl_decready);
                uasm_i_sync(&p, __SYNC_mb);
                uasm_i_ll(&p, t1, 0, r_nc_count);
                uasm_i_addiu(&p, t2, t1, -1);
                uasm_i_sc(&p, t2, 0, r_nc_count);
                uasm_il_beqz(&p, &r, t2, lbl_decready);
                uasm_i_andi(&p, v0, t1, (1 << fls(smp_num_siblings)) - 1);

                /* Barrier ensuring all CPUs see the updated r_nc_count value */
                uasm_i_sync(&p, __SYNC_mb);
        }

        if (coupled_coherence && (state == CPS_PM_CLOCK_GATED)) {
                /*
                 * At this point it is safe for all VPEs to proceed with
                 * execution. This VPE will set the top bit of ready_count
                 * to indicate to the other VPEs that they may continue.
                 */
                cps_gen_set_top_bit(&p, &l, &r, r_nc_count, lbl_set_cont);

                /*
                 * This core will be reliant upon another core sending a
                 * power-up command to the CPC in order to resume operation.
                 * Thus an arbitrary VPE can't trigger the core leaving the
                 * idle state and the one that disables coherence might as well
                 * be the one to re-enable it. The rest will continue from here
                 * after that has been done.
                 */
                uasm_build_label(&l, p, lbl_secondary_cont);

                /* Barrier ensuring all CPUs see the updated r_nc_count value */
                uasm_i_sync(&p, __SYNC_mb);
        }

        /* The core is coherent, time to return to C code */
        uasm_i_jr(&p, ra);
        uasm_i_nop(&p);

gen_done:
        /* Ensure the code didn't exceed the resources allocated for it */
        BUG_ON((p - buf) > max_instrs);
        BUG_ON((l - labels) > ARRAY_SIZE(labels));
        BUG_ON((r - relocs) > ARRAY_SIZE(relocs));

        /* Patch branch offsets */
        uasm_resolve_relocs(relocs, labels);

        /* Flush the icache */
        local_flush_icache_range((unsigned long)buf, (unsigned long)p);

        return buf;
out_err:
        kfree(buf);
        return NULL;
}

static int cps_pm_online_cpu(unsigned int cpu)
{
        enum cps_pm_state state;
        unsigned core = cpu_core(&cpu_data[cpu]);
        void *entry_fn, *core_rc;

        for (state = CPS_PM_NC_WAIT; state < CPS_PM_STATE_COUNT; state++) {
                if (per_cpu(nc_asm_enter, core)[state])
                        continue;
                if (!test_bit(state, state_support))
                        continue;

                entry_fn = cps_gen_entry_code(cpu, state);
                if (!entry_fn) {
                        pr_err("Failed to generate core %u state %u entry\n",
                               core, state);
                        clear_bit(state, state_support);
                }

                per_cpu(nc_asm_enter, core)[state] = entry_fn;
        }

        if (!per_cpu(ready_count, core)) {
                core_rc = kmalloc(sizeof(u32), GFP_KERNEL);
                if (!core_rc) {
                        pr_err("Failed allocate core %u ready_count\n", core);
                        return -ENOMEM;
                }
                per_cpu(ready_count, core) = core_rc;
        }

        return 0;
}

static int cps_pm_power_notifier(struct notifier_block *this,
                                 unsigned long event, void *ptr)
{
        unsigned int stat;

        switch (event) {
        case PM_SUSPEND_PREPARE:
                stat = read_cpc_cl_stat_conf();
                /*
                 * If we're attempting to suspend the system and power down all
                 * of the cores, the JTAG detect bit indicates that the CPC will
                 * instead put the cores into clock-off state. In this state
                 * a connected debugger can cause the CPU to attempt
                 * interactions with the powered down system. At best this will
                 * fail. At worst, it can hang the NoC, requiring a hard reset.
                 * To avoid this, just block system suspend if a JTAG probe
                 * is detected.
                 */
                if (stat & CPC_Cx_STAT_CONF_EJTAG_PROBE) {
                        pr_warn("JTAG probe is connected - abort suspend\n");
                        return NOTIFY_BAD;
                }
                return NOTIFY_DONE;
        default:
                return NOTIFY_DONE;
        }
}

static int __init cps_pm_init(void)
{
        /* A CM is required for all non-coherent states */
        if (!mips_cm_present()) {
                pr_warn("pm-cps: no CM, non-coherent states unavailable\n");
                return 0;
        }

        /*
         * If interrupts were enabled whilst running a wait instruction on a
         * non-coherent core then the VPE may end up processing interrupts
         * whilst non-coherent. That would be bad.
         */
        if (cpu_wait == r4k_wait_irqoff)
                set_bit(CPS_PM_NC_WAIT, state_support);
        else
                pr_warn("pm-cps: non-coherent wait unavailable\n");

        /* Detect whether a CPC is present */
        if (mips_cpc_present()) {
                /* Detect whether clock gating is implemented */
                if (read_cpc_cl_stat_conf() & CPC_Cx_STAT_CONF_CLKGAT_IMPL)
                        set_bit(CPS_PM_CLOCK_GATED, state_support);
                else
                        pr_warn("pm-cps: CPC does not support clock gating\n");

                /* Power gating is available with CPS SMP & any CPC */
                if (mips_cps_smp_in_use())
                        set_bit(CPS_PM_POWER_GATED, state_support);
                else
                        pr_warn("pm-cps: CPS SMP not in use, power gating unavailable\n");
        } else {
                pr_warn("pm-cps: no CPC, clock & power gating unavailable\n");
        }

        pm_notifier(cps_pm_power_notifier, 0);

        return cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "mips/cps_pm:online",
                                 cps_pm_online_cpu, NULL);
}
arch_initcall(cps_pm_init);