// SPDX-License-Identifier: GPL-2.0
/*
 *  cpuidle-pseries - idle state cpuidle driver.
 *  Adapted from drivers/idle/intel_idle.c and
 *  drivers/acpi/processor_idle.c
 *
 */

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/moduleparam.h>
#include <linux/cpuidle.h>
#include <linux/cpu.h>
#include <linux/notifier.h>

#include <asm/paca.h>
#include <asm/reg.h>
#include <asm/machdep.h>
#include <asm/firmware.h>
#include <asm/runlatch.h>
#include <asm/idle.h>
#include <asm/plpar_wrappers.h>
#include <asm/rtas.h>

static struct cpuidle_driver pseries_idle_driver = {
        .name             = "pseries_idle",
        .owner            = THIS_MODULE,
};

static int max_idle_state __read_mostly;
static struct cpuidle_state *cpuidle_state_table __read_mostly;
static u64 snooze_timeout __read_mostly;
static bool snooze_timeout_en __read_mostly;

static int snooze_loop(struct cpuidle_device *dev,
                        struct cpuidle_driver *drv,
                        int index)
{
        u64 snooze_exit_time;

        set_thread_flag(TIF_POLLING_NRFLAG);

        pseries_idle_prolog();
        local_irq_enable();
        snooze_exit_time = get_tb() + snooze_timeout;

        while (!need_resched()) {
                HMT_low();
                HMT_very_low();
                if (likely(snooze_timeout_en) && get_tb() > snooze_exit_time) {
                        /*
                         * Task has not woken up but we are exiting the polling
                         * loop anyway. Require a barrier after polling is
                         * cleared to order subsequent test of need_resched().
                         */
                        clear_thread_flag(TIF_POLLING_NRFLAG);
                        smp_mb();
                        break;
                }
        }

        HMT_medium();
        clear_thread_flag(TIF_POLLING_NRFLAG);

        local_irq_disable();

        pseries_idle_epilog();

        return index;
}

static void check_and_cede_processor(void)
{
        /*
         * Ensure our interrupt state is properly tracked,
         * also checks if no interrupt has occurred while we
         * were soft-disabled
         */
        if (prep_irq_for_idle()) {
                cede_processor();
#ifdef CONFIG_TRACE_IRQFLAGS
                /* Ensure that H_CEDE returns with IRQs on */
                if (WARN_ON(!(mfmsr() & MSR_EE)))
                        __hard_irq_enable();
#endif
        }
}

/*
 * XCEDE: Extended CEDE states discovered through the
 *        "ibm,get-systems-parameter" RTAS call with the token
 *        CEDE_LATENCY_TOKEN
 */

/*
 * Section 7.3.16 System Parameters Option of PAPR version 2.8.1 has a
 * table with all the parameters to ibm,get-system-parameters.
 * CEDE_LATENCY_TOKEN corresponds to the token value for Cede Latency
 * Settings Information.
 */
#define CEDE_LATENCY_TOKEN      45

/*
 * If the platform supports the cede latency settings information system
 * parameter it must provide the following information in the NULL terminated
 * parameter string:
 *
 * a. The first byte is the length “N” of each cede latency setting record minus
 *    one (zero indicates a length of 1 byte).
 *
 * b. For each supported cede latency setting a cede latency setting record
 *    consisting of the first “N” bytes as per the following table.
 *
 *    -----------------------------
 *    | Field           | Field   |
 *    | Name            | Length  |
 *    -----------------------------
 *    | Cede Latency    | 1 Byte  |
 *    | Specifier Value |         |
 *    -----------------------------
 *    | Maximum wakeup  |         |
 *    | latency in      | 8 Bytes |
 *    | tb-ticks        |         |
 *    -----------------------------
 *    | Responsive to   |         |
 *    | external        | 1 Byte  |
 *    | interrupts      |         |
 *    -----------------------------
 *
 * This version has cede latency record size = 10.
 *
 * The structure xcede_latency_payload represents a) and b) with
 * xcede_latency_record representing the table in b).
 *
 * xcede_latency_parameter is what gets returned by
 * ibm,get-systems-parameter RTAS call when made with
 * CEDE_LATENCY_TOKEN.
 *
 * These structures are only used to represent the data obtained by the RTAS
 * call. The data is in big-endian.
 */
struct xcede_latency_record {
        u8      hint;
        __be64  latency_ticks;
        u8      wake_on_irqs;
} __packed;

// Make space for 16 records, which "should be enough".
struct xcede_latency_payload {
        u8     record_size;
        struct xcede_latency_record records[16];
} __packed;

struct xcede_latency_parameter {
        __be16  payload_size;
        struct xcede_latency_payload payload;
        u8 null_char;
} __packed;

static unsigned int nr_xcede_records;
static struct xcede_latency_parameter xcede_latency_parameter __initdata;

static int __init parse_cede_parameters(void)
{
        struct xcede_latency_payload *payload;
        u32 total_xcede_records_size;
        u8 xcede_record_size;
        u16 payload_size;
        int ret, i;

        ret = rtas_call(rtas_token("ibm,get-system-parameter"), 3, 1,
                        NULL, CEDE_LATENCY_TOKEN, __pa(&xcede_latency_parameter),
                        sizeof(xcede_latency_parameter));
        if (ret) {
                pr_err("xcede: Error parsing CEDE_LATENCY_TOKEN\n");
                return ret;
        }

        payload_size = be16_to_cpu(xcede_latency_parameter.payload_size);
        payload = &xcede_latency_parameter.payload;

        xcede_record_size = payload->record_size + 1;

        if (xcede_record_size != sizeof(struct xcede_latency_record)) {
                pr_err("xcede: Expected record-size %lu. Observed size %u.\n",
                       sizeof(struct xcede_latency_record), xcede_record_size);
                return -EINVAL;
        }

        pr_info("xcede: xcede_record_size = %d\n", xcede_record_size);

        /*
         * Since the payload_size includes the last NULL byte and the
         * xcede_record_size, the remaining bytes correspond to array of all
         * cede_latency settings.
         */
        total_xcede_records_size = payload_size - 2;
        nr_xcede_records = total_xcede_records_size / xcede_record_size;

        for (i = 0; i < nr_xcede_records; i++) {
                struct xcede_latency_record *record = &payload->records[i];
                u64 latency_ticks = be64_to_cpu(record->latency_ticks);
                u8 wake_on_irqs = record->wake_on_irqs;
                u8 hint = record->hint;

                pr_info("xcede: Record %d : hint = %u, latency = 0x%llx tb ticks, Wake-on-irq = %u\n",
                        i, hint, latency_ticks, wake_on_irqs);
        }

        return 0;
}

#define NR_DEDICATED_STATES     2 /* snooze, CEDE */
static u8 cede_latency_hint[NR_DEDICATED_STATES];

static int dedicated_cede_loop(struct cpuidle_device *dev,
                                struct cpuidle_driver *drv,
                                int index)
{
        u8 old_latency_hint;

        pseries_idle_prolog();
        get_lppaca()->donate_dedicated_cpu = 1;
        old_latency_hint = get_lppaca()->cede_latency_hint;
        get_lppaca()->cede_latency_hint = cede_latency_hint[index];

        HMT_medium();
        check_and_cede_processor();

        local_irq_disable();
        get_lppaca()->donate_dedicated_cpu = 0;
        get_lppaca()->cede_latency_hint = old_latency_hint;

        pseries_idle_epilog();

        return index;
}

static int shared_cede_loop(struct cpuidle_device *dev,
                        struct cpuidle_driver *drv,
                        int index)
{

        pseries_idle_prolog();

        /*
         * Yield the processor to the hypervisor.  We return if
         * an external interrupt occurs (which are driven prior
         * to returning here) or if a prod occurs from another
         * processor. When returning here, external interrupts
         * are enabled.
         */
        check_and_cede_processor();

        local_irq_disable();
        pseries_idle_epilog();

        return index;
}

/*
 * States for dedicated partition case.
 */
static struct cpuidle_state dedicated_states[NR_DEDICATED_STATES] = {
        { /* Snooze */
                .name = "snooze",
                .desc = "snooze",
                .exit_latency = 0,
                .target_residency = 0,
                .enter = &snooze_loop },
        { /* CEDE */
                .name = "CEDE",
                .desc = "CEDE",
                .exit_latency = 10,
                .target_residency = 100,
                .enter = &dedicated_cede_loop },
};

/*
 * States for shared partition case.
 */
static struct cpuidle_state shared_states[] = {
        { /* Snooze */
                .name = "snooze",
                .desc = "snooze",
                .exit_latency = 0,
                .target_residency = 0,
                .enter = &snooze_loop },
        { /* Shared Cede */
                .name = "Shared Cede",
                .desc = "Shared Cede",
                .exit_latency = 10,
                .target_residency = 100,
                .enter = &shared_cede_loop },
};

static int pseries_cpuidle_cpu_online(unsigned int cpu)
{
        struct cpuidle_device *dev = per_cpu(cpuidle_devices, cpu);

        if (dev && cpuidle_get_driver()) {
                cpuidle_pause_and_lock();
                cpuidle_enable_device(dev);
                cpuidle_resume_and_unlock();
        }
        return 0;
}

static int pseries_cpuidle_cpu_dead(unsigned int cpu)
{
        struct cpuidle_device *dev = per_cpu(cpuidle_devices, cpu);

        if (dev && cpuidle_get_driver()) {
                cpuidle_pause_and_lock();
                cpuidle_disable_device(dev);
                cpuidle_resume_and_unlock();
        }
        return 0;
}

/*
 * pseries_cpuidle_driver_init()
 */
static int pseries_cpuidle_driver_init(void)
{
        int idle_state;
        struct cpuidle_driver *drv = &pseries_idle_driver;

        drv->state_count = 0;

        for (idle_state = 0; idle_state < max_idle_state; ++idle_state) {
                /* Is the state not enabled? */
                if (cpuidle_state_table[idle_state].enter == NULL)
                        continue;

                drv->states[drv->state_count] = /* structure copy */
                        cpuidle_state_table[idle_state];

                drv->state_count += 1;
        }

        return 0;
}

static void __init fixup_cede0_latency(void)
{
        struct xcede_latency_payload *payload;
        u64 min_xcede_latency_us = UINT_MAX;
        int i;

        if (parse_cede_parameters())
                return;

        pr_info("cpuidle: Skipping the %d Extended CEDE idle states\n",
                nr_xcede_records);

        payload = &xcede_latency_parameter.payload;

        /*
         * The CEDE idle state maps to CEDE(0). While the hypervisor
         * does not advertise CEDE(0) exit latency values, it does
         * advertise the latency values of the extended CEDE states.
         * We use the lowest advertised exit latency value as a proxy
         * for the exit latency of CEDE(0).
         */
        for (i = 0; i < nr_xcede_records; i++) {
                struct xcede_latency_record *record = &payload->records[i];
                u8 hint = record->hint;
                u64 latency_tb = be64_to_cpu(record->latency_ticks);
                u64 latency_us = DIV_ROUND_UP_ULL(tb_to_ns(latency_tb), NSEC_PER_USEC);

                /*
                 * We expect the exit latency of an extended CEDE
                 * state to be non-zero, it to since it takes at least
                 * a few nanoseconds to wakeup the idle CPU and
                 * dispatch the virtual processor into the Linux
                 * Guest.
                 *
                 * So we consider only non-zero value for performing
                 * the fixup of CEDE(0) latency.
                 */
                if (latency_us == 0) {
                        pr_warn("cpuidle: Skipping xcede record %d [hint=%d]. Exit latency = 0us\n",
                                i, hint);
                        continue;
                }

                if (latency_us < min_xcede_latency_us)
                        min_xcede_latency_us = latency_us;
        }

        if (min_xcede_latency_us != UINT_MAX) {
                dedicated_states[1].exit_latency = min_xcede_latency_us;
                dedicated_states[1].target_residency = 10 * (min_xcede_latency_us);
                pr_info("cpuidle: Fixed up CEDE exit latency to %llu us\n",
                        min_xcede_latency_us);
        }

}

/*
 * pseries_idle_probe()
 * Choose state table for shared versus dedicated partition
 */
static int __init pseries_idle_probe(void)
{

        if (cpuidle_disable != IDLE_NO_OVERRIDE)
                return -ENODEV;

        if (firmware_has_feature(FW_FEATURE_SPLPAR)) {
                /*
                 * Use local_paca instead of get_lppaca() since
                 * preemption is not disabled, and it is not required in
                 * fact, since lppaca_ptr does not need to be the value
                 * associated to the current CPU, it can be from any CPU.
                 */
                if (lppaca_shared_proc(local_paca->lppaca_ptr)) {
                        cpuidle_state_table = shared_states;
                        max_idle_state = ARRAY_SIZE(shared_states);
                } else {
                        /*
                         * Use firmware provided latency values
                         * starting with POWER10 platforms. In the
                         * case that we are running on a POWER10
                         * platform but in an earlier compat mode, we
                         * can still use the firmware provided values.
                         *
                         * However, on platforms prior to POWER10, we
                         * cannot rely on the accuracy of the firmware
                         * provided latency values. On such platforms,
                         * go with the conservative default estimate
                         * of 10us.
                         */
                        if (cpu_has_feature(CPU_FTR_ARCH_31) || pvr_version_is(PVR_POWER10))
                                fixup_cede0_latency();
                        cpuidle_state_table = dedicated_states;
                        max_idle_state = NR_DEDICATED_STATES;
                }
        } else
                return -ENODEV;

        if (max_idle_state > 1) {
                snooze_timeout_en = true;
                snooze_timeout = cpuidle_state_table[1].target_residency *
                                 tb_ticks_per_usec;
        }
        return 0;
}

static int __init pseries_processor_idle_init(void)
{
        int retval;

        retval = pseries_idle_probe();
        if (retval)
                return retval;

        pseries_cpuidle_driver_init();
        retval = cpuidle_register(&pseries_idle_driver, NULL);
        if (retval) {
                printk(KERN_DEBUG "Registration of pseries driver failed.\n");
                return retval;
        }

        retval = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
                                           "cpuidle/pseries:online",
                                           pseries_cpuidle_cpu_online, NULL);
        WARN_ON(retval < 0);
        retval = cpuhp_setup_state_nocalls(CPUHP_CPUIDLE_DEAD,
                                           "cpuidle/pseries:DEAD", NULL,
                                           pseries_cpuidle_cpu_dead);
        WARN_ON(retval < 0);
        printk(KERN_DEBUG "pseries_idle_driver registered\n");
        return 0;
}

device_initcall(pseries_processor_idle_init);