Merge tag 'for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mst/vhost

[cris-mirror.git] / drivers / acpi / cppc_acpi.c

/*
 * CPPC (Collaborative Processor Performance Control) methods used by CPUfreq drivers.
 *
 * (C) Copyright 2014, 2015 Linaro Ltd.
 * Author: Ashwin Chaugule <ashwin.chaugule@linaro.org>
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; version 2
 * of the License.
 *
 * CPPC describes a few methods for controlling CPU performance using
 * information from a per CPU table called CPC. This table is described in
 * the ACPI v5.0+ specification. The table consists of a list of
 * registers which may be memory mapped or hardware registers and also may
 * include some static integer values.
 *
 * CPU performance is on an abstract continuous scale as against a discretized
 * P-state scale which is tied to CPU frequency only. In brief, the basic
 * operation involves:
 *
 * - OS makes a CPU performance request. (Can provide min and max bounds)
 *
 * - Platform (such as BMC) is free to optimize request within requested bounds
 *   depending on power/thermal budgets etc.
 *
 * - Platform conveys its decision back to OS
 *
 * The communication between OS and platform occurs through another medium
 * called (PCC) Platform Communication Channel. This is a generic mailbox like
 * mechanism which includes doorbell semantics to indicate register updates.
 * See drivers/mailbox/pcc.c for details on PCC.
 *
 * Finer details about the PCC and CPPC spec are available in the ACPI v5.1 and
 * above specifications.
 */

#define pr_fmt(fmt)     "ACPI CPPC: " fmt

#include <linux/cpufreq.h>
#include <linux/delay.h>
#include <linux/ktime.h>
#include <linux/rwsem.h>
#include <linux/wait.h>

#include <acpi/cppc_acpi.h>

struct cppc_pcc_data {
        struct mbox_chan *pcc_channel;
        void __iomem *pcc_comm_addr;
        bool pcc_channel_acquired;
        ktime_t deadline;
        unsigned int pcc_mpar, pcc_mrtt, pcc_nominal;

        bool pending_pcc_write_cmd;     /* Any pending/batched PCC write cmds? */
        bool platform_owns_pcc;         /* Ownership of PCC subspace */
        unsigned int pcc_write_cnt;     /* Running count of PCC write commands */

        /*
         * Lock to provide controlled access to the PCC channel.
         *
         * For performance critical usecases(currently cppc_set_perf)
         *      We need to take read_lock and check if channel belongs to OSPM
         * before reading or writing to PCC subspace
         *      We need to take write_lock before transferring the channel
         * ownership to the platform via a Doorbell
         *      This allows us to batch a number of CPPC requests if they happen
         * to originate in about the same time
         *
         * For non-performance critical usecases(init)
         *      Take write_lock for all purposes which gives exclusive access
         */
        struct rw_semaphore pcc_lock;

        /* Wait queue for CPUs whose requests were batched */
        wait_queue_head_t pcc_write_wait_q;
        ktime_t last_cmd_cmpl_time;
        ktime_t last_mpar_reset;
        int mpar_count;
        int refcount;
};

/* Array  to represent the PCC channel per subspace id */
static struct cppc_pcc_data *pcc_data[MAX_PCC_SUBSPACES];
/* The cpu_pcc_subspace_idx containsper CPU subspace id */
static DEFINE_PER_CPU(int, cpu_pcc_subspace_idx);

/*
 * The cpc_desc structure contains the ACPI register details
 * as described in the per CPU _CPC tables. The details
 * include the type of register (e.g. PCC, System IO, FFH etc.)
 * and destination addresses which lets us READ/WRITE CPU performance
 * information using the appropriate I/O methods.
 */
static DEFINE_PER_CPU(struct cpc_desc *, cpc_desc_ptr);

/* pcc mapped address + header size + offset within PCC subspace */
#define GET_PCC_VADDR(offs, pcc_ss_id) (pcc_data[pcc_ss_id]->pcc_comm_addr + \
                                                0x8 + (offs))

/* Check if a CPC register is in PCC */
#define CPC_IN_PCC(cpc) ((cpc)->type == ACPI_TYPE_BUFFER &&             \
                                (cpc)->cpc_entry.reg.space_id ==        \
                                ACPI_ADR_SPACE_PLATFORM_COMM)

/* Evalutes to True if reg is a NULL register descriptor */
#define IS_NULL_REG(reg) ((reg)->space_id ==  ACPI_ADR_SPACE_SYSTEM_MEMORY && \
                                (reg)->address == 0 &&                  \
                                (reg)->bit_width == 0 &&                \
                                (reg)->bit_offset == 0 &&               \
                                (reg)->access_width == 0)

/* Evalutes to True if an optional cpc field is supported */
#define CPC_SUPPORTED(cpc) ((cpc)->type == ACPI_TYPE_INTEGER ?          \
                                !!(cpc)->cpc_entry.int_value :          \
                                !IS_NULL_REG(&(cpc)->cpc_entry.reg))
/*
 * Arbitrary Retries in case the remote processor is slow to respond
 * to PCC commands. Keeping it high enough to cover emulators where
 * the processors run painfully slow.
 */
#define NUM_RETRIES 500ULL

struct cppc_attr {
        struct attribute attr;
        ssize_t (*show)(struct kobject *kobj,
                        struct attribute *attr, char *buf);
        ssize_t (*store)(struct kobject *kobj,
                        struct attribute *attr, const char *c, ssize_t count);
};

#define define_one_cppc_ro(_name)               \
static struct cppc_attr _name =                 \
__ATTR(_name, 0444, show_##_name, NULL)

#define to_cpc_desc(a) container_of(a, struct cpc_desc, kobj)

#define show_cppc_data(access_fn, struct_name, member_name)             \
        static ssize_t show_##member_name(struct kobject *kobj,         \
                                        struct attribute *attr, char *buf) \
        {                                                               \
                struct cpc_desc *cpc_ptr = to_cpc_desc(kobj);           \
                struct struct_name st_name = {0};                       \
                int ret;                                                \
                                                                        \
                ret = access_fn(cpc_ptr->cpu_id, &st_name);             \
                if (ret)                                                \
                        return ret;                                     \
                                                                        \
                return scnprintf(buf, PAGE_SIZE, "%llu\n",              \
                                (u64)st_name.member_name);              \
        }                                                               \
        define_one_cppc_ro(member_name)

show_cppc_data(cppc_get_perf_caps, cppc_perf_caps, highest_perf);
show_cppc_data(cppc_get_perf_caps, cppc_perf_caps, lowest_perf);
show_cppc_data(cppc_get_perf_caps, cppc_perf_caps, nominal_perf);
show_cppc_data(cppc_get_perf_caps, cppc_perf_caps, lowest_nonlinear_perf);
show_cppc_data(cppc_get_perf_ctrs, cppc_perf_fb_ctrs, reference_perf);
show_cppc_data(cppc_get_perf_ctrs, cppc_perf_fb_ctrs, wraparound_time);

static ssize_t show_feedback_ctrs(struct kobject *kobj,
                struct attribute *attr, char *buf)
{
        struct cpc_desc *cpc_ptr = to_cpc_desc(kobj);
        struct cppc_perf_fb_ctrs fb_ctrs = {0};
        int ret;

        ret = cppc_get_perf_ctrs(cpc_ptr->cpu_id, &fb_ctrs);
        if (ret)
                return ret;

        return scnprintf(buf, PAGE_SIZE, "ref:%llu del:%llu\n",
                        fb_ctrs.reference, fb_ctrs.delivered);
}
define_one_cppc_ro(feedback_ctrs);

static struct attribute *cppc_attrs[] = {
        &feedback_ctrs.attr,
        &reference_perf.attr,
        &wraparound_time.attr,
        &highest_perf.attr,
        &lowest_perf.attr,
        &lowest_nonlinear_perf.attr,
        &nominal_perf.attr,
        NULL
};

static struct kobj_type cppc_ktype = {
        .sysfs_ops = &kobj_sysfs_ops,
        .default_attrs = cppc_attrs,
};

static int check_pcc_chan(int pcc_ss_id, bool chk_err_bit)
{
        int ret = -EIO, status = 0;
        struct cppc_pcc_data *pcc_ss_data = pcc_data[pcc_ss_id];
        struct acpi_pcct_shared_memory __iomem *generic_comm_base =
                pcc_ss_data->pcc_comm_addr;
        ktime_t next_deadline = ktime_add(ktime_get(),
                                          pcc_ss_data->deadline);

        if (!pcc_ss_data->platform_owns_pcc)
                return 0;

        /* Retry in case the remote processor was too slow to catch up. */
        while (!ktime_after(ktime_get(), next_deadline)) {
                /*
                 * Per spec, prior to boot the PCC space wil be initialized by
                 * platform and should have set the command completion bit when
                 * PCC can be used by OSPM
                 */
                status = readw_relaxed(&generic_comm_base->status);
                if (status & PCC_CMD_COMPLETE_MASK) {
                        ret = 0;
                        if (chk_err_bit && (status & PCC_ERROR_MASK))
                                ret = -EIO;
                        break;
                }
                /*
                 * Reducing the bus traffic in case this loop takes longer than
                 * a few retries.
                 */
                udelay(3);
        }

        if (likely(!ret))
                pcc_ss_data->platform_owns_pcc = false;
        else
                pr_err("PCC check channel failed. Status=%x\n", status);

        return ret;
}

/*
 * This function transfers the ownership of the PCC to the platform
 * So it must be called while holding write_lock(pcc_lock)
 */
static int send_pcc_cmd(int pcc_ss_id, u16 cmd)
{
        int ret = -EIO, i;
        struct cppc_pcc_data *pcc_ss_data = pcc_data[pcc_ss_id];
        struct acpi_pcct_shared_memory *generic_comm_base =
                (struct acpi_pcct_shared_memory *)pcc_ss_data->pcc_comm_addr;
        unsigned int time_delta;

        /*
         * For CMD_WRITE we know for a fact the caller should have checked
         * the channel before writing to PCC space
         */
        if (cmd == CMD_READ) {
                /*
                 * If there are pending cpc_writes, then we stole the channel
                 * before write completion, so first send a WRITE command to
                 * platform
                 */
                if (pcc_ss_data->pending_pcc_write_cmd)
                        send_pcc_cmd(pcc_ss_id, CMD_WRITE);

                ret = check_pcc_chan(pcc_ss_id, false);
                if (ret)
                        goto end;
        } else /* CMD_WRITE */
                pcc_ss_data->pending_pcc_write_cmd = FALSE;

        /*
         * Handle the Minimum Request Turnaround Time(MRTT)
         * "The minimum amount of time that OSPM must wait after the completion
         * of a command before issuing the next command, in microseconds"
         */
        if (pcc_ss_data->pcc_mrtt) {
                time_delta = ktime_us_delta(ktime_get(),
                                            pcc_ss_data->last_cmd_cmpl_time);
                if (pcc_ss_data->pcc_mrtt > time_delta)
                        udelay(pcc_ss_data->pcc_mrtt - time_delta);
        }

        /*
         * Handle the non-zero Maximum Periodic Access Rate(MPAR)
         * "The maximum number of periodic requests that the subspace channel can
         * support, reported in commands per minute. 0 indicates no limitation."
         *
         * This parameter should be ideally zero or large enough so that it can
         * handle maximum number of requests that all the cores in the system can
         * collectively generate. If it is not, we will follow the spec and just
         * not send the request to the platform after hitting the MPAR limit in
         * any 60s window
         */
        if (pcc_ss_data->pcc_mpar) {
                if (pcc_ss_data->mpar_count == 0) {
                        time_delta = ktime_ms_delta(ktime_get(),
                                                    pcc_ss_data->last_mpar_reset);
                        if ((time_delta < 60 * MSEC_PER_SEC) && pcc_ss_data->last_mpar_reset) {
                                pr_debug("PCC cmd not sent due to MPAR limit");
                                ret = -EIO;
                                goto end;
                        }
                        pcc_ss_data->last_mpar_reset = ktime_get();
                        pcc_ss_data->mpar_count = pcc_ss_data->pcc_mpar;
                }
                pcc_ss_data->mpar_count--;
        }

        /* Write to the shared comm region. */
        writew_relaxed(cmd, &generic_comm_base->command);

        /* Flip CMD COMPLETE bit */
        writew_relaxed(0, &generic_comm_base->status);

        pcc_ss_data->platform_owns_pcc = true;

        /* Ring doorbell */
        ret = mbox_send_message(pcc_ss_data->pcc_channel, &cmd);
        if (ret < 0) {
                pr_err("Err sending PCC mbox message. cmd:%d, ret:%d\n",
                                cmd, ret);
                goto end;
        }

        /* wait for completion and check for PCC errro bit */
        ret = check_pcc_chan(pcc_ss_id, true);

        if (pcc_ss_data->pcc_mrtt)
                pcc_ss_data->last_cmd_cmpl_time = ktime_get();

        if (pcc_ss_data->pcc_channel->mbox->txdone_irq)
                mbox_chan_txdone(pcc_ss_data->pcc_channel, ret);
        else
                mbox_client_txdone(pcc_ss_data->pcc_channel, ret);

end:
        if (cmd == CMD_WRITE) {
                if (unlikely(ret)) {
                        for_each_possible_cpu(i) {
                                struct cpc_desc *desc = per_cpu(cpc_desc_ptr, i);
                                if (!desc)
                                        continue;

                                if (desc->write_cmd_id == pcc_ss_data->pcc_write_cnt)
                                        desc->write_cmd_status = ret;
                        }
                }
                pcc_ss_data->pcc_write_cnt++;
                wake_up_all(&pcc_ss_data->pcc_write_wait_q);
        }

        return ret;
}

static void cppc_chan_tx_done(struct mbox_client *cl, void *msg, int ret)
{
        if (ret < 0)
                pr_debug("TX did not complete: CMD sent:%x, ret:%d\n",
                                *(u16 *)msg, ret);
        else
                pr_debug("TX completed. CMD sent:%x, ret:%d\n",
                                *(u16 *)msg, ret);
}

struct mbox_client cppc_mbox_cl = {
        .tx_done = cppc_chan_tx_done,
        .knows_txdone = true,
};

static int acpi_get_psd(struct cpc_desc *cpc_ptr, acpi_handle handle)
{
        int result = -EFAULT;
        acpi_status status = AE_OK;
        struct acpi_buffer buffer = {ACPI_ALLOCATE_BUFFER, NULL};
        struct acpi_buffer format = {sizeof("NNNNN"), "NNNNN"};
        struct acpi_buffer state = {0, NULL};
        union acpi_object  *psd = NULL;
        struct acpi_psd_package *pdomain;

        status = acpi_evaluate_object_typed(handle, "_PSD", NULL, &buffer,
                        ACPI_TYPE_PACKAGE);
        if (ACPI_FAILURE(status))
                return -ENODEV;

        psd = buffer.pointer;
        if (!psd || psd->package.count != 1) {
                pr_debug("Invalid _PSD data\n");
                goto end;
        }

        pdomain = &(cpc_ptr->domain_info);

        state.length = sizeof(struct acpi_psd_package);
        state.pointer = pdomain;

        status = acpi_extract_package(&(psd->package.elements[0]),
                &format, &state);
        if (ACPI_FAILURE(status)) {
                pr_debug("Invalid _PSD data for CPU:%d\n", cpc_ptr->cpu_id);
                goto end;
        }

        if (pdomain->num_entries != ACPI_PSD_REV0_ENTRIES) {
                pr_debug("Unknown _PSD:num_entries for CPU:%d\n", cpc_ptr->cpu_id);
                goto end;
        }

        if (pdomain->revision != ACPI_PSD_REV0_REVISION) {
                pr_debug("Unknown _PSD:revision for CPU: %d\n", cpc_ptr->cpu_id);
                goto end;
        }

        if (pdomain->coord_type != DOMAIN_COORD_TYPE_SW_ALL &&
            pdomain->coord_type != DOMAIN_COORD_TYPE_SW_ANY &&
            pdomain->coord_type != DOMAIN_COORD_TYPE_HW_ALL) {
                pr_debug("Invalid _PSD:coord_type for CPU:%d\n", cpc_ptr->cpu_id);
                goto end;
        }

        result = 0;
end:
        kfree(buffer.pointer);
        return result;
}

/**
 * acpi_get_psd_map - Map the CPUs in a common freq domain.
 * @all_cpu_data: Ptrs to CPU specific CPPC data including PSD info.
 *
 *      Return: 0 for success or negative value for err.
 */
int acpi_get_psd_map(struct cppc_cpudata **all_cpu_data)
{
        int count_target;
        int retval = 0;
        unsigned int i, j;
        cpumask_var_t covered_cpus;
        struct cppc_cpudata *pr, *match_pr;
        struct acpi_psd_package *pdomain;
        struct acpi_psd_package *match_pdomain;
        struct cpc_desc *cpc_ptr, *match_cpc_ptr;

        if (!zalloc_cpumask_var(&covered_cpus, GFP_KERNEL))
                return -ENOMEM;

        /*
         * Now that we have _PSD data from all CPUs, lets setup P-state
         * domain info.
         */
        for_each_possible_cpu(i) {
                pr = all_cpu_data[i];
                if (!pr)
                        continue;

                if (cpumask_test_cpu(i, covered_cpus))
                        continue;

                cpc_ptr = per_cpu(cpc_desc_ptr, i);
                if (!cpc_ptr) {
                        retval = -EFAULT;
                        goto err_ret;
                }

                pdomain = &(cpc_ptr->domain_info);
                cpumask_set_cpu(i, pr->shared_cpu_map);
                cpumask_set_cpu(i, covered_cpus);
                if (pdomain->num_processors <= 1)
                        continue;

                /* Validate the Domain info */
                count_target = pdomain->num_processors;
                if (pdomain->coord_type == DOMAIN_COORD_TYPE_SW_ALL)
                        pr->shared_type = CPUFREQ_SHARED_TYPE_ALL;
                else if (pdomain->coord_type == DOMAIN_COORD_TYPE_HW_ALL)
                        pr->shared_type = CPUFREQ_SHARED_TYPE_HW;
                else if (pdomain->coord_type == DOMAIN_COORD_TYPE_SW_ANY)
                        pr->shared_type = CPUFREQ_SHARED_TYPE_ANY;

                for_each_possible_cpu(j) {
                        if (i == j)
                                continue;

                        match_cpc_ptr = per_cpu(cpc_desc_ptr, j);
                        if (!match_cpc_ptr) {
                                retval = -EFAULT;
                                goto err_ret;
                        }

                        match_pdomain = &(match_cpc_ptr->domain_info);
                        if (match_pdomain->domain != pdomain->domain)
                                continue;

                        /* Here i and j are in the same domain */
                        if (match_pdomain->num_processors != count_target) {
                                retval = -EFAULT;
                                goto err_ret;
                        }

                        if (pdomain->coord_type != match_pdomain->coord_type) {
                                retval = -EFAULT;
                                goto err_ret;
                        }

                        cpumask_set_cpu(j, covered_cpus);
                        cpumask_set_cpu(j, pr->shared_cpu_map);
                }

                for_each_possible_cpu(j) {
                        if (i == j)
                                continue;

                        match_pr = all_cpu_data[j];
                        if (!match_pr)
                                continue;

                        match_cpc_ptr = per_cpu(cpc_desc_ptr, j);
                        if (!match_cpc_ptr) {
                                retval = -EFAULT;
                                goto err_ret;
                        }

                        match_pdomain = &(match_cpc_ptr->domain_info);
                        if (match_pdomain->domain != pdomain->domain)
                                continue;

                        match_pr->shared_type = pr->shared_type;
                        cpumask_copy(match_pr->shared_cpu_map,
                                     pr->shared_cpu_map);
                }
        }

err_ret:
        for_each_possible_cpu(i) {
                pr = all_cpu_data[i];
                if (!pr)
                        continue;

                /* Assume no coordination on any error parsing domain info */
                if (retval) {
                        cpumask_clear(pr->shared_cpu_map);
                        cpumask_set_cpu(i, pr->shared_cpu_map);
                        pr->shared_type = CPUFREQ_SHARED_TYPE_ALL;
                }
        }

        free_cpumask_var(covered_cpus);
        return retval;
}
EXPORT_SYMBOL_GPL(acpi_get_psd_map);

static int register_pcc_channel(int pcc_ss_idx)
{
        struct acpi_pcct_hw_reduced *cppc_ss;
        u64 usecs_lat;

        if (pcc_ss_idx >= 0) {
                pcc_data[pcc_ss_idx]->pcc_channel =
                        pcc_mbox_request_channel(&cppc_mbox_cl, pcc_ss_idx);

                if (IS_ERR(pcc_data[pcc_ss_idx]->pcc_channel)) {
                        pr_err("Failed to find PCC communication channel\n");
                        return -ENODEV;
                }

                /*
                 * The PCC mailbox controller driver should
                 * have parsed the PCCT (global table of all
                 * PCC channels) and stored pointers to the
                 * subspace communication region in con_priv.
                 */
                cppc_ss = (pcc_data[pcc_ss_idx]->pcc_channel)->con_priv;

                if (!cppc_ss) {
                        pr_err("No PCC subspace found for CPPC\n");
                        return -ENODEV;
                }

                /*
                 * cppc_ss->latency is just a Nominal value. In reality
                 * the remote processor could be much slower to reply.
                 * So add an arbitrary amount of wait on top of Nominal.
                 */
                usecs_lat = NUM_RETRIES * cppc_ss->latency;
                pcc_data[pcc_ss_idx]->deadline = ns_to_ktime(usecs_lat * NSEC_PER_USEC);
                pcc_data[pcc_ss_idx]->pcc_mrtt = cppc_ss->min_turnaround_time;
                pcc_data[pcc_ss_idx]->pcc_mpar = cppc_ss->max_access_rate;
                pcc_data[pcc_ss_idx]->pcc_nominal = cppc_ss->latency;

                pcc_data[pcc_ss_idx]->pcc_comm_addr =
                        acpi_os_ioremap(cppc_ss->base_address, cppc_ss->length);
                if (!pcc_data[pcc_ss_idx]->pcc_comm_addr) {
                        pr_err("Failed to ioremap PCC comm region mem\n");
                        return -ENOMEM;
                }

                /* Set flag so that we dont come here for each CPU. */
                pcc_data[pcc_ss_idx]->pcc_channel_acquired = true;
        }

        return 0;
}

/**
 * cpc_ffh_supported() - check if FFH reading supported
 *
 * Check if the architecture has support for functional fixed hardware
 * read/write capability.
 *
 * Return: true for supported, false for not supported
 */
bool __weak cpc_ffh_supported(void)
{
        return false;
}


/**
 * pcc_data_alloc() - Allocate the pcc_data memory for pcc subspace
 *
 * Check and allocate the cppc_pcc_data memory.
 * In some processor configurations it is possible that same subspace
 * is shared between multiple CPU's. This is seen especially in CPU's
 * with hardware multi-threading support.
 *
 * Return: 0 for success, errno for failure
 */
int pcc_data_alloc(int pcc_ss_id)
{
        if (pcc_ss_id < 0 || pcc_ss_id >= MAX_PCC_SUBSPACES)
                return -EINVAL;

        if (pcc_data[pcc_ss_id]) {
                pcc_data[pcc_ss_id]->refcount++;
        } else {
                pcc_data[pcc_ss_id] = kzalloc(sizeof(struct cppc_pcc_data),
                                              GFP_KERNEL);
                if (!pcc_data[pcc_ss_id])
                        return -ENOMEM;
                pcc_data[pcc_ss_id]->refcount++;
        }

        return 0;
}
/*
 * An example CPC table looks like the following.
 *
 *      Name(_CPC, Package()
 *                      {
 *                      17,
 *                      NumEntries
 *                      1,
 *                      // Revision
 *                      ResourceTemplate(){Register(PCC, 32, 0, 0x120, 2)},
 *                      // Highest Performance
 *                      ResourceTemplate(){Register(PCC, 32, 0, 0x124, 2)},
 *                      // Nominal Performance
 *                      ResourceTemplate(){Register(PCC, 32, 0, 0x128, 2)},
 *                      // Lowest Nonlinear Performance
 *                      ResourceTemplate(){Register(PCC, 32, 0, 0x12C, 2)},
 *                      // Lowest Performance
 *                      ResourceTemplate(){Register(PCC, 32, 0, 0x130, 2)},
 *                      // Guaranteed Performance Register
 *                      ResourceTemplate(){Register(PCC, 32, 0, 0x110, 2)},
 *                      // Desired Performance Register
 *                      ResourceTemplate(){Register(SystemMemory, 0, 0, 0, 0)},
 *                      ..
 *                      ..
 *                      ..
 *
 *              }
 * Each Register() encodes how to access that specific register.
 * e.g. a sample PCC entry has the following encoding:
 *
 *      Register (
 *              PCC,
 *              AddressSpaceKeyword
 *              8,
 *              //RegisterBitWidth
 *              8,
 *              //RegisterBitOffset
 *              0x30,
 *              //RegisterAddress
 *              9
 *              //AccessSize (subspace ID)
 *              0
 *              )
 *      }
 */

/**
 * acpi_cppc_processor_probe - Search for per CPU _CPC objects.
 * @pr: Ptr to acpi_processor containing this CPUs logical Id.
 *
 *      Return: 0 for success or negative value for err.
 */
int acpi_cppc_processor_probe(struct acpi_processor *pr)
{
        struct acpi_buffer output = {ACPI_ALLOCATE_BUFFER, NULL};
        union acpi_object *out_obj, *cpc_obj;
        struct cpc_desc *cpc_ptr;
        struct cpc_reg *gas_t;
        struct device *cpu_dev;
        acpi_handle handle = pr->handle;
        unsigned int num_ent, i, cpc_rev;
        int pcc_subspace_id = -1;
        acpi_status status;
        int ret = -EFAULT;

        /* Parse the ACPI _CPC table for this cpu. */
        status = acpi_evaluate_object_typed(handle, "_CPC", NULL, &output,
                        ACPI_TYPE_PACKAGE);
        if (ACPI_FAILURE(status)) {
                ret = -ENODEV;
                goto out_buf_free;
        }

        out_obj = (union acpi_object *) output.pointer;

        cpc_ptr = kzalloc(sizeof(struct cpc_desc), GFP_KERNEL);
        if (!cpc_ptr) {
                ret = -ENOMEM;
                goto out_buf_free;
        }

        /* First entry is NumEntries. */
        cpc_obj = &out_obj->package.elements[0];
        if (cpc_obj->type == ACPI_TYPE_INTEGER) {
                num_ent = cpc_obj->integer.value;
        } else {
                pr_debug("Unexpected entry type(%d) for NumEntries\n",
                                cpc_obj->type);
                goto out_free;
        }

        /* Only support CPPCv2. Bail otherwise. */
        if (num_ent != CPPC_NUM_ENT) {
                pr_debug("Firmware exports %d entries. Expected: %d\n",
                                num_ent, CPPC_NUM_ENT);
                goto out_free;
        }

        cpc_ptr->num_entries = num_ent;

        /* Second entry should be revision. */
        cpc_obj = &out_obj->package.elements[1];
        if (cpc_obj->type == ACPI_TYPE_INTEGER) {
                cpc_rev = cpc_obj->integer.value;
        } else {
                pr_debug("Unexpected entry type(%d) for Revision\n",
                                cpc_obj->type);
                goto out_free;
        }

        if (cpc_rev != CPPC_REV) {
                pr_debug("Firmware exports revision:%d. Expected:%d\n",
                                cpc_rev, CPPC_REV);
                goto out_free;
        }

        /* Iterate through remaining entries in _CPC */
        for (i = 2; i < num_ent; i++) {
                cpc_obj = &out_obj->package.elements[i];

                if (cpc_obj->type == ACPI_TYPE_INTEGER) {
                        cpc_ptr->cpc_regs[i-2].type = ACPI_TYPE_INTEGER;
                        cpc_ptr->cpc_regs[i-2].cpc_entry.int_value = cpc_obj->integer.value;
                } else if (cpc_obj->type == ACPI_TYPE_BUFFER) {
                        gas_t = (struct cpc_reg *)
                                cpc_obj->buffer.pointer;

                        /*
                         * The PCC Subspace index is encoded inside
                         * the CPC table entries. The same PCC index
                         * will be used for all the PCC entries,
                         * so extract it only once.
                         */
                        if (gas_t->space_id == ACPI_ADR_SPACE_PLATFORM_COMM) {
                                if (pcc_subspace_id < 0) {
                                        pcc_subspace_id = gas_t->access_width;
                                        if (pcc_data_alloc(pcc_subspace_id))
                                                goto out_free;
                                } else if (pcc_subspace_id != gas_t->access_width) {
                                        pr_debug("Mismatched PCC ids.\n");
                                        goto out_free;
                                }
                        } else if (gas_t->space_id == ACPI_ADR_SPACE_SYSTEM_MEMORY) {
                                if (gas_t->address) {
                                        void __iomem *addr;

                                        addr = ioremap(gas_t->address, gas_t->bit_width/8);
                                        if (!addr)
                                                goto out_free;
                                        cpc_ptr->cpc_regs[i-2].sys_mem_vaddr = addr;
                                }
                        } else {
                                if (gas_t->space_id != ACPI_ADR_SPACE_FIXED_HARDWARE || !cpc_ffh_supported()) {
                                        /* Support only PCC ,SYS MEM and FFH type regs */
                                        pr_debug("Unsupported register type: %d\n", gas_t->space_id);
                                        goto out_free;
                                }
                        }

                        cpc_ptr->cpc_regs[i-2].type = ACPI_TYPE_BUFFER;
                        memcpy(&cpc_ptr->cpc_regs[i-2].cpc_entry.reg, gas_t, sizeof(*gas_t));
                } else {
                        pr_debug("Err in entry:%d in CPC table of CPU:%d \n", i, pr->id);
                        goto out_free;
                }
        }
        per_cpu(cpu_pcc_subspace_idx, pr->id) = pcc_subspace_id;
        /* Store CPU Logical ID */
        cpc_ptr->cpu_id = pr->id;

        /* Parse PSD data for this CPU */
        ret = acpi_get_psd(cpc_ptr, handle);
        if (ret)
                goto out_free;

        /* Register PCC channel once for all PCC subspace id. */
        if (pcc_subspace_id >= 0 && !pcc_data[pcc_subspace_id]->pcc_channel_acquired) {
                ret = register_pcc_channel(pcc_subspace_id);
                if (ret)
                        goto out_free;

                init_rwsem(&pcc_data[pcc_subspace_id]->pcc_lock);
                init_waitqueue_head(&pcc_data[pcc_subspace_id]->pcc_write_wait_q);
        }

        /* Everything looks okay */
        pr_debug("Parsed CPC struct for CPU: %d\n", pr->id);

        /* Add per logical CPU nodes for reading its feedback counters. */
        cpu_dev = get_cpu_device(pr->id);
        if (!cpu_dev) {
                ret = -EINVAL;
                goto out_free;
        }

        /* Plug PSD data into this CPUs CPC descriptor. */
        per_cpu(cpc_desc_ptr, pr->id) = cpc_ptr;

        ret = kobject_init_and_add(&cpc_ptr->kobj, &cppc_ktype, &cpu_dev->kobj,
                        "acpi_cppc");
        if (ret) {
                per_cpu(cpc_desc_ptr, pr->id) = NULL;
                goto out_free;
        }

        kfree(output.pointer);
        return 0;

out_free:
        /* Free all the mapped sys mem areas for this CPU */
        for (i = 2; i < cpc_ptr->num_entries; i++) {
                void __iomem *addr = cpc_ptr->cpc_regs[i-2].sys_mem_vaddr;

                if (addr)
                        iounmap(addr);
        }
        kfree(cpc_ptr);

out_buf_free:
        kfree(output.pointer);
        return ret;
}
EXPORT_SYMBOL_GPL(acpi_cppc_processor_probe);

/**
 * acpi_cppc_processor_exit - Cleanup CPC structs.
 * @pr: Ptr to acpi_processor containing this CPUs logical Id.
 *
 * Return: Void
 */
void acpi_cppc_processor_exit(struct acpi_processor *pr)
{
        struct cpc_desc *cpc_ptr;
        unsigned int i;
        void __iomem *addr;
        int pcc_ss_id = per_cpu(cpu_pcc_subspace_idx, pr->id);

        if (pcc_ss_id >=0 && pcc_data[pcc_ss_id]) {
                if (pcc_data[pcc_ss_id]->pcc_channel_acquired) {
                        pcc_data[pcc_ss_id]->refcount--;
                        if (!pcc_data[pcc_ss_id]->refcount) {
                                pcc_mbox_free_channel(pcc_data[pcc_ss_id]->pcc_channel);
                                pcc_data[pcc_ss_id]->pcc_channel_acquired = 0;
                                kfree(pcc_data[pcc_ss_id]);
                        }
                }
        }

        cpc_ptr = per_cpu(cpc_desc_ptr, pr->id);
        if (!cpc_ptr)
                return;

        /* Free all the mapped sys mem areas for this CPU */
        for (i = 2; i < cpc_ptr->num_entries; i++) {
                addr = cpc_ptr->cpc_regs[i-2].sys_mem_vaddr;
                if (addr)
                        iounmap(addr);
        }

        kobject_put(&cpc_ptr->kobj);
        kfree(cpc_ptr);
}
EXPORT_SYMBOL_GPL(acpi_cppc_processor_exit);

/**
 * cpc_read_ffh() - Read FFH register
 * @cpunum:     cpu number to read
 * @reg:        cppc register information
 * @val:        place holder for return value
 *
 * Read bit_width bits from a specified address and bit_offset
 *
 * Return: 0 for success and error code
 */
int __weak cpc_read_ffh(int cpunum, struct cpc_reg *reg, u64 *val)
{
        return -ENOTSUPP;
}

/**
 * cpc_write_ffh() - Write FFH register
 * @cpunum:     cpu number to write
 * @reg:        cppc register information
 * @val:        value to write
 *
 * Write value of bit_width bits to a specified address and bit_offset
 *
 * Return: 0 for success and error code
 */
int __weak cpc_write_ffh(int cpunum, struct cpc_reg *reg, u64 val)
{
        return -ENOTSUPP;
}

/*
 * Since cpc_read and cpc_write are called while holding pcc_lock, it should be
 * as fast as possible. We have already mapped the PCC subspace during init, so
 * we can directly write to it.
 */

static int cpc_read(int cpu, struct cpc_register_resource *reg_res, u64 *val)
{
        int ret_val = 0;
        void __iomem *vaddr = 0;
        int pcc_ss_id = per_cpu(cpu_pcc_subspace_idx, cpu);
        struct cpc_reg *reg = &reg_res->cpc_entry.reg;

        if (reg_res->type == ACPI_TYPE_INTEGER) {
                *val = reg_res->cpc_entry.int_value;
                return ret_val;
        }

        *val = 0;
        if (reg->space_id == ACPI_ADR_SPACE_PLATFORM_COMM && pcc_ss_id >= 0)
                vaddr = GET_PCC_VADDR(reg->address, pcc_ss_id);
        else if (reg->space_id == ACPI_ADR_SPACE_SYSTEM_MEMORY)
                vaddr = reg_res->sys_mem_vaddr;
        else if (reg->space_id == ACPI_ADR_SPACE_FIXED_HARDWARE)
                return cpc_read_ffh(cpu, reg, val);
        else
                return acpi_os_read_memory((acpi_physical_address)reg->address,
                                val, reg->bit_width);

        switch (reg->bit_width) {
                case 8:
                        *val = readb_relaxed(vaddr);
                        break;
                case 16:
                        *val = readw_relaxed(vaddr);
                        break;
                case 32:
                        *val = readl_relaxed(vaddr);
                        break;
                case 64:
                        *val = readq_relaxed(vaddr);
                        break;
                default:
                        pr_debug("Error: Cannot read %u bit width from PCC\n",
                                        reg->bit_width);
                        ret_val = -EFAULT;
        }

        return ret_val;
}

static int cpc_write(int cpu, struct cpc_register_resource *reg_res, u64 val)
{
        int ret_val = 0;
        void __iomem *vaddr = 0;
        int pcc_ss_id = per_cpu(cpu_pcc_subspace_idx, cpu);
        struct cpc_reg *reg = &reg_res->cpc_entry.reg;

        if (reg->space_id == ACPI_ADR_SPACE_PLATFORM_COMM && pcc_ss_id >= 0)
                vaddr = GET_PCC_VADDR(reg->address, pcc_ss_id);
        else if (reg->space_id == ACPI_ADR_SPACE_SYSTEM_MEMORY)
                vaddr = reg_res->sys_mem_vaddr;
        else if (reg->space_id == ACPI_ADR_SPACE_FIXED_HARDWARE)
                return cpc_write_ffh(cpu, reg, val);
        else
                return acpi_os_write_memory((acpi_physical_address)reg->address,
                                val, reg->bit_width);

        switch (reg->bit_width) {
                case 8:
                        writeb_relaxed(val, vaddr);
                        break;
                case 16:
                        writew_relaxed(val, vaddr);
                        break;
                case 32:
                        writel_relaxed(val, vaddr);
                        break;
                case 64:
                        writeq_relaxed(val, vaddr);
                        break;
                default:
                        pr_debug("Error: Cannot write %u bit width to PCC\n",
                                        reg->bit_width);
                        ret_val = -EFAULT;
                        break;
        }

        return ret_val;
}

/**
 * cppc_get_perf_caps - Get a CPUs performance capabilities.
 * @cpunum: CPU from which to get capabilities info.
 * @perf_caps: ptr to cppc_perf_caps. See cppc_acpi.h
 *
 * Return: 0 for success with perf_caps populated else -ERRNO.
 */
int cppc_get_perf_caps(int cpunum, struct cppc_perf_caps *perf_caps)
{
        struct cpc_desc *cpc_desc = per_cpu(cpc_desc_ptr, cpunum);
        struct cpc_register_resource *highest_reg, *lowest_reg,
                *lowest_non_linear_reg, *nominal_reg;
        u64 high, low, nom, min_nonlinear;
        int pcc_ss_id = per_cpu(cpu_pcc_subspace_idx, cpunum);
        struct cppc_pcc_data *pcc_ss_data;
        int ret = 0, regs_in_pcc = 0;

        if (!cpc_desc || pcc_ss_id < 0) {
                pr_debug("No CPC descriptor for CPU:%d\n", cpunum);
                return -ENODEV;
        }

        pcc_ss_data = pcc_data[pcc_ss_id];
        highest_reg = &cpc_desc->cpc_regs[HIGHEST_PERF];
        lowest_reg = &cpc_desc->cpc_regs[LOWEST_PERF];
        lowest_non_linear_reg = &cpc_desc->cpc_regs[LOW_NON_LINEAR_PERF];
        nominal_reg = &cpc_desc->cpc_regs[NOMINAL_PERF];

        /* Are any of the regs PCC ?*/
        if (CPC_IN_PCC(highest_reg) || CPC_IN_PCC(lowest_reg) ||
                CPC_IN_PCC(lowest_non_linear_reg) || CPC_IN_PCC(nominal_reg)) {
                regs_in_pcc = 1;
                down_write(&pcc_ss_data->pcc_lock);
                /* Ring doorbell once to update PCC subspace */
                if (send_pcc_cmd(pcc_ss_id, CMD_READ) < 0) {
                        ret = -EIO;
                        goto out_err;
                }
        }

        cpc_read(cpunum, highest_reg, &high);
        perf_caps->highest_perf = high;

        cpc_read(cpunum, lowest_reg, &low);
        perf_caps->lowest_perf = low;

        cpc_read(cpunum, nominal_reg, &nom);
        perf_caps->nominal_perf = nom;

        cpc_read(cpunum, lowest_non_linear_reg, &min_nonlinear);
        perf_caps->lowest_nonlinear_perf = min_nonlinear;

        if (!high || !low || !nom || !min_nonlinear)
                ret = -EFAULT;

out_err:
        if (regs_in_pcc)
                up_write(&pcc_ss_data->pcc_lock);
        return ret;
}
EXPORT_SYMBOL_GPL(cppc_get_perf_caps);

/**
 * cppc_get_perf_ctrs - Read a CPUs performance feedback counters.
 * @cpunum: CPU from which to read counters.
 * @perf_fb_ctrs: ptr to cppc_perf_fb_ctrs. See cppc_acpi.h
 *
 * Return: 0 for success with perf_fb_ctrs populated else -ERRNO.
 */
int cppc_get_perf_ctrs(int cpunum, struct cppc_perf_fb_ctrs *perf_fb_ctrs)
{
        struct cpc_desc *cpc_desc = per_cpu(cpc_desc_ptr, cpunum);
        struct cpc_register_resource *delivered_reg, *reference_reg,
                *ref_perf_reg, *ctr_wrap_reg;
        int pcc_ss_id = per_cpu(cpu_pcc_subspace_idx, cpunum);
        struct cppc_pcc_data *pcc_ss_data;
        u64 delivered, reference, ref_perf, ctr_wrap_time;
        int ret = 0, regs_in_pcc = 0;

        if (!cpc_desc || pcc_ss_id < 0) {
                pr_debug("No CPC descriptor for CPU:%d\n", cpunum);
                return -ENODEV;
        }

        pcc_ss_data = pcc_data[pcc_ss_id];
        delivered_reg = &cpc_desc->cpc_regs[DELIVERED_CTR];
        reference_reg = &cpc_desc->cpc_regs[REFERENCE_CTR];
        ref_perf_reg = &cpc_desc->cpc_regs[REFERENCE_PERF];
        ctr_wrap_reg = &cpc_desc->cpc_regs[CTR_WRAP_TIME];

        /*
         * If refernce perf register is not supported then we should
         * use the nominal perf value
         */
        if (!CPC_SUPPORTED(ref_perf_reg))
                ref_perf_reg = &cpc_desc->cpc_regs[NOMINAL_PERF];

        /* Are any of the regs PCC ?*/
        if (CPC_IN_PCC(delivered_reg) || CPC_IN_PCC(reference_reg) ||
                CPC_IN_PCC(ctr_wrap_reg) || CPC_IN_PCC(ref_perf_reg)) {
                down_write(&pcc_ss_data->pcc_lock);
                regs_in_pcc = 1;
                /* Ring doorbell once to update PCC subspace */
                if (send_pcc_cmd(pcc_ss_id, CMD_READ) < 0) {
                        ret = -EIO;
                        goto out_err;
                }
        }

        cpc_read(cpunum, delivered_reg, &delivered);
        cpc_read(cpunum, reference_reg, &reference);
        cpc_read(cpunum, ref_perf_reg, &ref_perf);

        /*
         * Per spec, if ctr_wrap_time optional register is unsupported, then the
         * performance counters are assumed to never wrap during the lifetime of
         * platform
         */
        ctr_wrap_time = (u64)(~((u64)0));
        if (CPC_SUPPORTED(ctr_wrap_reg))
                cpc_read(cpunum, ctr_wrap_reg, &ctr_wrap_time);

        if (!delivered || !reference || !ref_perf) {
                ret = -EFAULT;
                goto out_err;
        }

        perf_fb_ctrs->delivered = delivered;
        perf_fb_ctrs->reference = reference;
        perf_fb_ctrs->reference_perf = ref_perf;
        perf_fb_ctrs->wraparound_time = ctr_wrap_time;
out_err:
        if (regs_in_pcc)
                up_write(&pcc_ss_data->pcc_lock);
        return ret;
}
EXPORT_SYMBOL_GPL(cppc_get_perf_ctrs);

/**
 * cppc_set_perf - Set a CPUs performance controls.
 * @cpu: CPU for which to set performance controls.
 * @perf_ctrls: ptr to cppc_perf_ctrls. See cppc_acpi.h
 *
 * Return: 0 for success, -ERRNO otherwise.
 */
int cppc_set_perf(int cpu, struct cppc_perf_ctrls *perf_ctrls)
{
        struct cpc_desc *cpc_desc = per_cpu(cpc_desc_ptr, cpu);
        struct cpc_register_resource *desired_reg;
        int pcc_ss_id = per_cpu(cpu_pcc_subspace_idx, cpu);
        struct cppc_pcc_data *pcc_ss_data;
        int ret = 0;

        if (!cpc_desc || pcc_ss_id < 0) {
                pr_debug("No CPC descriptor for CPU:%d\n", cpu);
                return -ENODEV;
        }

        pcc_ss_data = pcc_data[pcc_ss_id];
        desired_reg = &cpc_desc->cpc_regs[DESIRED_PERF];

        /*
         * This is Phase-I where we want to write to CPC registers
         * -> We want all CPUs to be able to execute this phase in parallel
         *
         * Since read_lock can be acquired by multiple CPUs simultaneously we
         * achieve that goal here
         */
        if (CPC_IN_PCC(desired_reg)) {
                down_read(&pcc_ss_data->pcc_lock); /* BEGIN Phase-I */
                if (pcc_ss_data->platform_owns_pcc) {
                        ret = check_pcc_chan(pcc_ss_id, false);
                        if (ret) {
                                up_read(&pcc_ss_data->pcc_lock);
                                return ret;
                        }
                }
                /*
                 * Update the pending_write to make sure a PCC CMD_READ will not
                 * arrive and steal the channel during the switch to write lock
                 */
                pcc_ss_data->pending_pcc_write_cmd = true;
                cpc_desc->write_cmd_id = pcc_ss_data->pcc_write_cnt;
                cpc_desc->write_cmd_status = 0;
        }

        /*
         * Skip writing MIN/MAX until Linux knows how to come up with
         * useful values.
         */
        cpc_write(cpu, desired_reg, perf_ctrls->desired_perf);

        if (CPC_IN_PCC(desired_reg))
                up_read(&pcc_ss_data->pcc_lock);        /* END Phase-I */
        /*
         * This is Phase-II where we transfer the ownership of PCC to Platform
         *
         * Short Summary: Basically if we think of a group of cppc_set_perf
         * requests that happened in short overlapping interval. The last CPU to
         * come out of Phase-I will enter Phase-II and ring the doorbell.
         *
         * We have the following requirements for Phase-II:
         *     1. We want to execute Phase-II only when there are no CPUs
         * currently executing in Phase-I
         *     2. Once we start Phase-II we want to avoid all other CPUs from
         * entering Phase-I.
         *     3. We want only one CPU among all those who went through Phase-I
         * to run phase-II
         *
         * If write_trylock fails to get the lock and doesn't transfer the
         * PCC ownership to the platform, then one of the following will be TRUE
         *     1. There is at-least one CPU in Phase-I which will later execute
         * write_trylock, so the CPUs in Phase-I will be responsible for
         * executing the Phase-II.
         *     2. Some other CPU has beaten this CPU to successfully execute the
         * write_trylock and has already acquired the write_lock. We know for a
         * fact it(other CPU acquiring the write_lock) couldn't have happened
         * before this CPU's Phase-I as we held the read_lock.
         *     3. Some other CPU executing pcc CMD_READ has stolen the
         * down_write, in which case, send_pcc_cmd will check for pending
         * CMD_WRITE commands by checking the pending_pcc_write_cmd.
         * So this CPU can be certain that its request will be delivered
         *    So in all cases, this CPU knows that its request will be delivered
         * by another CPU and can return
         *
         * After getting the down_write we still need to check for
         * pending_pcc_write_cmd to take care of the following scenario
         *    The thread running this code could be scheduled out between
         * Phase-I and Phase-II. Before it is scheduled back on, another CPU
         * could have delivered the request to Platform by triggering the
         * doorbell and transferred the ownership of PCC to platform. So this
         * avoids triggering an unnecessary doorbell and more importantly before
         * triggering the doorbell it makes sure that the PCC channel ownership
         * is still with OSPM.
         *   pending_pcc_write_cmd can also be cleared by a different CPU, if
         * there was a pcc CMD_READ waiting on down_write and it steals the lock
         * before the pcc CMD_WRITE is completed. pcc_send_cmd checks for this
         * case during a CMD_READ and if there are pending writes it delivers
         * the write command before servicing the read command
         */
        if (CPC_IN_PCC(desired_reg)) {
                if (down_write_trylock(&pcc_ss_data->pcc_lock)) {/* BEGIN Phase-II */
                        /* Update only if there are pending write commands */
                        if (pcc_ss_data->pending_pcc_write_cmd)
                                send_pcc_cmd(pcc_ss_id, CMD_WRITE);
                        up_write(&pcc_ss_data->pcc_lock);       /* END Phase-II */
                } else
                        /* Wait until pcc_write_cnt is updated by send_pcc_cmd */
                        wait_event(pcc_ss_data->pcc_write_wait_q,
                                   cpc_desc->write_cmd_id != pcc_ss_data->pcc_write_cnt);

                /* send_pcc_cmd updates the status in case of failure */
                ret = cpc_desc->write_cmd_status;
        }
        return ret;
}
EXPORT_SYMBOL_GPL(cppc_set_perf);

/**
 * cppc_get_transition_latency - returns frequency transition latency in ns
 *
 * ACPI CPPC does not explicitly specifiy how a platform can specify the
 * transition latency for perfromance change requests. The closest we have
 * is the timing information from the PCCT tables which provides the info
 * on the number and frequency of PCC commands the platform can handle.
 */
unsigned int cppc_get_transition_latency(int cpu_num)
{
        /*
         * Expected transition latency is based on the PCCT timing values
         * Below are definition from ACPI spec:
         * pcc_nominal- Expected latency to process a command, in microseconds
         * pcc_mpar   - The maximum number of periodic requests that the subspace
         *              channel can support, reported in commands per minute. 0
         *              indicates no limitation.
         * pcc_mrtt   - The minimum amount of time that OSPM must wait after the
         *              completion of a command before issuing the next command,
         *              in microseconds.
         */
        unsigned int latency_ns = 0;
        struct cpc_desc *cpc_desc;
        struct cpc_register_resource *desired_reg;
        int pcc_ss_id = per_cpu(cpu_pcc_subspace_idx, cpu_num);
        struct cppc_pcc_data *pcc_ss_data;

        cpc_desc = per_cpu(cpc_desc_ptr, cpu_num);
        if (!cpc_desc)
                return CPUFREQ_ETERNAL;

        desired_reg = &cpc_desc->cpc_regs[DESIRED_PERF];
        if (!CPC_IN_PCC(desired_reg))
                return CPUFREQ_ETERNAL;

        if (pcc_ss_id < 0)
                return CPUFREQ_ETERNAL;

        pcc_ss_data = pcc_data[pcc_ss_id];
        if (pcc_ss_data->pcc_mpar)
                latency_ns = 60 * (1000 * 1000 * 1000 / pcc_ss_data->pcc_mpar);

        latency_ns = max(latency_ns, pcc_ss_data->pcc_nominal * 1000);
        latency_ns = max(latency_ns, pcc_ss_data->pcc_mrtt * 1000);

        return latency_ns;
}
EXPORT_SYMBOL_GPL(cppc_get_transition_latency);