// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * PowerNV OPAL asynchronous completion interfaces
 *
 * Copyright 2013-2017 IBM Corp.
 */

#undef DEBUG

#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/slab.h>
#include <linux/sched.h>
#include <linux/semaphore.h>
#include <linux/spinlock.h>
#include <linux/wait.h>
#include <linux/gfp.h>
#include <linux/of.h>
#include <asm/machdep.h>
#include <asm/opal.h>

enum opal_async_token_state {
        ASYNC_TOKEN_UNALLOCATED = 0,
        ASYNC_TOKEN_ALLOCATED,
        ASYNC_TOKEN_DISPATCHED,
        ASYNC_TOKEN_ABANDONED,
        ASYNC_TOKEN_COMPLETED
};

struct opal_async_token {
        enum opal_async_token_state state;
        struct opal_msg response;
};

static DECLARE_WAIT_QUEUE_HEAD(opal_async_wait);
static DEFINE_SPINLOCK(opal_async_comp_lock);
static struct semaphore opal_async_sem;
static unsigned int opal_max_async_tokens;
static struct opal_async_token *opal_async_tokens;

static int __opal_async_get_token(void)
{
        unsigned long flags;
        int i, token = -EBUSY;

        spin_lock_irqsave(&opal_async_comp_lock, flags);

        for (i = 0; i < opal_max_async_tokens; i++) {
                if (opal_async_tokens[i].state == ASYNC_TOKEN_UNALLOCATED) {
                        opal_async_tokens[i].state = ASYNC_TOKEN_ALLOCATED;
                        token = i;
                        break;
                }
        }

        spin_unlock_irqrestore(&opal_async_comp_lock, flags);
        return token;
}

/*
 * Note: If the returned token is used in an opal call and opal returns
 * OPAL_ASYNC_COMPLETION you MUST call one of opal_async_wait_response() or
 * opal_async_wait_response_interruptible() at least once before calling another
 * opal_async_* function
 */
int opal_async_get_token_interruptible(void)
{
        int token;

        /* Wait until a token is available */
        if (down_interruptible(&opal_async_sem))
                return -ERESTARTSYS;

        token = __opal_async_get_token();
        if (token < 0)
                up(&opal_async_sem);

        return token;
}
EXPORT_SYMBOL_GPL(opal_async_get_token_interruptible);

static int __opal_async_release_token(int token)
{
        unsigned long flags;
        int rc;

        if (token < 0 || token >= opal_max_async_tokens) {
                pr_err("%s: Passed token is out of range, token %d\n",
                                __func__, token);
                return -EINVAL;
        }

        spin_lock_irqsave(&opal_async_comp_lock, flags);
        switch (opal_async_tokens[token].state) {
        case ASYNC_TOKEN_COMPLETED:
        case ASYNC_TOKEN_ALLOCATED:
                opal_async_tokens[token].state = ASYNC_TOKEN_UNALLOCATED;
                rc = 0;
                break;
        /*
         * DISPATCHED and ABANDONED tokens must wait for OPAL to respond.
         * Mark a DISPATCHED token as ABANDONED so that the response handling
         * code knows no one cares and that it can free it then.
         */
        case ASYNC_TOKEN_DISPATCHED:
                opal_async_tokens[token].state = ASYNC_TOKEN_ABANDONED;
                fallthrough;
        default:
                rc = 1;
        }
        spin_unlock_irqrestore(&opal_async_comp_lock, flags);

        return rc;
}

int opal_async_release_token(int token)
{
        int ret;

        ret = __opal_async_release_token(token);
        if (!ret)
                up(&opal_async_sem);

        return ret;
}
EXPORT_SYMBOL_GPL(opal_async_release_token);

int opal_async_wait_response(uint64_t token, struct opal_msg *msg)
{
        if (token >= opal_max_async_tokens) {
                pr_err("%s: Invalid token passed\n", __func__);
                return -EINVAL;
        }

        if (!msg) {
                pr_err("%s: Invalid message pointer passed\n", __func__);
                return -EINVAL;
        }

        /*
         * There is no need to mark the token as dispatched, wait_event()
         * will block until the token completes.
         *
         * Wakeup the poller before we wait for events to speed things
         * up on platforms or simulators where the interrupts aren't
         * functional.
         */
        opal_wake_poller();
        wait_event(opal_async_wait, opal_async_tokens[token].state
                        == ASYNC_TOKEN_COMPLETED);
        memcpy(msg, &opal_async_tokens[token].response, sizeof(*msg));

        return 0;
}
EXPORT_SYMBOL_GPL(opal_async_wait_response);

int opal_async_wait_response_interruptible(uint64_t token, struct opal_msg *msg)
{
        unsigned long flags;
        int ret;

        if (token >= opal_max_async_tokens) {
                pr_err("%s: Invalid token passed\n", __func__);
                return -EINVAL;
        }

        if (!msg) {
                pr_err("%s: Invalid message pointer passed\n", __func__);
                return -EINVAL;
        }

        /*
         * The first time this gets called we mark the token as DISPATCHED
         * so that if wait_event_interruptible() returns not zero and the
         * caller frees the token, we know not to actually free the token
         * until the response comes.
         *
         * Only change if the token is ALLOCATED - it may have been
         * completed even before the caller gets around to calling this
         * the first time.
         *
         * There is also a dirty great comment at the token allocation
         * function that if the opal call returns OPAL_ASYNC_COMPLETION to
         * the caller then the caller *must* call this or the not
         * interruptible version before doing anything else with the
         * token.
         */
        if (opal_async_tokens[token].state == ASYNC_TOKEN_ALLOCATED) {
                spin_lock_irqsave(&opal_async_comp_lock, flags);
                if (opal_async_tokens[token].state == ASYNC_TOKEN_ALLOCATED)
                        opal_async_tokens[token].state = ASYNC_TOKEN_DISPATCHED;
                spin_unlock_irqrestore(&opal_async_comp_lock, flags);
        }

        /*
         * Wakeup the poller before we wait for events to speed things
         * up on platforms or simulators where the interrupts aren't
         * functional.
         */
        opal_wake_poller();
        ret = wait_event_interruptible(opal_async_wait,
                        opal_async_tokens[token].state ==
                        ASYNC_TOKEN_COMPLETED);
        if (!ret)
                memcpy(msg, &opal_async_tokens[token].response, sizeof(*msg));

        return ret;
}
EXPORT_SYMBOL_GPL(opal_async_wait_response_interruptible);

/* Called from interrupt context */
static int opal_async_comp_event(struct notifier_block *nb,
                unsigned long msg_type, void *msg)
{
        struct opal_msg *comp_msg = msg;
        enum opal_async_token_state state;
        unsigned long flags;
        uint64_t token;

        if (msg_type != OPAL_MSG_ASYNC_COMP)
                return 0;

        token = be64_to_cpu(comp_msg->params[0]);
        spin_lock_irqsave(&opal_async_comp_lock, flags);
        state = opal_async_tokens[token].state;
        opal_async_tokens[token].state = ASYNC_TOKEN_COMPLETED;
        spin_unlock_irqrestore(&opal_async_comp_lock, flags);

        if (state == ASYNC_TOKEN_ABANDONED) {
                /* Free the token, no one else will */
                opal_async_release_token(token);
                return 0;
        }
        memcpy(&opal_async_tokens[token].response, comp_msg, sizeof(*comp_msg));
        wake_up(&opal_async_wait);

        return 0;
}

static struct notifier_block opal_async_comp_nb = {
                .notifier_call  = opal_async_comp_event,
                .next           = NULL,
                .priority       = 0,
};

int __init opal_async_comp_init(void)
{
        struct device_node *opal_node;
        const __be32 *async;
        int err;

        opal_node = of_find_node_by_path("/ibm,opal");
        if (!opal_node) {
                pr_err("%s: Opal node not found\n", __func__);
                err = -ENOENT;
                goto out;
        }

        async = of_get_property(opal_node, "opal-msg-async-num", NULL);
        if (!async) {
                pr_err("%s: %pOF has no opal-msg-async-num\n",
                                __func__, opal_node);
                err = -ENOENT;
                goto out_opal_node;
        }

        opal_max_async_tokens = be32_to_cpup(async);
        opal_async_tokens = kcalloc(opal_max_async_tokens,
                        sizeof(*opal_async_tokens), GFP_KERNEL);
        if (!opal_async_tokens) {
                err = -ENOMEM;
                goto out_opal_node;
        }

        err = opal_message_notifier_register(OPAL_MSG_ASYNC_COMP,
                        &opal_async_comp_nb);
        if (err) {
                pr_err("%s: Can't register OPAL event notifier (%d)\n",
                                __func__, err);
                kfree(opal_async_tokens);
                goto out_opal_node;
        }

        sema_init(&opal_async_sem, opal_max_async_tokens);

out_opal_node:
        of_node_put(opal_node);
out:
        return err;
}