/*
 * Xen event channels (FIFO-based ABI)
 *
 * Copyright (C) 2013 Citrix Systems R&D ltd.
 *
 * This source code 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; either version 2 of the
 * License, or (at your option) any later version.
 *
 * Or, when distributed separately from the Linux kernel or
 * incorporated into other software packages, subject to the following
 * license:
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this source file (the "Software"), to deal in the Software without
 * restriction, including without limitation the rights to use, copy, modify,
 * merge, publish, distribute, sublicense, and/or sell copies of the Software,
 * and to permit persons to whom the Software is furnished to do so, subject to
 * the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
 * IN THE SOFTWARE.
 */

#define pr_fmt(fmt) "xen:" KBUILD_MODNAME ": " fmt

#include <linux/linkage.h>
#include <linux/interrupt.h>
#include <linux/irq.h>
#include <linux/smp.h>
#include <linux/percpu.h>
#include <linux/cpu.h>

#include <asm/barrier.h>
#include <asm/sync_bitops.h>
#include <asm/xen/hypercall.h>
#include <asm/xen/hypervisor.h>

#include <xen/xen.h>
#include <xen/xen-ops.h>
#include <xen/events.h>
#include <xen/interface/xen.h>
#include <xen/interface/event_channel.h>
#include <xen/page.h>

#include "events_internal.h"

#define EVENT_WORDS_PER_PAGE (XEN_PAGE_SIZE / sizeof(event_word_t))
#define MAX_EVENT_ARRAY_PAGES (EVTCHN_FIFO_NR_CHANNELS / EVENT_WORDS_PER_PAGE)

struct evtchn_fifo_queue {
        uint32_t head[EVTCHN_FIFO_MAX_QUEUES];
};

static DEFINE_PER_CPU(struct evtchn_fifo_control_block *, cpu_control_block);
static DEFINE_PER_CPU(struct evtchn_fifo_queue, cpu_queue);
static event_word_t *event_array[MAX_EVENT_ARRAY_PAGES] __read_mostly;
static unsigned event_array_pages __read_mostly;

/*
 * sync_set_bit() and friends must be unsigned long aligned.
 */
#if BITS_PER_LONG > 32

#define BM(w) (unsigned long *)((unsigned long)w & ~0x7UL)
#define EVTCHN_FIFO_BIT(b, w) \
    (((unsigned long)w & 0x4UL) ? (EVTCHN_FIFO_ ##b + 32) : EVTCHN_FIFO_ ##b)

#else

#define BM(w) ((unsigned long *)(w))
#define EVTCHN_FIFO_BIT(b, w) EVTCHN_FIFO_ ##b

#endif

static inline event_word_t *event_word_from_port(evtchn_port_t port)
{
        unsigned i = port / EVENT_WORDS_PER_PAGE;

        return event_array[i] + port % EVENT_WORDS_PER_PAGE;
}

static unsigned evtchn_fifo_max_channels(void)
{
        return EVTCHN_FIFO_NR_CHANNELS;
}

static unsigned evtchn_fifo_nr_channels(void)
{
        return event_array_pages * EVENT_WORDS_PER_PAGE;
}

static int init_control_block(int cpu,
                              struct evtchn_fifo_control_block *control_block)
{
        struct evtchn_fifo_queue *q = &per_cpu(cpu_queue, cpu);
        struct evtchn_init_control init_control;
        unsigned int i;

        /* Reset the control block and the local HEADs. */
        clear_page(control_block);
        for (i = 0; i < EVTCHN_FIFO_MAX_QUEUES; i++)
                q->head[i] = 0;

        init_control.control_gfn = virt_to_gfn(control_block);
        init_control.offset      = 0;
        init_control.vcpu        = xen_vcpu_nr(cpu);

        return HYPERVISOR_event_channel_op(EVTCHNOP_init_control, &init_control);
}

static void free_unused_array_pages(void)
{
        unsigned i;

        for (i = event_array_pages; i < MAX_EVENT_ARRAY_PAGES; i++) {
                if (!event_array[i])
                        break;
                free_page((unsigned long)event_array[i]);
                event_array[i] = NULL;
        }
}

static void init_array_page(event_word_t *array_page)
{
        unsigned i;

        for (i = 0; i < EVENT_WORDS_PER_PAGE; i++)
                array_page[i] = 1 << EVTCHN_FIFO_MASKED;
}

static int evtchn_fifo_setup(evtchn_port_t port)
{
        unsigned new_array_pages;
        int ret;

        new_array_pages = port / EVENT_WORDS_PER_PAGE + 1;

        if (new_array_pages > MAX_EVENT_ARRAY_PAGES)
                return -EINVAL;

        while (event_array_pages < new_array_pages) {
                void *array_page;
                struct evtchn_expand_array expand_array;

                /* Might already have a page if we've resumed. */
                array_page = event_array[event_array_pages];
                if (!array_page) {
                        array_page = (void *)__get_free_page(GFP_KERNEL);
                        if (array_page == NULL) {
                                ret = -ENOMEM;
                                goto error;
                        }
                        event_array[event_array_pages] = array_page;
                }

                /* Mask all events in this page before adding it. */
                init_array_page(array_page);

                expand_array.array_gfn = virt_to_gfn(array_page);

                ret = HYPERVISOR_event_channel_op(EVTCHNOP_expand_array, &expand_array);
                if (ret < 0)
                        goto error;

                event_array_pages++;
        }
        return 0;

  error:
        if (event_array_pages == 0)
                panic("xen: unable to expand event array with initial page (%d)\n", ret);
        else
                pr_err("unable to expand event array (%d)\n", ret);
        free_unused_array_pages();
        return ret;
}

static void evtchn_fifo_bind_to_cpu(evtchn_port_t evtchn, unsigned int cpu, 
                                    unsigned int old_cpu)
{
        /* no-op */
}

static void evtchn_fifo_clear_pending(evtchn_port_t port)
{
        event_word_t *word = event_word_from_port(port);
        sync_clear_bit(EVTCHN_FIFO_BIT(PENDING, word), BM(word));
}

static void evtchn_fifo_set_pending(evtchn_port_t port)
{
        event_word_t *word = event_word_from_port(port);
        sync_set_bit(EVTCHN_FIFO_BIT(PENDING, word), BM(word));
}

static bool evtchn_fifo_is_pending(evtchn_port_t port)
{
        event_word_t *word = event_word_from_port(port);
        return sync_test_bit(EVTCHN_FIFO_BIT(PENDING, word), BM(word));
}

static void evtchn_fifo_mask(evtchn_port_t port)
{
        event_word_t *word = event_word_from_port(port);
        sync_set_bit(EVTCHN_FIFO_BIT(MASKED, word), BM(word));
}

static bool evtchn_fifo_is_masked(evtchn_port_t port)
{
        event_word_t *word = event_word_from_port(port);
        return sync_test_bit(EVTCHN_FIFO_BIT(MASKED, word), BM(word));
}
/*
 * Clear MASKED if not PENDING, spinning if BUSY is set.
 * Return true if mask was cleared.
 */
static bool clear_masked_cond(volatile event_word_t *word)
{
        event_word_t new, old, w;

        w = *word;

        do {
                if (!(w & (1 << EVTCHN_FIFO_MASKED)))
                        return true;

                if (w & (1 << EVTCHN_FIFO_PENDING))
                        return false;

                old = w & ~(1 << EVTCHN_FIFO_BUSY);
                new = old & ~(1 << EVTCHN_FIFO_MASKED);
                w = sync_cmpxchg(word, old, new);
        } while (w != old);

        return true;
}

static void evtchn_fifo_unmask(evtchn_port_t port)
{
        event_word_t *word = event_word_from_port(port);

        BUG_ON(!irqs_disabled());

        if (!clear_masked_cond(word)) {
                struct evtchn_unmask unmask = { .port = port };
                (void)HYPERVISOR_event_channel_op(EVTCHNOP_unmask, &unmask);
        }
}

static uint32_t clear_linked(volatile event_word_t *word)
{
        event_word_t new, old, w;

        w = *word;

        do {
                old = w;
                new = (w & ~((1 << EVTCHN_FIFO_LINKED)
                             | EVTCHN_FIFO_LINK_MASK));
        } while ((w = sync_cmpxchg(word, old, new)) != old);

        return w & EVTCHN_FIFO_LINK_MASK;
}

static void consume_one_event(unsigned cpu, struct evtchn_loop_ctrl *ctrl,
                              struct evtchn_fifo_control_block *control_block,
                              unsigned priority, unsigned long *ready)
{
        struct evtchn_fifo_queue *q = &per_cpu(cpu_queue, cpu);
        uint32_t head;
        evtchn_port_t port;
        event_word_t *word;

        head = q->head[priority];

        /*
         * Reached the tail last time?  Read the new HEAD from the
         * control block.
         */
        if (head == 0) {
                virt_rmb(); /* Ensure word is up-to-date before reading head. */
                head = control_block->head[priority];
        }

        port = head;
        word = event_word_from_port(port);
        head = clear_linked(word);

        /*
         * If the link is non-zero, there are more events in the
         * queue, otherwise the queue is empty.
         *
         * If the queue is empty, clear this priority from our local
         * copy of the ready word.
         */
        if (head == 0)
                clear_bit(priority, ready);

        if (evtchn_fifo_is_pending(port) && !evtchn_fifo_is_masked(port)) {
                if (unlikely(!ctrl))
                        pr_warn("Dropping pending event for port %u\n", port);
                else
                        handle_irq_for_port(port, ctrl);
        }

        q->head[priority] = head;
}

static void __evtchn_fifo_handle_events(unsigned cpu,
                                        struct evtchn_loop_ctrl *ctrl)
{
        struct evtchn_fifo_control_block *control_block;
        unsigned long ready;
        unsigned q;

        control_block = per_cpu(cpu_control_block, cpu);

        ready = xchg(&control_block->ready, 0);

        while (ready) {
                q = find_first_bit(&ready, EVTCHN_FIFO_MAX_QUEUES);
                consume_one_event(cpu, ctrl, control_block, q, &ready);
                ready |= xchg(&control_block->ready, 0);
        }
}

static void evtchn_fifo_handle_events(unsigned cpu,
                                      struct evtchn_loop_ctrl *ctrl)
{
        __evtchn_fifo_handle_events(cpu, ctrl);
}

static void evtchn_fifo_resume(void)
{
        unsigned cpu;

        for_each_possible_cpu(cpu) {
                void *control_block = per_cpu(cpu_control_block, cpu);
                int ret;

                if (!control_block)
                        continue;

                /*
                 * If this CPU is offline, take the opportunity to
                 * free the control block while it is not being
                 * used.
                 */
                if (!cpu_online(cpu)) {
                        free_page((unsigned long)control_block);
                        per_cpu(cpu_control_block, cpu) = NULL;
                        continue;
                }

                ret = init_control_block(cpu, control_block);
                BUG_ON(ret < 0);
        }

        /*
         * The event array starts out as empty again and is extended
         * as normal when events are bound.  The existing pages will
         * be reused.
         */
        event_array_pages = 0;
}

static int evtchn_fifo_alloc_control_block(unsigned cpu)
{
        void *control_block = NULL;
        int ret = -ENOMEM;

        control_block = (void *)__get_free_page(GFP_KERNEL);
        if (control_block == NULL)
                goto error;

        ret = init_control_block(cpu, control_block);
        if (ret < 0)
                goto error;

        per_cpu(cpu_control_block, cpu) = control_block;

        return 0;

  error:
        free_page((unsigned long)control_block);
        return ret;
}

static int evtchn_fifo_percpu_init(unsigned int cpu)
{
        if (!per_cpu(cpu_control_block, cpu))
                return evtchn_fifo_alloc_control_block(cpu);
        return 0;
}

static int evtchn_fifo_percpu_deinit(unsigned int cpu)
{
        __evtchn_fifo_handle_events(cpu, NULL);
        return 0;
}

static const struct evtchn_ops evtchn_ops_fifo = {
        .max_channels      = evtchn_fifo_max_channels,
        .nr_channels       = evtchn_fifo_nr_channels,
        .setup             = evtchn_fifo_setup,
        .bind_to_cpu       = evtchn_fifo_bind_to_cpu,
        .clear_pending     = evtchn_fifo_clear_pending,
        .set_pending       = evtchn_fifo_set_pending,
        .is_pending        = evtchn_fifo_is_pending,
        .mask              = evtchn_fifo_mask,
        .unmask            = evtchn_fifo_unmask,
        .handle_events     = evtchn_fifo_handle_events,
        .resume            = evtchn_fifo_resume,
        .percpu_init       = evtchn_fifo_percpu_init,
        .percpu_deinit     = evtchn_fifo_percpu_deinit,
};

int __init xen_evtchn_fifo_init(void)
{
        int cpu = smp_processor_id();
        int ret;

        ret = evtchn_fifo_alloc_control_block(cpu);
        if (ret < 0)
                return ret;

        pr_info("Using FIFO-based ABI\n");

        evtchn_ops = &evtchn_ops_fifo;

        return ret;
}