/*
 * net/sched/sch_cbs.c  Credit Based Shaper
 *
 *              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; either version
 *              2 of the License, or (at your option) any later version.
 *
 * Authors:     Vinicius Costa Gomes <vinicius.gomes@intel.com>
 *
 */

/* Credit Based Shaper (CBS)
 * =========================
 *
 * This is a simple rate-limiting shaper aimed at TSN applications on
 * systems with known traffic workloads.
 *
 * Its algorithm is defined by the IEEE 802.1Q-2014 Specification,
 * Section 8.6.8.2, and explained in more detail in the Annex L of the
 * same specification.
 *
 * There are four tunables to be considered:
 *
 *      'idleslope': Idleslope is the rate of credits that is
 *      accumulated (in kilobits per second) when there is at least
 *      one packet waiting for transmission. Packets are transmitted
 *      when the current value of credits is equal or greater than
 *      zero. When there is no packet to be transmitted the amount of
 *      credits is set to zero. This is the main tunable of the CBS
 *      algorithm.
 *
 *      'sendslope':
 *      Sendslope is the rate of credits that is depleted (it should be a
 *      negative number of kilobits per second) when a transmission is
 *      ocurring. It can be calculated as follows, (IEEE 802.1Q-2014 Section
 *      8.6.8.2 item g):
 *
 *      sendslope = idleslope - port_transmit_rate
 *
 *      'hicredit': Hicredit defines the maximum amount of credits (in
 *      bytes) that can be accumulated. Hicredit depends on the
 *      characteristics of interfering traffic,
 *      'max_interference_size' is the maximum size of any burst of
 *      traffic that can delay the transmission of a frame that is
 *      available for transmission for this traffic class, (IEEE
 *      802.1Q-2014 Annex L, Equation L-3):
 *
 *      hicredit = max_interference_size * (idleslope / port_transmit_rate)
 *
 *      'locredit': Locredit is the minimum amount of credits that can
 *      be reached. It is a function of the traffic flowing through
 *      this qdisc (IEEE 802.1Q-2014 Annex L, Equation L-2):
 *
 *      locredit = max_frame_size * (sendslope / port_transmit_rate)
 */

#include <linux/module.h>
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/string.h>
#include <linux/errno.h>
#include <linux/skbuff.h>
#include <net/netlink.h>
#include <net/sch_generic.h>
#include <net/pkt_sched.h>

#define BYTES_PER_KBIT (1000LL / 8)

struct cbs_sched_data {
        bool offload;
        int queue;
        s64 port_rate; /* in bytes/s */
        s64 last; /* timestamp in ns */
        s64 credits; /* in bytes */
        s32 locredit; /* in bytes */
        s32 hicredit; /* in bytes */
        s64 sendslope; /* in bytes/s */
        s64 idleslope; /* in bytes/s */
        struct qdisc_watchdog watchdog;
        int (*enqueue)(struct sk_buff *skb, struct Qdisc *sch);
        struct sk_buff *(*dequeue)(struct Qdisc *sch);
};

static int cbs_enqueue_offload(struct sk_buff *skb, struct Qdisc *sch)
{
        return qdisc_enqueue_tail(skb, sch);
}

static int cbs_enqueue_soft(struct sk_buff *skb, struct Qdisc *sch)
{
        struct cbs_sched_data *q = qdisc_priv(sch);

        if (sch->q.qlen == 0 && q->credits > 0) {
                /* We need to stop accumulating credits when there's
                 * no enqueued packets and q->credits is positive.
                 */
                q->credits = 0;
                q->last = ktime_get_ns();
        }

        return qdisc_enqueue_tail(skb, sch);
}

static int cbs_enqueue(struct sk_buff *skb, struct Qdisc *sch,
                       struct sk_buff **to_free)
{
        struct cbs_sched_data *q = qdisc_priv(sch);

        return q->enqueue(skb, sch);
}

/* timediff is in ns, slope is in bytes/s */
static s64 timediff_to_credits(s64 timediff, s64 slope)
{
        return div64_s64(timediff * slope, NSEC_PER_SEC);
}

static s64 delay_from_credits(s64 credits, s64 slope)
{
        if (unlikely(slope == 0))
                return S64_MAX;

        return div64_s64(-credits * NSEC_PER_SEC, slope);
}

static s64 credits_from_len(unsigned int len, s64 slope, s64 port_rate)
{
        if (unlikely(port_rate == 0))
                return S64_MAX;

        return div64_s64(len * slope, port_rate);
}

static struct sk_buff *cbs_dequeue_soft(struct Qdisc *sch)
{
        struct cbs_sched_data *q = qdisc_priv(sch);
        s64 now = ktime_get_ns();
        struct sk_buff *skb;
        s64 credits;
        int len;

        if (q->credits < 0) {
                credits = timediff_to_credits(now - q->last, q->idleslope);

                credits = q->credits + credits;
                q->credits = min_t(s64, credits, q->hicredit);

                if (q->credits < 0) {
                        s64 delay;

                        delay = delay_from_credits(q->credits, q->idleslope);
                        qdisc_watchdog_schedule_ns(&q->watchdog, now + delay);

                        q->last = now;

                        return NULL;
                }
        }

        skb = qdisc_dequeue_head(sch);
        if (!skb)
                return NULL;

        len = qdisc_pkt_len(skb);

        /* As sendslope is a negative number, this will decrease the
         * amount of q->credits.
         */
        credits = credits_from_len(len, q->sendslope, q->port_rate);
        credits += q->credits;

        q->credits = max_t(s64, credits, q->locredit);
        q->last = now;

        return skb;
}

static struct sk_buff *cbs_dequeue_offload(struct Qdisc *sch)
{
        return qdisc_dequeue_head(sch);
}

static struct sk_buff *cbs_dequeue(struct Qdisc *sch)
{
        struct cbs_sched_data *q = qdisc_priv(sch);

        return q->dequeue(sch);
}

static const struct nla_policy cbs_policy[TCA_CBS_MAX + 1] = {
        [TCA_CBS_PARMS] = { .len = sizeof(struct tc_cbs_qopt) },
};

static void cbs_disable_offload(struct net_device *dev,
                                struct cbs_sched_data *q)
{
        struct tc_cbs_qopt_offload cbs = { };
        const struct net_device_ops *ops;
        int err;

        if (!q->offload)
                return;

        q->enqueue = cbs_enqueue_soft;
        q->dequeue = cbs_dequeue_soft;

        ops = dev->netdev_ops;
        if (!__rh_has_ndo_setup_tc(dev))
                return;

        cbs.queue = q->queue;
        cbs.enable = 0;

        err = __rh_call_ndo_setup_tc(dev, 0, TC_SETUP_QDISC_CBS, &cbs);
        if (err < 0)
                pr_warn("Couldn't disable CBS offload for queue %d\n",
                        cbs.queue);
}

static int cbs_enable_offload(struct net_device *dev, struct cbs_sched_data *q,
                              const struct tc_cbs_qopt *opt)
{
        const struct net_device_ops *ops __maybe_unused = dev->netdev_ops;
        struct tc_cbs_qopt_offload cbs = { };
        int err;

        if (!__rh_has_ndo_setup_tc(dev))
                return -EOPNOTSUPP;

        cbs.queue = q->queue;

        cbs.enable = 1;
        cbs.hicredit = opt->hicredit;
        cbs.locredit = opt->locredit;
        cbs.idleslope = opt->idleslope;
        cbs.sendslope = opt->sendslope;

        err = __rh_call_ndo_setup_tc(dev, 0, TC_SETUP_QDISC_CBS, &cbs);
        if (err < 0)
                return err;

        q->enqueue = cbs_enqueue_offload;
        q->dequeue = cbs_dequeue_offload;

        return 0;
}

static int cbs_change(struct Qdisc *sch, struct nlattr *opt)
{
        struct cbs_sched_data *q = qdisc_priv(sch);
        struct net_device *dev = qdisc_dev(sch);
        struct nlattr *tb[TCA_CBS_MAX + 1];
        struct tc_cbs_qopt *qopt;
        int err;

        err = nla_parse_nested(tb, TCA_CBS_MAX, opt, cbs_policy);
        if (err < 0)
                return err;

        if (!tb[TCA_CBS_PARMS])
                return -EINVAL;

        qopt = nla_data(tb[TCA_CBS_PARMS]);

        if (!qopt->offload) {
                struct ethtool_link_ksettings ecmd;
                s64 link_speed;

                if (!__ethtool_get_link_ksettings(dev, &ecmd))
                        link_speed = ecmd.base.speed;
                else
                        link_speed = SPEED_1000;

                q->port_rate = link_speed * 1000 * BYTES_PER_KBIT;

                cbs_disable_offload(dev, q);
        } else {
                err = cbs_enable_offload(dev, q, qopt);
                if (err < 0)
                        return err;
        }

        /* Everything went OK, save the parameters used. */
        q->hicredit = qopt->hicredit;
        q->locredit = qopt->locredit;
        q->idleslope = qopt->idleslope * BYTES_PER_KBIT;
        q->sendslope = qopt->sendslope * BYTES_PER_KBIT;
        q->offload = qopt->offload;

        return 0;
}

static int cbs_init(struct Qdisc *sch, struct nlattr *opt)
{
        struct cbs_sched_data *q = qdisc_priv(sch);
        struct net_device *dev = qdisc_dev(sch);

        if (!opt)
                return -EINVAL;

        q->queue = sch->dev_queue - netdev_get_tx_queue(dev, 0);

        q->enqueue = cbs_enqueue_soft;
        q->dequeue = cbs_dequeue_soft;

        qdisc_watchdog_init(&q->watchdog, sch);

        return cbs_change(sch, opt);
}

static void cbs_destroy(struct Qdisc *sch)
{
        struct cbs_sched_data *q = qdisc_priv(sch);
        struct net_device *dev = qdisc_dev(sch);

        /*
         * RHEL: don't try further uninit if qdisc_watchdog_init()
         * and cbs_change() have not been called.
         */
        if (!q->watchdog.qdisc)
                return;

        qdisc_watchdog_cancel(&q->watchdog);

        cbs_disable_offload(dev, q);
}

static int cbs_dump(struct Qdisc *sch, struct sk_buff *skb)
{
        struct cbs_sched_data *q = qdisc_priv(sch);
        struct tc_cbs_qopt opt = { };
        struct nlattr *nest;

        nest = nla_nest_start(skb, TCA_OPTIONS);
        if (!nest)
                goto nla_put_failure;

        opt.hicredit = q->hicredit;
        opt.locredit = q->locredit;
        opt.sendslope = div64_s64(q->sendslope, BYTES_PER_KBIT);
        opt.idleslope = div64_s64(q->idleslope, BYTES_PER_KBIT);
        opt.offload = q->offload;

        if (nla_put(skb, TCA_CBS_PARMS, sizeof(opt), &opt))
                goto nla_put_failure;

        return nla_nest_end(skb, nest);

nla_put_failure:
        nla_nest_cancel(skb, nest);
        return -1;
}

static struct Qdisc_ops cbs_qdisc_ops __read_mostly = {
        .id             =       "cbs",
        .priv_size      =       sizeof(struct cbs_sched_data),
        .enqueue        =       cbs_enqueue,
        .dequeue        =       cbs_dequeue,
        .peek           =       qdisc_peek_dequeued,
        .init           =       cbs_init,
        .reset          =       qdisc_reset_queue,
        .destroy        =       cbs_destroy,
        .change         =       cbs_change,
        .dump           =       cbs_dump,
        .owner          =       THIS_MODULE,
};

static int __init cbs_module_init(void)
{
        return register_qdisc(&cbs_qdisc_ops);
}

static void __exit cbs_module_exit(void)
{
        unregister_qdisc(&cbs_qdisc_ops);
}
module_init(cbs_module_init)
module_exit(cbs_module_exit)
MODULE_LICENSE("GPL");