// SPDX-License-Identifier: GPL-2.0
/* Copyright (c) 2019, Vladimir Oltean <olteanv@gmail.com>
 */
#include "sja1105.h"

#define SJA1105_TAS_CLKSRC_DISABLED     0
#define SJA1105_TAS_CLKSRC_STANDALONE   1
#define SJA1105_TAS_CLKSRC_AS6802       2
#define SJA1105_TAS_CLKSRC_PTP          3
#define SJA1105_GATE_MASK               GENMASK_ULL(SJA1105_NUM_TC - 1, 0)

#define work_to_sja1105_tas(d) \
        container_of((d), struct sja1105_tas_data, tas_work)
#define tas_to_sja1105(d) \
        container_of((d), struct sja1105_private, tas_data)

static int sja1105_tas_set_runtime_params(struct sja1105_private *priv)
{
        struct sja1105_tas_data *tas_data = &priv->tas_data;
        struct sja1105_gating_config *gating_cfg = &tas_data->gating_cfg;
        struct dsa_switch *ds = priv->ds;
        s64 earliest_base_time = S64_MAX;
        s64 latest_base_time = 0;
        s64 its_cycle_time = 0;
        s64 max_cycle_time = 0;
        int port;

        tas_data->enabled = false;

        for (port = 0; port < ds->num_ports; port++) {
                const struct tc_taprio_qopt_offload *offload;

                offload = tas_data->offload[port];
                if (!offload)
                        continue;

                tas_data->enabled = true;

                if (max_cycle_time < offload->cycle_time)
                        max_cycle_time = offload->cycle_time;
                if (latest_base_time < offload->base_time)
                        latest_base_time = offload->base_time;
                if (earliest_base_time > offload->base_time) {
                        earliest_base_time = offload->base_time;
                        its_cycle_time = offload->cycle_time;
                }
        }

        if (!list_empty(&gating_cfg->entries)) {
                tas_data->enabled = true;

                if (max_cycle_time < gating_cfg->cycle_time)
                        max_cycle_time = gating_cfg->cycle_time;
                if (latest_base_time < gating_cfg->base_time)
                        latest_base_time = gating_cfg->base_time;
                if (earliest_base_time > gating_cfg->base_time) {
                        earliest_base_time = gating_cfg->base_time;
                        its_cycle_time = gating_cfg->cycle_time;
                }
        }

        if (!tas_data->enabled)
                return 0;

        /* Roll the earliest base time over until it is in a comparable
         * time base with the latest, then compare their deltas.
         * We want to enforce that all ports' base times are within
         * SJA1105_TAS_MAX_DELTA 200ns cycles of one another.
         */
        earliest_base_time = future_base_time(earliest_base_time,
                                              its_cycle_time,
                                              latest_base_time);
        while (earliest_base_time > latest_base_time)
                earliest_base_time -= its_cycle_time;
        if (latest_base_time - earliest_base_time >
            sja1105_delta_to_ns(SJA1105_TAS_MAX_DELTA)) {
                dev_err(ds->dev,
                        "Base times too far apart: min %llu max %llu\n",
                        earliest_base_time, latest_base_time);
                return -ERANGE;
        }

        tas_data->earliest_base_time = earliest_base_time;
        tas_data->max_cycle_time = max_cycle_time;

        dev_dbg(ds->dev, "earliest base time %lld ns\n", earliest_base_time);
        dev_dbg(ds->dev, "latest base time %lld ns\n", latest_base_time);
        dev_dbg(ds->dev, "longest cycle time %lld ns\n", max_cycle_time);

        return 0;
}

/* Lo and behold: the egress scheduler from hell.
 *
 * At the hardware level, the Time-Aware Shaper holds a global linear arrray of
 * all schedule entries for all ports. These are the Gate Control List (GCL)
 * entries, let's call them "timeslots" for short. This linear array of
 * timeslots is held in BLK_IDX_SCHEDULE.
 *
 * Then there are a maximum of 8 "execution threads" inside the switch, which
 * iterate cyclically through the "schedule". Each "cycle" has an entry point
 * and an exit point, both being timeslot indices in the schedule table. The
 * hardware calls each cycle a "subschedule".
 *
 * Subschedule (cycle) i starts when
 *   ptpclkval >= ptpschtm + BLK_IDX_SCHEDULE_ENTRY_POINTS[i].delta.
 *
 * The hardware scheduler iterates BLK_IDX_SCHEDULE with a k ranging from
 *   k = BLK_IDX_SCHEDULE_ENTRY_POINTS[i].address to
 *   k = BLK_IDX_SCHEDULE_PARAMS.subscheind[i]
 *
 * For each schedule entry (timeslot) k, the engine executes the gate control
 * list entry for the duration of BLK_IDX_SCHEDULE[k].delta.
 *
 *         +---------+
 *         |         | BLK_IDX_SCHEDULE_ENTRY_POINTS_PARAMS
 *         +---------+
 *              |
 *              +-----------------+
 *                                | .actsubsch
 *  BLK_IDX_SCHEDULE_ENTRY_POINTS v
 *                 +-------+-------+
 *                 |cycle 0|cycle 1|
 *                 +-------+-------+
 *                   |  |      |  |
 *  +----------------+  |      |  +-------------------------------------+
 *  |   .subschindx     |      |             .subschindx                |
 *  |                   |      +---------------+                        |
 *  |          .address |        .address      |                        |
 *  |                   |                      |                        |
 *  |                   |                      |                        |
 *  |  BLK_IDX_SCHEDULE v                      v                        |
 *  |              +-------+-------+-------+-------+-------+------+     |
 *  |              |entry 0|entry 1|entry 2|entry 3|entry 4|entry5|     |
 *  |              +-------+-------+-------+-------+-------+------+     |
 *  |                                  ^                    ^  ^  ^     |
 *  |                                  |                    |  |  |     |
 *  |        +-------------------------+                    |  |  |     |
 *  |        |              +-------------------------------+  |  |     |
 *  |        |              |              +-------------------+  |     |
 *  |        |              |              |                      |     |
 *  | +---------------------------------------------------------------+ |
 *  | |subscheind[0]<=subscheind[1]<=subscheind[2]<=...<=subscheind[7]| |
 *  | +---------------------------------------------------------------+ |
 *  |        ^              ^                BLK_IDX_SCHEDULE_PARAMS    |
 *  |        |              |                                           |
 *  +--------+              +-------------------------------------------+
 *
 *  In the above picture there are two subschedules (cycles):
 *
 *  - cycle 0: iterates the schedule table from 0 to 2 (and back)
 *  - cycle 1: iterates the schedule table from 3 to 5 (and back)
 *
 *  All other possible execution threads must be marked as unused by making
 *  their "subschedule end index" (subscheind) equal to the last valid
 *  subschedule's end index (in this case 5).
 */
int sja1105_init_scheduling(struct sja1105_private *priv)
{
        struct sja1105_schedule_entry_points_entry *schedule_entry_points;
        struct sja1105_schedule_entry_points_params_entry
                                        *schedule_entry_points_params;
        struct sja1105_schedule_params_entry *schedule_params;
        struct sja1105_tas_data *tas_data = &priv->tas_data;
        struct sja1105_gating_config *gating_cfg = &tas_data->gating_cfg;
        struct sja1105_schedule_entry *schedule;
        struct dsa_switch *ds = priv->ds;
        struct sja1105_table *table;
        int schedule_start_idx;
        s64 entry_point_delta;
        int schedule_end_idx;
        int num_entries = 0;
        int num_cycles = 0;
        int cycle = 0;
        int i, k = 0;
        int port, rc;

        rc = sja1105_tas_set_runtime_params(priv);
        if (rc < 0)
                return rc;

        /* Discard previous Schedule Table */
        table = &priv->static_config.tables[BLK_IDX_SCHEDULE];
        if (table->entry_count) {
                kfree(table->entries);
                table->entry_count = 0;
        }

        /* Discard previous Schedule Entry Points Parameters Table */
        table = &priv->static_config.tables[BLK_IDX_SCHEDULE_ENTRY_POINTS_PARAMS];
        if (table->entry_count) {
                kfree(table->entries);
                table->entry_count = 0;
        }

        /* Discard previous Schedule Parameters Table */
        table = &priv->static_config.tables[BLK_IDX_SCHEDULE_PARAMS];
        if (table->entry_count) {
                kfree(table->entries);
                table->entry_count = 0;
        }

        /* Discard previous Schedule Entry Points Table */
        table = &priv->static_config.tables[BLK_IDX_SCHEDULE_ENTRY_POINTS];
        if (table->entry_count) {
                kfree(table->entries);
                table->entry_count = 0;
        }

        /* Figure out the dimensioning of the problem */
        for (port = 0; port < ds->num_ports; port++) {
                if (tas_data->offload[port]) {
                        num_entries += tas_data->offload[port]->num_entries;
                        num_cycles++;
                }
        }

        if (!list_empty(&gating_cfg->entries)) {
                num_entries += gating_cfg->num_entries;
                num_cycles++;
        }

        /* Nothing to do */
        if (!num_cycles)
                return 0;

        /* Pre-allocate space in the static config tables */

        /* Schedule Table */
        table = &priv->static_config.tables[BLK_IDX_SCHEDULE];
        table->entries = kcalloc(num_entries, table->ops->unpacked_entry_size,
                                 GFP_KERNEL);
        if (!table->entries)
                return -ENOMEM;
        table->entry_count = num_entries;
        schedule = table->entries;

        /* Schedule Points Parameters Table */
        table = &priv->static_config.tables[BLK_IDX_SCHEDULE_ENTRY_POINTS_PARAMS];
        table->entries = kcalloc(SJA1105_MAX_SCHEDULE_ENTRY_POINTS_PARAMS_COUNT,
                                 table->ops->unpacked_entry_size, GFP_KERNEL);
        if (!table->entries)
                /* Previously allocated memory will be freed automatically in
                 * sja1105_static_config_free. This is true for all early
                 * returns below.
                 */
                return -ENOMEM;
        table->entry_count = SJA1105_MAX_SCHEDULE_ENTRY_POINTS_PARAMS_COUNT;
        schedule_entry_points_params = table->entries;

        /* Schedule Parameters Table */
        table = &priv->static_config.tables[BLK_IDX_SCHEDULE_PARAMS];
        table->entries = kcalloc(SJA1105_MAX_SCHEDULE_PARAMS_COUNT,
                                 table->ops->unpacked_entry_size, GFP_KERNEL);
        if (!table->entries)
                return -ENOMEM;
        table->entry_count = SJA1105_MAX_SCHEDULE_PARAMS_COUNT;
        schedule_params = table->entries;

        /* Schedule Entry Points Table */
        table = &priv->static_config.tables[BLK_IDX_SCHEDULE_ENTRY_POINTS];
        table->entries = kcalloc(num_cycles, table->ops->unpacked_entry_size,
                                 GFP_KERNEL);
        if (!table->entries)
                return -ENOMEM;
        table->entry_count = num_cycles;
        schedule_entry_points = table->entries;

        /* Finally start populating the static config tables */
        schedule_entry_points_params->clksrc = SJA1105_TAS_CLKSRC_PTP;
        schedule_entry_points_params->actsubsch = num_cycles - 1;

        for (port = 0; port < ds->num_ports; port++) {
                const struct tc_taprio_qopt_offload *offload;
                /* Relative base time */
                s64 rbt;

                offload = tas_data->offload[port];
                if (!offload)
                        continue;

                schedule_start_idx = k;
                schedule_end_idx = k + offload->num_entries - 1;
                /* This is the base time expressed as a number of TAS ticks
                 * relative to PTPSCHTM, which we'll (perhaps improperly) call
                 * the operational base time.
                 */
                rbt = future_base_time(offload->base_time,
                                       offload->cycle_time,
                                       tas_data->earliest_base_time);
                rbt -= tas_data->earliest_base_time;
                /* UM10944.pdf 4.2.2. Schedule Entry Points table says that
                 * delta cannot be zero, which is shitty. Advance all relative
                 * base times by 1 TAS delta, so that even the earliest base
                 * time becomes 1 in relative terms. Then start the operational
                 * base time (PTPSCHTM) one TAS delta earlier than planned.
                 */
                entry_point_delta = ns_to_sja1105_delta(rbt) + 1;

                schedule_entry_points[cycle].subschindx = cycle;
                schedule_entry_points[cycle].delta = entry_point_delta;
                schedule_entry_points[cycle].address = schedule_start_idx;

                /* The subschedule end indices need to be
                 * monotonically increasing.
                 */
                for (i = cycle; i < 8; i++)
                        schedule_params->subscheind[i] = schedule_end_idx;

                for (i = 0; i < offload->num_entries; i++, k++) {
                        s64 delta_ns = offload->entries[i].interval;

                        schedule[k].delta = ns_to_sja1105_delta(delta_ns);
                        schedule[k].destports = BIT(port);
                        schedule[k].resmedia_en = true;
                        schedule[k].resmedia = SJA1105_GATE_MASK &
                                        ~offload->entries[i].gate_mask;
                }
                cycle++;
        }

        if (!list_empty(&gating_cfg->entries)) {
                struct sja1105_gate_entry *e;

                /* Relative base time */
                s64 rbt;

                schedule_start_idx = k;
                schedule_end_idx = k + gating_cfg->num_entries - 1;
                rbt = future_base_time(gating_cfg->base_time,
                                       gating_cfg->cycle_time,
                                       tas_data->earliest_base_time);
                rbt -= tas_data->earliest_base_time;
                entry_point_delta = ns_to_sja1105_delta(rbt) + 1;

                schedule_entry_points[cycle].subschindx = cycle;
                schedule_entry_points[cycle].delta = entry_point_delta;
                schedule_entry_points[cycle].address = schedule_start_idx;

                for (i = cycle; i < 8; i++)
                        schedule_params->subscheind[i] = schedule_end_idx;

                list_for_each_entry(e, &gating_cfg->entries, list) {
                        schedule[k].delta = ns_to_sja1105_delta(e->interval);
                        schedule[k].destports = e->rule->vl.destports;
                        schedule[k].setvalid = true;
                        schedule[k].txen = true;
                        schedule[k].vlindex = e->rule->vl.sharindx;
                        schedule[k].winstindex = e->rule->vl.sharindx;
                        if (e->gate_state) /* Gate open */
                                schedule[k].winst = true;
                        else /* Gate closed */
                                schedule[k].winend = true;
                        k++;
                }
        }

        return 0;
}

/* Be there 2 port subschedules, each executing an arbitrary number of gate
 * open/close events cyclically.
 * None of those gate events must ever occur at the exact same time, otherwise
 * the switch is known to act in exotically strange ways.
 * However the hardware doesn't bother performing these integrity checks.
 * So here we are with the task of validating whether the new @admin offload
 * has any conflict with the already established TAS configuration in
 * tas_data->offload.  We already know the other ports are in harmony with one
 * another, otherwise we wouldn't have saved them.
 * Each gate event executes periodically, with a period of @cycle_time and a
 * phase given by its cycle's @base_time plus its offset within the cycle
 * (which in turn is given by the length of the events prior to it).
 * There are two aspects to possible collisions:
 * - Collisions within one cycle's (actually the longest cycle's) time frame.
 *   For that, we need to compare the cartesian product of each possible
 *   occurrence of each event within one cycle time.
 * - Collisions in the future. Events may not collide within one cycle time,
 *   but if two port schedules don't have the same periodicity (aka the cycle
 *   times aren't multiples of one another), they surely will some time in the
 *   future (actually they will collide an infinite amount of times).
 */
static bool
sja1105_tas_check_conflicts(struct sja1105_private *priv, int port,
                            const struct tc_taprio_qopt_offload *admin)
{
        struct sja1105_tas_data *tas_data = &priv->tas_data;
        const struct tc_taprio_qopt_offload *offload;
        s64 max_cycle_time, min_cycle_time;
        s64 delta1, delta2;
        s64 rbt1, rbt2;
        s64 stop_time;
        s64 t1, t2;
        int i, j;
        s32 rem;

        offload = tas_data->offload[port];
        if (!offload)
                return false;

        /* Check if the two cycle times are multiples of one another.
         * If they aren't, then they will surely collide.
         */
        max_cycle_time = max(offload->cycle_time, admin->cycle_time);
        min_cycle_time = min(offload->cycle_time, admin->cycle_time);
        div_s64_rem(max_cycle_time, min_cycle_time, &rem);
        if (rem)
                return true;

        /* Calculate the "reduced" base time of each of the two cycles
         * (transposed back as close to 0 as possible) by dividing to
         * the cycle time.
         */
        div_s64_rem(offload->base_time, offload->cycle_time, &rem);
        rbt1 = rem;

        div_s64_rem(admin->base_time, admin->cycle_time, &rem);
        rbt2 = rem;

        stop_time = max_cycle_time + max(rbt1, rbt2);

        /* delta1 is the relative base time of each GCL entry within
         * the established ports' TAS config.
         */
        for (i = 0, delta1 = 0;
             i < offload->num_entries;
             delta1 += offload->entries[i].interval, i++) {
                /* delta2 is the relative base time of each GCL entry
                 * within the newly added TAS config.
                 */
                for (j = 0, delta2 = 0;
                     j < admin->num_entries;
                     delta2 += admin->entries[j].interval, j++) {
                        /* t1 follows all possible occurrences of the
                         * established ports' GCL entry i within the
                         * first cycle time.
                         */
                        for (t1 = rbt1 + delta1;
                             t1 <= stop_time;
                             t1 += offload->cycle_time) {
                                /* t2 follows all possible occurrences
                                 * of the newly added GCL entry j
                                 * within the first cycle time.
                                 */
                                for (t2 = rbt2 + delta2;
                                     t2 <= stop_time;
                                     t2 += admin->cycle_time) {
                                        if (t1 == t2) {
                                                dev_warn(priv->ds->dev,
                                                         "GCL entry %d collides with entry %d of port %d\n",
                                                         j, i, port);
                                                return true;
                                        }
                                }
                        }
                }
        }

        return false;
}

/* Check the tc-taprio configuration on @port for conflicts with the tc-gate
 * global subschedule. If @port is -1, check it against all ports.
 * To reuse the sja1105_tas_check_conflicts logic without refactoring it,
 * convert the gating configuration to a dummy tc-taprio offload structure.
 */
bool sja1105_gating_check_conflicts(struct sja1105_private *priv, int port,
                                    struct netlink_ext_ack *extack)
{
        struct sja1105_gating_config *gating_cfg = &priv->tas_data.gating_cfg;
        size_t num_entries = gating_cfg->num_entries;
        struct tc_taprio_qopt_offload *dummy;
        struct dsa_switch *ds = priv->ds;
        struct sja1105_gate_entry *e;
        bool conflict;
        int i = 0;

        if (list_empty(&gating_cfg->entries))
                return false;

        dummy = kzalloc_flex(*dummy, entries, num_entries);
        if (!dummy) {
                NL_SET_ERR_MSG_MOD(extack, "Failed to allocate memory");
                return true;
        }

        dummy->num_entries = num_entries;
        dummy->base_time = gating_cfg->base_time;
        dummy->cycle_time = gating_cfg->cycle_time;

        list_for_each_entry(e, &gating_cfg->entries, list)
                dummy->entries[i++].interval = e->interval;

        if (port != -1) {
                conflict = sja1105_tas_check_conflicts(priv, port, dummy);
        } else {
                for (port = 0; port < ds->num_ports; port++) {
                        conflict = sja1105_tas_check_conflicts(priv, port,
                                                               dummy);
                        if (conflict)
                                break;
                }
        }

        kfree(dummy);

        return conflict;
}

int sja1105_setup_tc_taprio(struct dsa_switch *ds, int port,
                            struct tc_taprio_qopt_offload *admin)
{
        struct sja1105_private *priv = ds->priv;
        struct sja1105_tas_data *tas_data = &priv->tas_data;
        int other_port, rc, i;

        /* Can't change an already configured port (must delete qdisc first).
         * Can't delete the qdisc from an unconfigured port.
         */
        if ((!!tas_data->offload[port] && admin->cmd == TAPRIO_CMD_REPLACE) ||
            (!tas_data->offload[port] && admin->cmd == TAPRIO_CMD_DESTROY))
                return -EINVAL;

        if (admin->cmd == TAPRIO_CMD_DESTROY) {
                taprio_offload_free(tas_data->offload[port]);
                tas_data->offload[port] = NULL;

                rc = sja1105_init_scheduling(priv);
                if (rc < 0)
                        return rc;

                return sja1105_static_config_reload(priv, SJA1105_SCHEDULING);
        } else if (admin->cmd != TAPRIO_CMD_REPLACE) {
                return -EOPNOTSUPP;
        }

        /* The cycle time extension is the amount of time the last cycle from
         * the old OPER needs to be extended in order to phase-align with the
         * base time of the ADMIN when that becomes the new OPER.
         * But of course our switch needs to be reset to switch-over between
         * the ADMIN and the OPER configs - so much for a seamless transition.
         * So don't add insult over injury and just say we don't support cycle
         * time extension.
         */
        if (admin->cycle_time_extension)
                return -ENOTSUPP;

        for (i = 0; i < admin->num_entries; i++) {
                s64 delta_ns = admin->entries[i].interval;
                s64 delta_cycles = ns_to_sja1105_delta(delta_ns);
                bool too_long, too_short;

                too_long = (delta_cycles >= SJA1105_TAS_MAX_DELTA);
                too_short = (delta_cycles == 0);
                if (too_long || too_short) {
                        dev_err(priv->ds->dev,
                                "Interval %llu too %s for GCL entry %d\n",
                                delta_ns, too_long ? "long" : "short", i);
                        return -ERANGE;
                }
        }

        for (other_port = 0; other_port < ds->num_ports; other_port++) {
                if (other_port == port)
                        continue;

                if (sja1105_tas_check_conflicts(priv, other_port, admin))
                        return -ERANGE;
        }

        if (sja1105_gating_check_conflicts(priv, port, NULL)) {
                dev_err(ds->dev, "Conflict with tc-gate schedule\n");
                return -ERANGE;
        }

        tas_data->offload[port] = taprio_offload_get(admin);

        rc = sja1105_init_scheduling(priv);
        if (rc < 0)
                return rc;

        return sja1105_static_config_reload(priv, SJA1105_SCHEDULING);
}

static int sja1105_tas_check_running(struct sja1105_private *priv)
{
        struct sja1105_tas_data *tas_data = &priv->tas_data;
        struct dsa_switch *ds = priv->ds;
        struct sja1105_ptp_cmd cmd = {0};
        int rc;

        rc = sja1105_ptp_commit(ds, &cmd, SPI_READ);
        if (rc < 0)
                return rc;

        if (cmd.ptpstrtsch == 1)
                /* Schedule successfully started */
                tas_data->state = SJA1105_TAS_STATE_RUNNING;
        else if (cmd.ptpstopsch == 1)
                /* Schedule is stopped */
                tas_data->state = SJA1105_TAS_STATE_DISABLED;
        else
                /* Schedule is probably not configured with PTP clock source */
                rc = -EINVAL;

        return rc;
}

/* Write to PTPCLKCORP */
static int sja1105_tas_adjust_drift(struct sja1105_private *priv,
                                    u64 correction)
{
        const struct sja1105_regs *regs = priv->info->regs;
        u32 ptpclkcorp = ns_to_sja1105_ticks(correction);

        return sja1105_xfer_u32(priv, SPI_WRITE, regs->ptpclkcorp,
                                &ptpclkcorp, NULL);
}

/* Write to PTPSCHTM */
static int sja1105_tas_set_base_time(struct sja1105_private *priv,
                                     u64 base_time)
{
        const struct sja1105_regs *regs = priv->info->regs;
        u64 ptpschtm = ns_to_sja1105_ticks(base_time);

        return sja1105_xfer_u64(priv, SPI_WRITE, regs->ptpschtm,
                                &ptpschtm, NULL);
}

static int sja1105_tas_start(struct sja1105_private *priv)
{
        struct sja1105_tas_data *tas_data = &priv->tas_data;
        struct sja1105_ptp_cmd *cmd = &priv->ptp_data.cmd;
        struct dsa_switch *ds = priv->ds;
        int rc;

        dev_dbg(ds->dev, "Starting the TAS\n");

        if (tas_data->state == SJA1105_TAS_STATE_ENABLED_NOT_RUNNING ||
            tas_data->state == SJA1105_TAS_STATE_RUNNING) {
                dev_err(ds->dev, "TAS already started\n");
                return -EINVAL;
        }

        cmd->ptpstrtsch = 1;
        cmd->ptpstopsch = 0;

        rc = sja1105_ptp_commit(ds, cmd, SPI_WRITE);
        if (rc < 0)
                return rc;

        tas_data->state = SJA1105_TAS_STATE_ENABLED_NOT_RUNNING;

        return 0;
}

static int sja1105_tas_stop(struct sja1105_private *priv)
{
        struct sja1105_tas_data *tas_data = &priv->tas_data;
        struct sja1105_ptp_cmd *cmd = &priv->ptp_data.cmd;
        struct dsa_switch *ds = priv->ds;
        int rc;

        dev_dbg(ds->dev, "Stopping the TAS\n");

        if (tas_data->state == SJA1105_TAS_STATE_DISABLED) {
                dev_err(ds->dev, "TAS already disabled\n");
                return -EINVAL;
        }

        cmd->ptpstopsch = 1;
        cmd->ptpstrtsch = 0;

        rc = sja1105_ptp_commit(ds, cmd, SPI_WRITE);
        if (rc < 0)
                return rc;

        tas_data->state = SJA1105_TAS_STATE_DISABLED;

        return 0;
}

/* The schedule engine and the PTP clock are driven by the same oscillator, and
 * they run in parallel. But whilst the PTP clock can keep an absolute
 * time-of-day, the schedule engine is only running in 'ticks' (25 ticks make
 * up a delta, which is 200ns), and wrapping around at the end of each cycle.
 * The schedule engine is started when the PTP clock reaches the PTPSCHTM time
 * (in PTP domain).
 * Because the PTP clock can be rate-corrected (accelerated or slowed down) by
 * a software servo, and the schedule engine clock runs in parallel to the PTP
 * clock, there is logic internal to the switch that periodically keeps the
 * schedule engine from drifting away. The frequency with which this internal
 * syntonization happens is the PTP clock correction period (PTPCLKCORP). It is
 * a value also in the PTP clock domain, and is also rate-corrected.
 * To be precise, during a correction period, there is logic to determine by
 * how many scheduler clock ticks has the PTP clock drifted. At the end of each
 * correction period/beginning of new one, the length of a delta is shrunk or
 * expanded with an integer number of ticks, compared with the typical 25.
 * So a delta lasts for 200ns (or 25 ticks) only on average.
 * Sometimes it is longer, sometimes it is shorter. The internal syntonization
 * logic can adjust for at most 5 ticks each 20 ticks.
 *
 * The first implication is that you should choose your schedule correction
 * period to be an integer multiple of the schedule length. Preferably one.
 * In case there are schedules of multiple ports active, then the correction
 * period needs to be a multiple of them all. Given the restriction that the
 * cycle times have to be multiples of one another anyway, this means the
 * correction period can simply be the largest cycle time, hence the current
 * choice. This way, the updates are always synchronous to the transmission
 * cycle, and therefore predictable.
 *
 * The second implication is that at the beginning of a correction period, the
 * first few deltas will be modulated in time, until the schedule engine is
 * properly phase-aligned with the PTP clock. For this reason, you should place
 * your best-effort traffic at the beginning of a cycle, and your
 * time-triggered traffic afterwards.
 *
 * The third implication is that once the schedule engine is started, it can
 * only adjust for so much drift within a correction period. In the servo you
 * can only change the PTPCLKRATE, but not step the clock (PTPCLKADD). If you
 * want to do the latter, you need to stop and restart the schedule engine,
 * which is what the state machine handles.
 */
static void sja1105_tas_state_machine(struct work_struct *work)
{
        struct sja1105_tas_data *tas_data = work_to_sja1105_tas(work);
        struct sja1105_private *priv = tas_to_sja1105(tas_data);
        struct sja1105_ptp_data *ptp_data = &priv->ptp_data;
        struct timespec64 base_time_ts, now_ts;
        struct dsa_switch *ds = priv->ds;
        struct timespec64 diff;
        s64 base_time, now;
        int rc = 0;

        mutex_lock(&ptp_data->lock);

        switch (tas_data->state) {
        case SJA1105_TAS_STATE_DISABLED:
                /* Can't do anything at all if clock is still being stepped */
                if (tas_data->last_op != SJA1105_PTP_ADJUSTFREQ)
                        break;

                rc = sja1105_tas_adjust_drift(priv, tas_data->max_cycle_time);
                if (rc < 0)
                        break;

                rc = __sja1105_ptp_gettimex(ds, &now, NULL);
                if (rc < 0)
                        break;

                /* Plan to start the earliest schedule first. The others
                 * will be started in hardware, by way of their respective
                 * entry points delta.
                 * Try our best to avoid fringe cases (race condition between
                 * ptpschtm and ptpstrtsch) by pushing the oper_base_time at
                 * least one second in the future from now. This is not ideal,
                 * but this only needs to buy us time until the
                 * sja1105_tas_start command below gets executed.
                 */
                base_time = future_base_time(tas_data->earliest_base_time,
                                             tas_data->max_cycle_time,
                                             now + 1ull * NSEC_PER_SEC);
                base_time -= sja1105_delta_to_ns(1);

                rc = sja1105_tas_set_base_time(priv, base_time);
                if (rc < 0)
                        break;

                tas_data->oper_base_time = base_time;

                rc = sja1105_tas_start(priv);
                if (rc < 0)
                        break;

                base_time_ts = ns_to_timespec64(base_time);
                now_ts = ns_to_timespec64(now);

                dev_dbg(ds->dev, "OPER base time %ptSp (now %ptSp)\n",
                        &base_time_ts, &now_ts);

                break;

        case SJA1105_TAS_STATE_ENABLED_NOT_RUNNING:
                if (tas_data->last_op != SJA1105_PTP_ADJUSTFREQ) {
                        /* Clock was stepped.. bad news for TAS */
                        sja1105_tas_stop(priv);
                        break;
                }

                /* Check if TAS has actually started, by comparing the
                 * scheduled start time with the SJA1105 PTP clock
                 */
                rc = __sja1105_ptp_gettimex(ds, &now, NULL);
                if (rc < 0)
                        break;

                if (now < tas_data->oper_base_time) {
                        /* TAS has not started yet */
                        diff = ns_to_timespec64(tas_data->oper_base_time - now);
                        dev_dbg(ds->dev, "time to start: [%ptSp]", &diff);
                        break;
                }

                /* Time elapsed, what happened? */
                rc = sja1105_tas_check_running(priv);
                if (rc < 0)
                        break;

                if (tas_data->state != SJA1105_TAS_STATE_RUNNING)
                        /* TAS has started */
                        dev_err(ds->dev,
                                "TAS not started despite time elapsed\n");

                break;

        case SJA1105_TAS_STATE_RUNNING:
                /* Clock was stepped.. bad news for TAS */
                if (tas_data->last_op != SJA1105_PTP_ADJUSTFREQ) {
                        sja1105_tas_stop(priv);
                        break;
                }

                rc = sja1105_tas_check_running(priv);
                if (rc < 0)
                        break;

                if (tas_data->state != SJA1105_TAS_STATE_RUNNING)
                        dev_err(ds->dev, "TAS surprisingly stopped\n");

                break;

        default:
                if (net_ratelimit())
                        dev_err(ds->dev, "TAS in an invalid state (incorrect use of API)!\n");
        }

        if (rc && net_ratelimit())
                dev_err(ds->dev, "An operation returned %d\n", rc);

        mutex_unlock(&ptp_data->lock);
}

void sja1105_tas_clockstep(struct dsa_switch *ds)
{
        struct sja1105_private *priv = ds->priv;
        struct sja1105_tas_data *tas_data = &priv->tas_data;

        if (!tas_data->enabled)
                return;

        tas_data->last_op = SJA1105_PTP_CLOCKSTEP;
        schedule_work(&tas_data->tas_work);
}

void sja1105_tas_adjfreq(struct dsa_switch *ds)
{
        struct sja1105_private *priv = ds->priv;
        struct sja1105_tas_data *tas_data = &priv->tas_data;

        if (!tas_data->enabled)
                return;

        /* No reason to schedule the workqueue, nothing changed */
        if (tas_data->state == SJA1105_TAS_STATE_RUNNING)
                return;

        tas_data->last_op = SJA1105_PTP_ADJUSTFREQ;
        schedule_work(&tas_data->tas_work);
}

void sja1105_tas_setup(struct dsa_switch *ds)
{
        struct sja1105_private *priv = ds->priv;
        struct sja1105_tas_data *tas_data = &priv->tas_data;

        INIT_WORK(&tas_data->tas_work, sja1105_tas_state_machine);
        tas_data->state = SJA1105_TAS_STATE_DISABLED;
        tas_data->last_op = SJA1105_PTP_NONE;

        INIT_LIST_HEAD(&tas_data->gating_cfg.entries);
}

void sja1105_tas_teardown(struct dsa_switch *ds)
{
        struct sja1105_private *priv = ds->priv;
        struct tc_taprio_qopt_offload *offload;
        int port;

        cancel_work_sync(&priv->tas_data.tas_work);

        for (port = 0; port < ds->num_ports; port++) {
                offload = priv->tas_data.offload[port];
                if (!offload)
                        continue;

                taprio_offload_free(offload);
        }
}