/*
 * Copyright 2007, Mattias Nissler <mattias.nissler@gmx.de>
 * Copyright 2007, Stefano Brivio <stefano.brivio@polimi.it>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 */

#ifndef RC80211_PID_H
#define RC80211_PID_H

/* Sampling period for measuring percentage of failed frames in ms. */
#define RC_PID_INTERVAL                 125

/* Exponential averaging smoothness (used for I part of PID controller) */
#define RC_PID_SMOOTHING_SHIFT          3
#define RC_PID_SMOOTHING                (1 << RC_PID_SMOOTHING_SHIFT)

/* Sharpening factor (used for D part of PID controller) */
#define RC_PID_SHARPENING_FACTOR        0
#define RC_PID_SHARPENING_DURATION      0

/* Fixed point arithmetic shifting amount. */
#define RC_PID_ARITH_SHIFT              8

/* Fixed point arithmetic factor. */
#define RC_PID_ARITH_FACTOR             (1 << RC_PID_ARITH_SHIFT)

/* Proportional PID component coefficient. */
#define RC_PID_COEFF_P                  15
/* Integral PID component coefficient. */
#define RC_PID_COEFF_I                  9
/* Derivative PID component coefficient. */
#define RC_PID_COEFF_D                  15

/* Target failed frames rate for the PID controller. NB: This effectively gives
 * maximum failed frames percentage we're willing to accept. If the wireless
 * link quality is good, the controller will fail to adjust failed frames
 * percentage to the target. This is intentional.
 */
#define RC_PID_TARGET_PF                14

/* Rate behaviour normalization quantity over time. */
#define RC_PID_NORM_OFFSET              3

/* Push high rates right after loading. */
#define RC_PID_FAST_START               0

/* Arithmetic right shift for positive and negative values for ISO C. */
#define RC_PID_DO_ARITH_RIGHT_SHIFT(x, y) \
        ((x) < 0 ? -((-(x)) >> (y)) : (x) >> (y))

enum rc_pid_event_type {
        RC_PID_EVENT_TYPE_TX_STATUS,
        RC_PID_EVENT_TYPE_RATE_CHANGE,
        RC_PID_EVENT_TYPE_TX_RATE,
        RC_PID_EVENT_TYPE_PF_SAMPLE,
};

union rc_pid_event_data {
        /* RC_PID_EVENT_TX_STATUS */
        struct {
                u32 flags;
                struct ieee80211_tx_info tx_status;
        };
        /* RC_PID_EVENT_TYPE_RATE_CHANGE */
        /* RC_PID_EVENT_TYPE_TX_RATE */
        struct {
                int index;
                int rate;
        };
        /* RC_PID_EVENT_TYPE_PF_SAMPLE */
        struct {
                s32 pf_sample;
                s32 prop_err;
                s32 int_err;
                s32 der_err;
        };
};

struct rc_pid_event {
        /* The time when the event occured */
        unsigned long timestamp;

        /* Event ID number */
        unsigned int id;

        /* Type of event */
        enum rc_pid_event_type type;

        /* type specific data */
        union rc_pid_event_data data;
};

/* Size of the event ring buffer. */
#define RC_PID_EVENT_RING_SIZE 32

struct rc_pid_event_buffer {
        /* Counter that generates event IDs */
        unsigned int ev_count;

        /* Ring buffer of events */
        struct rc_pid_event ring[RC_PID_EVENT_RING_SIZE];

        /* Index to the entry in events_buf to be reused */
        unsigned int next_entry;

        /* Lock that guards against concurrent access to this buffer struct */
        spinlock_t lock;

        /* Wait queue for poll/select and blocking I/O */
        wait_queue_head_t waitqueue;
};

struct rc_pid_events_file_info {
        /* The event buffer we read */
        struct rc_pid_event_buffer *events;

        /* The entry we have should read next */
        unsigned int next_entry;
};

/**
 * struct rc_pid_debugfs_entries - tunable parameters
 *
 * Algorithm parameters, tunable via debugfs.
 * @target: target percentage for failed frames
 * @sampling_period: error sampling interval in milliseconds
 * @coeff_p: absolute value of the proportional coefficient
 * @coeff_i: absolute value of the integral coefficient
 * @coeff_d: absolute value of the derivative coefficient
 * @smoothing_shift: absolute value of the integral smoothing factor (i.e.
 *      amount of smoothing introduced by the exponential moving average)
 * @sharpen_factor: absolute value of the derivative sharpening factor (i.e.
 *      amount of emphasis given to the derivative term after low activity
 *      events)
 * @sharpen_duration: duration of the sharpening effect after the detected low
 *      activity event, relative to sampling_period
 * @norm_offset: amount of normalization periodically performed on the learnt
 *      rate behaviour values (lower means we should trust more what we learnt
 *      about behaviour of rates, higher means we should trust more the natural
 *      ordering of rates)
 */
struct rc_pid_debugfs_entries {
        struct dentry *target;
        struct dentry *sampling_period;
        struct dentry *coeff_p;
        struct dentry *coeff_i;
        struct dentry *coeff_d;
        struct dentry *smoothing_shift;
        struct dentry *sharpen_factor;
        struct dentry *sharpen_duration;
        struct dentry *norm_offset;
};

void rate_control_pid_event_tx_status(struct rc_pid_event_buffer *buf,
                                      struct ieee80211_tx_info *stat);

void rate_control_pid_event_rate_change(struct rc_pid_event_buffer *buf,
                                               int index, int rate);

void rate_control_pid_event_tx_rate(struct rc_pid_event_buffer *buf,
                                           int index, int rate);

void rate_control_pid_event_pf_sample(struct rc_pid_event_buffer *buf,
                                             s32 pf_sample, s32 prop_err,
                                             s32 int_err, s32 der_err);

void rate_control_pid_add_sta_debugfs(void *priv, void *priv_sta,
                                             struct dentry *dir);

void rate_control_pid_remove_sta_debugfs(void *priv, void *priv_sta);

struct rc_pid_sta_info {
        unsigned long last_change;
        unsigned long last_sample;

        u32 tx_num_failed;
        u32 tx_num_xmit;

        int txrate_idx;

        /* Average failed frames percentage error (i.e. actual vs. target
         * percentage), scaled by RC_PID_SMOOTHING. This value is computed
         * using using an exponential weighted average technique:
         *
         *           (RC_PID_SMOOTHING - 1) * err_avg_old + err
         * err_avg = ------------------------------------------
         *                       RC_PID_SMOOTHING
         *
         * where err_avg is the new approximation, err_avg_old the previous one
         * and err is the error w.r.t. to the current failed frames percentage
         * sample. Note that the bigger RC_PID_SMOOTHING the more weight is
         * given to the previous estimate, resulting in smoother behavior (i.e.
         * corresponding to a longer integration window).
         *
         * For computation, we actually don't use the above formula, but this
         * one:
         *
         * err_avg_scaled = err_avg_old_scaled - err_avg_old + err
         *
         * where:
         *      err_avg_scaled = err * RC_PID_SMOOTHING
         *      err_avg_old_scaled = err_avg_old * RC_PID_SMOOTHING
         *
         * This avoids floating point numbers and the per_failed_old value can
         * easily be obtained by shifting per_failed_old_scaled right by
         * RC_PID_SMOOTHING_SHIFT.
         */
        s32 err_avg_sc;

        /* Last framed failes percentage sample. */
        u32 last_pf;

        /* Sharpening needed. */
        u8 sharp_cnt;

#ifdef CONFIG_MAC80211_DEBUGFS
        /* Event buffer */
        struct rc_pid_event_buffer events;

        /* Events debugfs file entry */
        struct dentry *events_entry;
#endif
};

/* Algorithm parameters. We keep them on a per-algorithm approach, so they can
 * be tuned individually for each interface.
 */
struct rc_pid_rateinfo {

        /* Map sorted rates to rates in ieee80211_hw_mode. */
        int index;

        /* Map rates in ieee80211_hw_mode to sorted rates. */
        int rev_index;

        /* Did we do any measurement on this rate? */
        bool valid;

        /* Comparison with the lowest rate. */
        int diff;
};

struct rc_pid_info {

        /* The failed frames percentage target. */
        unsigned int target;

        /* Rate at which failed frames percentage is sampled in 0.001s. */
        unsigned int sampling_period;

        /* P, I and D coefficients. */
        int coeff_p;
        int coeff_i;
        int coeff_d;

        /* Exponential averaging shift. */
        unsigned int smoothing_shift;

        /* Sharpening factor and duration. */
        unsigned int sharpen_factor;
        unsigned int sharpen_duration;

        /* Normalization offset. */
        unsigned int norm_offset;

        /* Rates information. */
        struct rc_pid_rateinfo *rinfo;

        /* Index of the last used rate. */
        int oldrate;

#ifdef CONFIG_MAC80211_DEBUGFS
        /* Debugfs entries created for the parameters above. */
        struct rc_pid_debugfs_entries dentries;
#endif
};

#endif /* RC80211_PID_H */