// SPDX-License-Identifier: GPL-2.0-or-later
/*
 *      LAPB release 002
 *
 *      This code REQUIRES 2.1.15 or higher/ NET3.038
 *
 *      History
 *      LAPB 001        Jonathan Naylor Started Coding
 *      LAPB 002        Jonathan Naylor New timer architecture.
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/errno.h>
#include <linux/types.h>
#include <linux/socket.h>
#include <linux/in.h>
#include <linux/kernel.h>
#include <linux/timer.h>
#include <linux/string.h>
#include <linux/sockios.h>
#include <linux/net.h>
#include <linux/inet.h>
#include <linux/skbuff.h>
#include <linux/slab.h>
#include <net/sock.h>
#include <linux/uaccess.h>
#include <linux/fcntl.h>
#include <linux/mm.h>
#include <linux/interrupt.h>
#include <net/lapb.h>

/*
 *  This procedure is passed a buffer descriptor for an iframe. It builds
 *  the rest of the control part of the frame and then writes it out.
 */
static void lapb_send_iframe(struct lapb_cb *lapb, struct sk_buff *skb, int poll_bit)
{
        unsigned char *frame;

        if (!skb)
                return;

        if (lapb->mode & LAPB_EXTENDED) {
                frame = skb_push(skb, 2);

                frame[0] = LAPB_I;
                frame[0] |= lapb->vs << 1;
                frame[1] = poll_bit ? LAPB_EPF : 0;
                frame[1] |= lapb->vr << 1;
        } else {
                frame = skb_push(skb, 1);

                *frame = LAPB_I;
                *frame |= poll_bit ? LAPB_SPF : 0;
                *frame |= lapb->vr << 5;
                *frame |= lapb->vs << 1;
        }

        lapb_dbg(1, "(%p) S%d TX I(%d) S%d R%d\n",
                 lapb->dev, lapb->state, poll_bit, lapb->vs, lapb->vr);

        lapb_transmit_buffer(lapb, skb, LAPB_COMMAND);
}

void lapb_kick(struct lapb_cb *lapb)
{
        struct sk_buff *skb, *skbn;
        unsigned short modulus, start, end;

        modulus = (lapb->mode & LAPB_EXTENDED) ? LAPB_EMODULUS : LAPB_SMODULUS;
        start = !skb_peek(&lapb->ack_queue) ? lapb->va : lapb->vs;
        end   = (lapb->va + lapb->window) % modulus;

        if (!(lapb->condition & LAPB_PEER_RX_BUSY_CONDITION) &&
            start != end && skb_peek(&lapb->write_queue)) {
                lapb->vs = start;

                /*
                 * Dequeue the frame and copy it.
                 */
                skb = skb_dequeue(&lapb->write_queue);

                do {
                        if ((skbn = skb_clone(skb, GFP_ATOMIC)) == NULL) {
                                skb_queue_head(&lapb->write_queue, skb);
                                break;
                        }

                        if (skb->sk)
                                skb_set_owner_w(skbn, skb->sk);

                        /*
                         * Transmit the frame copy.
                         */
                        lapb_send_iframe(lapb, skbn, LAPB_POLLOFF);

                        lapb->vs = (lapb->vs + 1) % modulus;

                        /*
                         * Requeue the original data frame.
                         */
                        skb_queue_tail(&lapb->ack_queue, skb);

                } while (lapb->vs != end && (skb = skb_dequeue(&lapb->write_queue)) != NULL);

                lapb->condition &= ~LAPB_ACK_PENDING_CONDITION;

                if (!lapb_t1timer_running(lapb))
                        lapb_start_t1timer(lapb);
        }
}

void lapb_transmit_buffer(struct lapb_cb *lapb, struct sk_buff *skb, int type)
{
        unsigned char *ptr;

        ptr = skb_push(skb, 1);

        if (lapb->mode & LAPB_MLP) {
                if (lapb->mode & LAPB_DCE) {
                        if (type == LAPB_COMMAND)
                                *ptr = LAPB_ADDR_C;
                        if (type == LAPB_RESPONSE)
                                *ptr = LAPB_ADDR_D;
                } else {
                        if (type == LAPB_COMMAND)
                                *ptr = LAPB_ADDR_D;
                        if (type == LAPB_RESPONSE)
                                *ptr = LAPB_ADDR_C;
                }
        } else {
                if (lapb->mode & LAPB_DCE) {
                        if (type == LAPB_COMMAND)
                                *ptr = LAPB_ADDR_A;
                        if (type == LAPB_RESPONSE)
                                *ptr = LAPB_ADDR_B;
                } else {
                        if (type == LAPB_COMMAND)
                                *ptr = LAPB_ADDR_B;
                        if (type == LAPB_RESPONSE)
                                *ptr = LAPB_ADDR_A;
                }
        }

        lapb_dbg(2, "(%p) S%d TX %3ph\n", lapb->dev, lapb->state, skb->data);

        if (!lapb_data_transmit(lapb, skb))
                kfree_skb(skb);
}

void lapb_establish_data_link(struct lapb_cb *lapb)
{
        lapb->condition = 0x00;
        lapb->n2count   = 0;

        if (lapb->mode & LAPB_EXTENDED) {
                lapb_dbg(1, "(%p) S%d TX SABME(1)\n", lapb->dev, lapb->state);
                lapb_send_control(lapb, LAPB_SABME, LAPB_POLLON, LAPB_COMMAND);
        } else {
                lapb_dbg(1, "(%p) S%d TX SABM(1)\n", lapb->dev, lapb->state);
                lapb_send_control(lapb, LAPB_SABM, LAPB_POLLON, LAPB_COMMAND);
        }

        lapb_start_t1timer(lapb);
        lapb_stop_t2timer(lapb);
}

void lapb_enquiry_response(struct lapb_cb *lapb)
{
        lapb_dbg(1, "(%p) S%d TX RR(1) R%d\n",
                 lapb->dev, lapb->state, lapb->vr);

        lapb_send_control(lapb, LAPB_RR, LAPB_POLLON, LAPB_RESPONSE);

        lapb->condition &= ~LAPB_ACK_PENDING_CONDITION;
}

void lapb_timeout_response(struct lapb_cb *lapb)
{
        lapb_dbg(1, "(%p) S%d TX RR(0) R%d\n",
                 lapb->dev, lapb->state, lapb->vr);
        lapb_send_control(lapb, LAPB_RR, LAPB_POLLOFF, LAPB_RESPONSE);

        lapb->condition &= ~LAPB_ACK_PENDING_CONDITION;
}

void lapb_check_iframes_acked(struct lapb_cb *lapb, unsigned short nr)
{
        if (lapb->vs == nr) {
                lapb_frames_acked(lapb, nr);
                lapb_stop_t1timer(lapb);
                lapb->n2count = 0;
        } else if (lapb->va != nr) {
                lapb_frames_acked(lapb, nr);
                lapb_start_t1timer(lapb);
        }
}

void lapb_check_need_response(struct lapb_cb *lapb, int type, int pf)
{
        if (type == LAPB_COMMAND && pf)
                lapb_enquiry_response(lapb);
}