/*
 * Common data handling layer for ser_gigaset and usb_gigaset
 *
 * Copyright (c) 2005 by Tilman Schmidt <tilman@imap.cc>,
 *                       Hansjoerg Lipp <hjlipp@web.de>,
 *                       Stefan Eilers.
 *
 * =====================================================================
 *      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.
 * =====================================================================
 */

#include "gigaset.h"
#include <linux/crc-ccitt.h>
#include <linux/bitrev.h>
#include <linux/export.h>

/* check if byte must be stuffed/escaped
 * I'm not sure which data should be encoded.
 * Therefore I will go the hard way and encode every value
 * less than 0x20, the flag sequence and the control escape char.
 */
static inline int muststuff(unsigned char c)
{
        if (c < PPP_TRANS) return 1;
        if (c == PPP_FLAG) return 1;
        if (c == PPP_ESCAPE) return 1;
        /* other possible candidates: */
        /* 0x91: XON with parity set */
        /* 0x93: XOFF with parity set */
        return 0;
}

/* == data input =========================================================== */

/* process a block of received bytes in command mode
 * (mstate != MS_LOCKED && (inputstate & INS_command))
 * Append received bytes to the command response buffer and forward them
 * line by line to the response handler. Exit whenever a mode/state change
 * might have occurred.
 * Note: Received lines may be terminated by CR, LF, or CR LF, which will be
 * removed before passing the line to the response handler.
 * Return value:
 *      number of processed bytes
 */
static unsigned cmd_loop(unsigned numbytes, struct inbuf_t *inbuf)
{
        unsigned char *src = inbuf->data + inbuf->head;
        struct cardstate *cs = inbuf->cs;
        unsigned cbytes = cs->cbytes;
        unsigned procbytes = 0;
        unsigned char c;

        while (procbytes < numbytes) {
                c = *src++;
                procbytes++;

                switch (c) {
                case '\n':
                        if (cbytes == 0 && cs->respdata[0] == '\r') {
                                /* collapse LF with preceding CR */
                                cs->respdata[0] = 0;
                                break;
                        }
                        /* --v-- fall through --v-- */
                case '\r':
                        /* end of message line, pass to response handler */
                        if (cbytes >= MAX_RESP_SIZE) {
                                dev_warn(cs->dev, "response too large (%d)\n",
                                         cbytes);
                                cbytes = MAX_RESP_SIZE;
                        }
                        cs->cbytes = cbytes;
                        gigaset_dbg_buffer(DEBUG_TRANSCMD, "received response",
                                           cbytes, cs->respdata);
                        gigaset_handle_modem_response(cs);
                        cbytes = 0;

                        /* store EOL byte for CRLF collapsing */
                        cs->respdata[0] = c;

                        /* cs->dle may have changed */
                        if (cs->dle && !(inbuf->inputstate & INS_DLE_command))
                                inbuf->inputstate &= ~INS_command;

                        /* return for reevaluating state */
                        goto exit;

                case DLE_FLAG:
                        if (inbuf->inputstate & INS_DLE_char) {
                                /* quoted DLE: clear quote flag */
                                inbuf->inputstate &= ~INS_DLE_char;
                        } else if (cs->dle ||
                                   (inbuf->inputstate & INS_DLE_command)) {
                                /* DLE escape, pass up for handling */
                                inbuf->inputstate |= INS_DLE_char;
                                goto exit;
                        }
                        /* quoted or not in DLE mode: treat as regular data */
                        /* --v-- fall through --v-- */
                default:
                        /* append to line buffer if possible */
                        if (cbytes < MAX_RESP_SIZE)
                                cs->respdata[cbytes] = c;
                        cbytes++;
                }
        }
exit:
        cs->cbytes = cbytes;
        return procbytes;
}

/* process a block of received bytes in lock mode
 * All received bytes are passed unmodified to the tty i/f.
 * Return value:
 *      number of processed bytes
 */
static unsigned lock_loop(unsigned numbytes, struct inbuf_t *inbuf)
{
        unsigned char *src = inbuf->data + inbuf->head;

        gigaset_dbg_buffer(DEBUG_LOCKCMD, "received response", numbytes, src);
        gigaset_if_receive(inbuf->cs, src, numbytes);
        return numbytes;
}

/* process a block of received bytes in HDLC data mode
 * (mstate != MS_LOCKED && !(inputstate & INS_command) && proto2 == L2_HDLC)
 * Collect HDLC frames, undoing byte stuffing and watching for DLE escapes.
 * When a frame is complete, check the FCS and pass valid frames to the LL.
 * If DLE is encountered, return immediately to let the caller handle it.
 * Return value:
 *      number of processed bytes
 */
static unsigned hdlc_loop(unsigned numbytes, struct inbuf_t *inbuf)
{
        struct cardstate *cs = inbuf->cs;
        struct bc_state *bcs = cs->bcs;
        int inputstate = bcs->inputstate;
        __u16 fcs = bcs->rx_fcs;
        struct sk_buff *skb = bcs->rx_skb;
        unsigned char *src = inbuf->data + inbuf->head;
        unsigned procbytes = 0;
        unsigned char c;

        if (inputstate & INS_byte_stuff) {
                if (!numbytes)
                        return 0;
                inputstate &= ~INS_byte_stuff;
                goto byte_stuff;
        }

        while (procbytes < numbytes) {
                c = *src++;
                procbytes++;
                if (c == DLE_FLAG) {
                        if (inputstate & INS_DLE_char) {
                                /* quoted DLE: clear quote flag */
                                inputstate &= ~INS_DLE_char;
                        } else if (cs->dle || (inputstate & INS_DLE_command)) {
                                /* DLE escape, pass up for handling */
                                inputstate |= INS_DLE_char;
                                break;
                        }
                }

                if (c == PPP_ESCAPE) {
                        /* byte stuffing indicator: pull in next byte */
                        if (procbytes >= numbytes) {
                                /* end of buffer, save for later processing */
                                inputstate |= INS_byte_stuff;
                                break;
                        }
byte_stuff:
                        c = *src++;
                        procbytes++;
                        if (c == DLE_FLAG) {
                                if (inputstate & INS_DLE_char) {
                                        /* quoted DLE: clear quote flag */
                                        inputstate &= ~INS_DLE_char;
                                } else if (cs->dle ||
                                           (inputstate & INS_DLE_command)) {
                                        /* DLE escape, pass up for handling */
                                        inputstate |=
                                                INS_DLE_char | INS_byte_stuff;
                                        break;
                                }
                        }
                        c ^= PPP_TRANS;
#ifdef CONFIG_GIGASET_DEBUG
                        if (!muststuff(c))
                                gig_dbg(DEBUG_HDLC, "byte stuffed: 0x%02x", c);
#endif
                } else if (c == PPP_FLAG) {
                        /* end of frame: process content if any */
                        if (inputstate & INS_have_data) {
                                gig_dbg(DEBUG_HDLC,
                                        "7e----------------------------");

                                /* check and pass received frame */
                                if (!skb) {
                                        /* skipped frame */
                                        gigaset_isdn_rcv_err(bcs);
                                } else if (skb->len < 2) {
                                        /* frame too short for FCS */
                                        dev_warn(cs->dev,
                                                 "short frame (%d)\n",
                                                 skb->len);
                                        gigaset_isdn_rcv_err(bcs);
                                        dev_kfree_skb_any(skb);
                                } else if (fcs != PPP_GOODFCS) {
                                        /* frame check error */
                                        dev_err(cs->dev,
                                                "Checksum failed, %u bytes corrupted!\n",
                                                skb->len);
                                        gigaset_isdn_rcv_err(bcs);
                                        dev_kfree_skb_any(skb);
                                } else {
                                        /* good frame */
                                        __skb_trim(skb, skb->len - 2);
                                        gigaset_skb_rcvd(bcs, skb);
                                }

                                /* prepare reception of next frame */
                                inputstate &= ~INS_have_data;
                                skb = gigaset_new_rx_skb(bcs);
                        } else {
                                /* empty frame (7E 7E) */
#ifdef CONFIG_GIGASET_DEBUG
                                ++bcs->emptycount;
#endif
                                if (!skb) {
                                        /* skipped (?) */
                                        gigaset_isdn_rcv_err(bcs);
                                        skb = gigaset_new_rx_skb(bcs);
                                }
                        }

                        fcs = PPP_INITFCS;
                        continue;
#ifdef CONFIG_GIGASET_DEBUG
                } else if (muststuff(c)) {
                        /* Should not happen. Possible after ZDLE=1<CR><LF>. */
                        gig_dbg(DEBUG_HDLC, "not byte stuffed: 0x%02x", c);
#endif
                }

                /* regular data byte, append to skb */
#ifdef CONFIG_GIGASET_DEBUG
                if (!(inputstate & INS_have_data)) {
                        gig_dbg(DEBUG_HDLC, "7e (%d x) ================",
                                bcs->emptycount);
                        bcs->emptycount = 0;
                }
#endif
                inputstate |= INS_have_data;
                if (skb) {
                        if (skb->len >= bcs->rx_bufsize) {
                                dev_warn(cs->dev, "received packet too long\n");
                                dev_kfree_skb_any(skb);
                                /* skip remainder of packet */
                                bcs->rx_skb = skb = NULL;
                        } else {
                                *__skb_put(skb, 1) = c;
                                fcs = crc_ccitt_byte(fcs, c);
                        }
                }
        }

        bcs->inputstate = inputstate;
        bcs->rx_fcs = fcs;
        return procbytes;
}

/* process a block of received bytes in transparent data mode
 * (mstate != MS_LOCKED && !(inputstate & INS_command) && proto2 != L2_HDLC)
 * Invert bytes, undoing byte stuffing and watching for DLE escapes.
 * If DLE is encountered, return immediately to let the caller handle it.
 * Return value:
 *      number of processed bytes
 */
static unsigned iraw_loop(unsigned numbytes, struct inbuf_t *inbuf)
{
        struct cardstate *cs = inbuf->cs;
        struct bc_state *bcs = cs->bcs;
        int inputstate = bcs->inputstate;
        struct sk_buff *skb = bcs->rx_skb;
        unsigned char *src = inbuf->data + inbuf->head;
        unsigned procbytes = 0;
        unsigned char c;

        if (!skb) {
                /* skip this block */
                gigaset_new_rx_skb(bcs);
                return numbytes;
        }

        while (procbytes < numbytes && skb->len < bcs->rx_bufsize) {
                c = *src++;
                procbytes++;

                if (c == DLE_FLAG) {
                        if (inputstate & INS_DLE_char) {
                                /* quoted DLE: clear quote flag */
                                inputstate &= ~INS_DLE_char;
                        } else if (cs->dle || (inputstate & INS_DLE_command)) {
                                /* DLE escape, pass up for handling */
                                inputstate |= INS_DLE_char;
                                break;
                        }
                }

                /* regular data byte: append to current skb */
                inputstate |= INS_have_data;
                *__skb_put(skb, 1) = bitrev8(c);
        }

        /* pass data up */
        if (inputstate & INS_have_data) {
                gigaset_skb_rcvd(bcs, skb);
                inputstate &= ~INS_have_data;
                gigaset_new_rx_skb(bcs);
        }

        bcs->inputstate = inputstate;
        return procbytes;
}

/* process DLE escapes
 * Called whenever a DLE sequence might be encountered in the input stream.
 * Either processes the entire DLE sequence or, if that isn't possible,
 * notes the fact that an initial DLE has been received in the INS_DLE_char
 * inputstate flag and resumes processing of the sequence on the next call.
 */
static void handle_dle(struct inbuf_t *inbuf)
{
        struct cardstate *cs = inbuf->cs;

        if (cs->mstate == MS_LOCKED)
                return;         /* no DLE processing in lock mode */

        if (!(inbuf->inputstate & INS_DLE_char)) {
                /* no DLE pending */
                if (inbuf->data[inbuf->head] == DLE_FLAG &&
                    (cs->dle || inbuf->inputstate & INS_DLE_command)) {
                        /* start of DLE sequence */
                        inbuf->head++;
                        if (inbuf->head == inbuf->tail ||
                            inbuf->head == RBUFSIZE) {
                                /* end of buffer, save for later processing */
                                inbuf->inputstate |= INS_DLE_char;
                                return;
                        }
                } else {
                        /* regular data byte */
                        return;
                }
        }

        /* consume pending DLE */
        inbuf->inputstate &= ~INS_DLE_char;

        switch (inbuf->data[inbuf->head]) {
        case 'X':       /* begin of event message */
                if (inbuf->inputstate & INS_command)
                        dev_notice(cs->dev,
                                   "received <DLE>X in command mode\n");
                inbuf->inputstate |= INS_command | INS_DLE_command;
                inbuf->head++;  /* byte consumed */
                break;
        case '.':       /* end of event message */
                if (!(inbuf->inputstate & INS_DLE_command))
                        dev_notice(cs->dev,
                                   "received <DLE>. without <DLE>X\n");
                inbuf->inputstate &= ~INS_DLE_command;
                /* return to data mode if in DLE mode */
                if (cs->dle)
                        inbuf->inputstate &= ~INS_command;
                inbuf->head++;  /* byte consumed */
                break;
        case DLE_FLAG:  /* DLE in data stream */
                /* mark as quoted */
                inbuf->inputstate |= INS_DLE_char;
                if (!(cs->dle || inbuf->inputstate & INS_DLE_command))
                        dev_notice(cs->dev,
                                   "received <DLE><DLE> not in DLE mode\n");
                break;  /* quoted byte left in buffer */
        default:
                dev_notice(cs->dev, "received <DLE><%02x>\n",
                           inbuf->data[inbuf->head]);
                /* quoted byte left in buffer */
        }
}

/**
 * gigaset_m10x_input() - process a block of data received from the device
 * @inbuf:      received data and device descriptor structure.
 *
 * Called by hardware module {ser,usb}_gigaset with a block of received
 * bytes. Separates the bytes received over the serial data channel into
 * user data and command replies (locked/unlocked) according to the
 * current state of the interface.
 */
void gigaset_m10x_input(struct inbuf_t *inbuf)
{
        struct cardstate *cs = inbuf->cs;
        unsigned numbytes, procbytes;

        gig_dbg(DEBUG_INTR, "buffer state: %u -> %u", inbuf->head, inbuf->tail);

        while (inbuf->head != inbuf->tail) {
                /* check for DLE escape */
                handle_dle(inbuf);

                /* process a contiguous block of bytes */
                numbytes = (inbuf->head > inbuf->tail ?
                            RBUFSIZE : inbuf->tail) - inbuf->head;
                gig_dbg(DEBUG_INTR, "processing %u bytes", numbytes);
                /*
                 * numbytes may be 0 if handle_dle() ate the last byte.
                 * This does no harm, *_loop() will just return 0 immediately.
                 */

                if (cs->mstate == MS_LOCKED)
                        procbytes = lock_loop(numbytes, inbuf);
                else if (inbuf->inputstate & INS_command)
                        procbytes = cmd_loop(numbytes, inbuf);
                else if (cs->bcs->proto2 == L2_HDLC)
                        procbytes = hdlc_loop(numbytes, inbuf);
                else
                        procbytes = iraw_loop(numbytes, inbuf);
                inbuf->head += procbytes;

                /* check for buffer wraparound */
                if (inbuf->head >= RBUFSIZE)
                        inbuf->head = 0;

                gig_dbg(DEBUG_INTR, "head set to %u", inbuf->head);
        }
}
EXPORT_SYMBOL_GPL(gigaset_m10x_input);


/* == data output ========================================================== */

/*
 * Encode a data packet into an octet stuffed HDLC frame with FCS,
 * opening and closing flags, preserving headroom data.
 * parameters:
 *      skb             skb containing original packet (freed upon return)
 * Return value:
 *      pointer to newly allocated skb containing the result frame
 *      and the original link layer header, NULL on error
 */
static struct sk_buff *HDLC_Encode(struct sk_buff *skb)
{
        struct sk_buff *hdlc_skb;
        __u16 fcs;
        unsigned char c;
        unsigned char *cp;
        int len;
        unsigned int stuf_cnt;

        stuf_cnt = 0;
        fcs = PPP_INITFCS;
        cp = skb->data;
        len = skb->len;
        while (len--) {
                if (muststuff(*cp))
                        stuf_cnt++;
                fcs = crc_ccitt_byte(fcs, *cp++);
        }
        fcs ^= 0xffff;                  /* complement */

        /* size of new buffer: original size + number of stuffing bytes
         * + 2 bytes FCS + 2 stuffing bytes for FCS (if needed) + 2 flag bytes
         * + room for link layer header
         */
        hdlc_skb = dev_alloc_skb(skb->len + stuf_cnt + 6 + skb->mac_len);
        if (!hdlc_skb) {
                dev_kfree_skb_any(skb);
                return NULL;
        }

        /* Copy link layer header into new skb */
        skb_reset_mac_header(hdlc_skb);
        skb_reserve(hdlc_skb, skb->mac_len);
        memcpy(skb_mac_header(hdlc_skb), skb_mac_header(skb), skb->mac_len);
        hdlc_skb->mac_len = skb->mac_len;

        /* Add flag sequence in front of everything.. */
        *(skb_put(hdlc_skb, 1)) = PPP_FLAG;

        /* Perform byte stuffing while copying data. */
        while (skb->len--) {
                if (muststuff(*skb->data)) {
                        *(skb_put(hdlc_skb, 1)) = PPP_ESCAPE;
                        *(skb_put(hdlc_skb, 1)) = (*skb->data++) ^ PPP_TRANS;
                } else
                        *(skb_put(hdlc_skb, 1)) = *skb->data++;
        }

        /* Finally add FCS (byte stuffed) and flag sequence */
        c = (fcs & 0x00ff);     /* least significant byte first */
        if (muststuff(c)) {
                *(skb_put(hdlc_skb, 1)) = PPP_ESCAPE;
                c ^= PPP_TRANS;
        }
        *(skb_put(hdlc_skb, 1)) = c;

        c = ((fcs >> 8) & 0x00ff);
        if (muststuff(c)) {
                *(skb_put(hdlc_skb, 1)) = PPP_ESCAPE;
                c ^= PPP_TRANS;
        }
        *(skb_put(hdlc_skb, 1)) = c;

        *(skb_put(hdlc_skb, 1)) = PPP_FLAG;

        dev_kfree_skb_any(skb);
        return hdlc_skb;
}

/*
 * Encode a data packet into an octet stuffed raw bit inverted frame,
 * preserving headroom data.
 * parameters:
 *      skb             skb containing original packet (freed upon return)
 * Return value:
 *      pointer to newly allocated skb containing the result frame
 *      and the original link layer header, NULL on error
 */
static struct sk_buff *iraw_encode(struct sk_buff *skb)
{
        struct sk_buff *iraw_skb;
        unsigned char c;
        unsigned char *cp;
        int len;

        /* size of new buffer (worst case = every byte must be stuffed):
         * 2 * original size + room for link layer header
         */
        iraw_skb = dev_alloc_skb(2 * skb->len + skb->mac_len);
        if (!iraw_skb) {
                dev_kfree_skb_any(skb);
                return NULL;
        }

        /* copy link layer header into new skb */
        skb_reset_mac_header(iraw_skb);
        skb_reserve(iraw_skb, skb->mac_len);
        memcpy(skb_mac_header(iraw_skb), skb_mac_header(skb), skb->mac_len);
        iraw_skb->mac_len = skb->mac_len;

        /* copy and stuff data */
        cp = skb->data;
        len = skb->len;
        while (len--) {
                c = bitrev8(*cp++);
                if (c == DLE_FLAG)
                        *(skb_put(iraw_skb, 1)) = c;
                *(skb_put(iraw_skb, 1)) = c;
        }
        dev_kfree_skb_any(skb);
        return iraw_skb;
}

/**
 * gigaset_m10x_send_skb() - queue an skb for sending
 * @bcs:        B channel descriptor structure.
 * @skb:        data to send.
 *
 * Called by LL to encode and queue an skb for sending, and start
 * transmission if necessary.
 * Once the payload data has been transmitted completely, gigaset_skb_sent()
 * will be called with the skb's link layer header preserved.
 *
 * Return value:
 *      number of bytes accepted for sending (skb->len) if ok,
 *      error code < 0 (eg. -ENOMEM) on error
 */
int gigaset_m10x_send_skb(struct bc_state *bcs, struct sk_buff *skb)
{
        struct cardstate *cs = bcs->cs;
        unsigned len = skb->len;
        unsigned long flags;

        if (bcs->proto2 == L2_HDLC)
                skb = HDLC_Encode(skb);
        else
                skb = iraw_encode(skb);
        if (!skb) {
                dev_err(cs->dev,
                        "unable to allocate memory for encoding!\n");
                return -ENOMEM;
        }

        skb_queue_tail(&bcs->squeue, skb);
        spin_lock_irqsave(&cs->lock, flags);
        if (cs->connected)
                tasklet_schedule(&cs->write_tasklet);
        spin_unlock_irqrestore(&cs->lock, flags);

        return len;     /* ok so far */
}
EXPORT_SYMBOL_GPL(gigaset_m10x_send_skb);