// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Common data handling layer for bas_gigaset
 *
 * Copyright (c) 2005 by Tilman Schmidt <tilman@imap.cc>,
 *                       Hansjoerg Lipp <hjlipp@web.de>.
 *
 * =====================================================================
 * =====================================================================
 */

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

/* access methods for isowbuf_t */
/* ============================ */

/* initialize buffer structure
 */
void gigaset_isowbuf_init(struct isowbuf_t *iwb, unsigned char idle)
{
        iwb->read = 0;
        iwb->nextread = 0;
        iwb->write = 0;
        atomic_set(&iwb->writesem, 1);
        iwb->wbits = 0;
        iwb->idle = idle;
        memset(iwb->data + BAS_OUTBUFSIZE, idle, BAS_OUTBUFPAD);
}

/* compute number of bytes which can be appended to buffer
 * so that there is still room to append a maximum frame of flags
 */
static inline int isowbuf_freebytes(struct isowbuf_t *iwb)
{
        int read, write, freebytes;

        read = iwb->read;
        write = iwb->write;
        freebytes = read - write;
        if (freebytes > 0) {
                /* no wraparound: need padding space within regular area */
                return freebytes - BAS_OUTBUFPAD;
        } else if (read < BAS_OUTBUFPAD) {
                /* wraparound: can use space up to end of regular area */
                return BAS_OUTBUFSIZE - write;
        } else {
                /* following the wraparound yields more space */
                return freebytes + BAS_OUTBUFSIZE - BAS_OUTBUFPAD;
        }
}

/* start writing
 * acquire the write semaphore
 * return 0 if acquired, <0 if busy
 */
static inline int isowbuf_startwrite(struct isowbuf_t *iwb)
{
        if (!atomic_dec_and_test(&iwb->writesem)) {
                atomic_inc(&iwb->writesem);
                gig_dbg(DEBUG_ISO, "%s: couldn't acquire iso write semaphore",
                        __func__);
                return -EBUSY;
        }
        gig_dbg(DEBUG_ISO,
                "%s: acquired iso write semaphore, data[write]=%02x, nbits=%d",
                __func__, iwb->data[iwb->write], iwb->wbits);
        return 0;
}

/* finish writing
 * release the write semaphore
 * returns the current write position
 */
static inline int isowbuf_donewrite(struct isowbuf_t *iwb)
{
        int write = iwb->write;
        atomic_inc(&iwb->writesem);
        return write;
}

/* append bits to buffer without any checks
 * - data contains bits to append, starting at LSB
 * - nbits is number of bits to append (0..24)
 * must be called with the write semaphore held
 * If more than nbits bits are set in data, the extraneous bits are set in the
 * buffer too, but the write position is only advanced by nbits.
 */
static inline void isowbuf_putbits(struct isowbuf_t *iwb, u32 data, int nbits)
{
        int write = iwb->write;
        data <<= iwb->wbits;
        data |= iwb->data[write];
        nbits += iwb->wbits;
        while (nbits >= 8) {
                iwb->data[write++] = data & 0xff;
                write %= BAS_OUTBUFSIZE;
                data >>= 8;
                nbits -= 8;
        }
        iwb->wbits = nbits;
        iwb->data[write] = data & 0xff;
        iwb->write = write;
}

/* put final flag on HDLC bitstream
 * also sets the idle fill byte to the correspondingly shifted flag pattern
 * must be called with the write semaphore held
 */
static inline void isowbuf_putflag(struct isowbuf_t *iwb)
{
        int write;

        /* add two flags, thus reliably covering one byte */
        isowbuf_putbits(iwb, 0x7e7e, 8);
        /* recover the idle flag byte */
        write = iwb->write;
        iwb->idle = iwb->data[write];
        gig_dbg(DEBUG_ISO, "idle fill byte %02x", iwb->idle);
        /* mask extraneous bits in buffer */
        iwb->data[write] &= (1 << iwb->wbits) - 1;
}

/* retrieve a block of bytes for sending
 * The requested number of bytes is provided as a contiguous block.
 * If necessary, the frame is filled to the requested number of bytes
 * with the idle value.
 * returns offset to frame, < 0 on busy or error
 */
int gigaset_isowbuf_getbytes(struct isowbuf_t *iwb, int size)
{
        int read, write, limit, src, dst;
        unsigned char pbyte;

        read = iwb->nextread;
        write = iwb->write;
        if (likely(read == write)) {
                /* return idle frame */
                return read < BAS_OUTBUFPAD ?
                        BAS_OUTBUFSIZE : read - BAS_OUTBUFPAD;
        }

        limit = read + size;
        gig_dbg(DEBUG_STREAM, "%s: read=%d write=%d limit=%d",
                __func__, read, write, limit);
#ifdef CONFIG_GIGASET_DEBUG
        if (unlikely(size < 0 || size > BAS_OUTBUFPAD)) {
                pr_err("invalid size %d\n", size);
                return -EINVAL;
        }
#endif

        if (read < write) {
                /* no wraparound in valid data */
                if (limit >= write) {
                        /* append idle frame */
                        if (isowbuf_startwrite(iwb) < 0)
                                return -EBUSY;
                        /* write position could have changed */
                        write = iwb->write;
                        if (limit >= write) {
                                pbyte = iwb->data[write]; /* save
                                                             partial byte */
                                limit = write + BAS_OUTBUFPAD;
                                gig_dbg(DEBUG_STREAM,
                                        "%s: filling %d->%d with %02x",
                                        __func__, write, limit, iwb->idle);
                                if (write + BAS_OUTBUFPAD < BAS_OUTBUFSIZE)
                                        memset(iwb->data + write, iwb->idle,
                                               BAS_OUTBUFPAD);
                                else {
                                        /* wraparound, fill entire pad area */
                                        memset(iwb->data + write, iwb->idle,
                                               BAS_OUTBUFSIZE + BAS_OUTBUFPAD
                                               - write);
                                        limit = 0;
                                }
                                gig_dbg(DEBUG_STREAM,
                                        "%s: restoring %02x at %d",
                                        __func__, pbyte, limit);
                                iwb->data[limit] = pbyte; /* restore
                                                             partial byte */
                                iwb->write = limit;
                        }
                        isowbuf_donewrite(iwb);
                }
        } else {
                /* valid data wraparound */
                if (limit >= BAS_OUTBUFSIZE) {
                        /* copy wrapped part into pad area */
                        src = 0;
                        dst = BAS_OUTBUFSIZE;
                        while (dst < limit && src < write)
                                iwb->data[dst++] = iwb->data[src++];
                        if (dst <= limit) {
                                /* fill pad area with idle byte */
                                memset(iwb->data + dst, iwb->idle,
                                       BAS_OUTBUFSIZE + BAS_OUTBUFPAD - dst);
                        }
                        limit = src;
                }
        }
        iwb->nextread = limit;
        return read;
}

/* dump_bytes
 * write hex bytes to syslog for debugging
 */
static inline void dump_bytes(enum debuglevel level, const char *tag,
                              unsigned char *bytes, int count)
{
#ifdef CONFIG_GIGASET_DEBUG
        unsigned char c;
        static char dbgline[3 * 32 + 1];
        int i = 0;

        if (!(gigaset_debuglevel & level))
                return;

        while (count-- > 0) {
                if (i > sizeof(dbgline) - 4) {
                        dbgline[i] = '\0';
                        gig_dbg(level, "%s:%s", tag, dbgline);
                        i = 0;
                }
                c = *bytes++;
                dbgline[i] = (i && !(i % 12)) ? '-' : ' ';
                i++;
                dbgline[i++] = hex_asc_hi(c);
                dbgline[i++] = hex_asc_lo(c);
        }
        dbgline[i] = '\0';
        gig_dbg(level, "%s:%s", tag, dbgline);
#endif
}

/*============================================================================*/

/* bytewise HDLC bitstuffing via table lookup
 * lookup table: 5 subtables for 0..4 preceding consecutive '1' bits
 * index: 256*(number of preceding '1' bits) + (next byte to stuff)
 * value: bit  9.. 0 = result bits
 *        bit 12..10 = number of trailing '1' bits in result
 *        bit 14..13 = number of bits added by stuffing
 */
static const u16 stufftab[5 * 256] = {
/* previous 1s = 0: */
        0x0000, 0x0001, 0x0002, 0x0003, 0x0004, 0x0005, 0x0006, 0x0007, 0x0008, 0x0009, 0x000a, 0x000b, 0x000c, 0x000d, 0x000e, 0x000f,
        0x0010, 0x0011, 0x0012, 0x0013, 0x0014, 0x0015, 0x0016, 0x0017, 0x0018, 0x0019, 0x001a, 0x001b, 0x001c, 0x001d, 0x001e, 0x201f,
        0x0020, 0x0021, 0x0022, 0x0023, 0x0024, 0x0025, 0x0026, 0x0027, 0x0028, 0x0029, 0x002a, 0x002b, 0x002c, 0x002d, 0x002e, 0x002f,
        0x0030, 0x0031, 0x0032, 0x0033, 0x0034, 0x0035, 0x0036, 0x0037, 0x0038, 0x0039, 0x003a, 0x003b, 0x003c, 0x003d, 0x203e, 0x205f,
        0x0040, 0x0041, 0x0042, 0x0043, 0x0044, 0x0045, 0x0046, 0x0047, 0x0048, 0x0049, 0x004a, 0x004b, 0x004c, 0x004d, 0x004e, 0x004f,
        0x0050, 0x0051, 0x0052, 0x0053, 0x0054, 0x0055, 0x0056, 0x0057, 0x0058, 0x0059, 0x005a, 0x005b, 0x005c, 0x005d, 0x005e, 0x209f,
        0x0060, 0x0061, 0x0062, 0x0063, 0x0064, 0x0065, 0x0066, 0x0067, 0x0068, 0x0069, 0x006a, 0x006b, 0x006c, 0x006d, 0x006e, 0x006f,
        0x0070, 0x0071, 0x0072, 0x0073, 0x0074, 0x0075, 0x0076, 0x0077, 0x0078, 0x0079, 0x007a, 0x007b, 0x207c, 0x207d, 0x20be, 0x20df,
        0x0480, 0x0481, 0x0482, 0x0483, 0x0484, 0x0485, 0x0486, 0x0487, 0x0488, 0x0489, 0x048a, 0x048b, 0x048c, 0x048d, 0x048e, 0x048f,
        0x0490, 0x0491, 0x0492, 0x0493, 0x0494, 0x0495, 0x0496, 0x0497, 0x0498, 0x0499, 0x049a, 0x049b, 0x049c, 0x049d, 0x049e, 0x251f,
        0x04a0, 0x04a1, 0x04a2, 0x04a3, 0x04a4, 0x04a5, 0x04a6, 0x04a7, 0x04a8, 0x04a9, 0x04aa, 0x04ab, 0x04ac, 0x04ad, 0x04ae, 0x04af,
        0x04b0, 0x04b1, 0x04b2, 0x04b3, 0x04b4, 0x04b5, 0x04b6, 0x04b7, 0x04b8, 0x04b9, 0x04ba, 0x04bb, 0x04bc, 0x04bd, 0x253e, 0x255f,
        0x08c0, 0x08c1, 0x08c2, 0x08c3, 0x08c4, 0x08c5, 0x08c6, 0x08c7, 0x08c8, 0x08c9, 0x08ca, 0x08cb, 0x08cc, 0x08cd, 0x08ce, 0x08cf,
        0x08d0, 0x08d1, 0x08d2, 0x08d3, 0x08d4, 0x08d5, 0x08d6, 0x08d7, 0x08d8, 0x08d9, 0x08da, 0x08db, 0x08dc, 0x08dd, 0x08de, 0x299f,
        0x0ce0, 0x0ce1, 0x0ce2, 0x0ce3, 0x0ce4, 0x0ce5, 0x0ce6, 0x0ce7, 0x0ce8, 0x0ce9, 0x0cea, 0x0ceb, 0x0cec, 0x0ced, 0x0cee, 0x0cef,
        0x10f0, 0x10f1, 0x10f2, 0x10f3, 0x10f4, 0x10f5, 0x10f6, 0x10f7, 0x20f8, 0x20f9, 0x20fa, 0x20fb, 0x257c, 0x257d, 0x29be, 0x2ddf,

/* previous 1s = 1: */
        0x0000, 0x0001, 0x0002, 0x0003, 0x0004, 0x0005, 0x0006, 0x0007, 0x0008, 0x0009, 0x000a, 0x000b, 0x000c, 0x000d, 0x000e, 0x200f,
        0x0010, 0x0011, 0x0012, 0x0013, 0x0014, 0x0015, 0x0016, 0x0017, 0x0018, 0x0019, 0x001a, 0x001b, 0x001c, 0x001d, 0x001e, 0x202f,
        0x0020, 0x0021, 0x0022, 0x0023, 0x0024, 0x0025, 0x0026, 0x0027, 0x0028, 0x0029, 0x002a, 0x002b, 0x002c, 0x002d, 0x002e, 0x204f,
        0x0030, 0x0031, 0x0032, 0x0033, 0x0034, 0x0035, 0x0036, 0x0037, 0x0038, 0x0039, 0x003a, 0x003b, 0x003c, 0x003d, 0x203e, 0x206f,
        0x0040, 0x0041, 0x0042, 0x0043, 0x0044, 0x0045, 0x0046, 0x0047, 0x0048, 0x0049, 0x004a, 0x004b, 0x004c, 0x004d, 0x004e, 0x208f,
        0x0050, 0x0051, 0x0052, 0x0053, 0x0054, 0x0055, 0x0056, 0x0057, 0x0058, 0x0059, 0x005a, 0x005b, 0x005c, 0x005d, 0x005e, 0x20af,
        0x0060, 0x0061, 0x0062, 0x0063, 0x0064, 0x0065, 0x0066, 0x0067, 0x0068, 0x0069, 0x006a, 0x006b, 0x006c, 0x006d, 0x006e, 0x20cf,
        0x0070, 0x0071, 0x0072, 0x0073, 0x0074, 0x0075, 0x0076, 0x0077, 0x0078, 0x0079, 0x007a, 0x007b, 0x207c, 0x207d, 0x20be, 0x20ef,
        0x0480, 0x0481, 0x0482, 0x0483, 0x0484, 0x0485, 0x0486, 0x0487, 0x0488, 0x0489, 0x048a, 0x048b, 0x048c, 0x048d, 0x048e, 0x250f,
        0x0490, 0x0491, 0x0492, 0x0493, 0x0494, 0x0495, 0x0496, 0x0497, 0x0498, 0x0499, 0x049a, 0x049b, 0x049c, 0x049d, 0x049e, 0x252f,
        0x04a0, 0x04a1, 0x04a2, 0x04a3, 0x04a4, 0x04a5, 0x04a6, 0x04a7, 0x04a8, 0x04a9, 0x04aa, 0x04ab, 0x04ac, 0x04ad, 0x04ae, 0x254f,
        0x04b0, 0x04b1, 0x04b2, 0x04b3, 0x04b4, 0x04b5, 0x04b6, 0x04b7, 0x04b8, 0x04b9, 0x04ba, 0x04bb, 0x04bc, 0x04bd, 0x253e, 0x256f,
        0x08c0, 0x08c1, 0x08c2, 0x08c3, 0x08c4, 0x08c5, 0x08c6, 0x08c7, 0x08c8, 0x08c9, 0x08ca, 0x08cb, 0x08cc, 0x08cd, 0x08ce, 0x298f,
        0x08d0, 0x08d1, 0x08d2, 0x08d3, 0x08d4, 0x08d5, 0x08d6, 0x08d7, 0x08d8, 0x08d9, 0x08da, 0x08db, 0x08dc, 0x08dd, 0x08de, 0x29af,
        0x0ce0, 0x0ce1, 0x0ce2, 0x0ce3, 0x0ce4, 0x0ce5, 0x0ce6, 0x0ce7, 0x0ce8, 0x0ce9, 0x0cea, 0x0ceb, 0x0cec, 0x0ced, 0x0cee, 0x2dcf,
        0x10f0, 0x10f1, 0x10f2, 0x10f3, 0x10f4, 0x10f5, 0x10f6, 0x10f7, 0x20f8, 0x20f9, 0x20fa, 0x20fb, 0x257c, 0x257d, 0x29be, 0x31ef,

/* previous 1s = 2: */
        0x0000, 0x0001, 0x0002, 0x0003, 0x0004, 0x0005, 0x0006, 0x2007, 0x0008, 0x0009, 0x000a, 0x000b, 0x000c, 0x000d, 0x000e, 0x2017,
        0x0010, 0x0011, 0x0012, 0x0013, 0x0014, 0x0015, 0x0016, 0x2027, 0x0018, 0x0019, 0x001a, 0x001b, 0x001c, 0x001d, 0x001e, 0x2037,
        0x0020, 0x0021, 0x0022, 0x0023, 0x0024, 0x0025, 0x0026, 0x2047, 0x0028, 0x0029, 0x002a, 0x002b, 0x002c, 0x002d, 0x002e, 0x2057,
        0x0030, 0x0031, 0x0032, 0x0033, 0x0034, 0x0035, 0x0036, 0x2067, 0x0038, 0x0039, 0x003a, 0x003b, 0x003c, 0x003d, 0x203e, 0x2077,
        0x0040, 0x0041, 0x0042, 0x0043, 0x0044, 0x0045, 0x0046, 0x2087, 0x0048, 0x0049, 0x004a, 0x004b, 0x004c, 0x004d, 0x004e, 0x2097,
        0x0050, 0x0051, 0x0052, 0x0053, 0x0054, 0x0055, 0x0056, 0x20a7, 0x0058, 0x0059, 0x005a, 0x005b, 0x005c, 0x005d, 0x005e, 0x20b7,
        0x0060, 0x0061, 0x0062, 0x0063, 0x0064, 0x0065, 0x0066, 0x20c7, 0x0068, 0x0069, 0x006a, 0x006b, 0x006c, 0x006d, 0x006e, 0x20d7,
        0x0070, 0x0071, 0x0072, 0x0073, 0x0074, 0x0075, 0x0076, 0x20e7, 0x0078, 0x0079, 0x007a, 0x007b, 0x207c, 0x207d, 0x20be, 0x20f7,
        0x0480, 0x0481, 0x0482, 0x0483, 0x0484, 0x0485, 0x0486, 0x2507, 0x0488, 0x0489, 0x048a, 0x048b, 0x048c, 0x048d, 0x048e, 0x2517,
        0x0490, 0x0491, 0x0492, 0x0493, 0x0494, 0x0495, 0x0496, 0x2527, 0x0498, 0x0499, 0x049a, 0x049b, 0x049c, 0x049d, 0x049e, 0x2537,
        0x04a0, 0x04a1, 0x04a2, 0x04a3, 0x04a4, 0x04a5, 0x04a6, 0x2547, 0x04a8, 0x04a9, 0x04aa, 0x04ab, 0x04ac, 0x04ad, 0x04ae, 0x2557,
        0x04b0, 0x04b1, 0x04b2, 0x04b3, 0x04b4, 0x04b5, 0x04b6, 0x2567, 0x04b8, 0x04b9, 0x04ba, 0x04bb, 0x04bc, 0x04bd, 0x253e, 0x2577,
        0x08c0, 0x08c1, 0x08c2, 0x08c3, 0x08c4, 0x08c5, 0x08c6, 0x2987, 0x08c8, 0x08c9, 0x08ca, 0x08cb, 0x08cc, 0x08cd, 0x08ce, 0x2997,
        0x08d0, 0x08d1, 0x08d2, 0x08d3, 0x08d4, 0x08d5, 0x08d6, 0x29a7, 0x08d8, 0x08d9, 0x08da, 0x08db, 0x08dc, 0x08dd, 0x08de, 0x29b7,
        0x0ce0, 0x0ce1, 0x0ce2, 0x0ce3, 0x0ce4, 0x0ce5, 0x0ce6, 0x2dc7, 0x0ce8, 0x0ce9, 0x0cea, 0x0ceb, 0x0cec, 0x0ced, 0x0cee, 0x2dd7,
        0x10f0, 0x10f1, 0x10f2, 0x10f3, 0x10f4, 0x10f5, 0x10f6, 0x31e7, 0x20f8, 0x20f9, 0x20fa, 0x20fb, 0x257c, 0x257d, 0x29be, 0x41f7,

/* previous 1s = 3: */
        0x0000, 0x0001, 0x0002, 0x2003, 0x0004, 0x0005, 0x0006, 0x200b, 0x0008, 0x0009, 0x000a, 0x2013, 0x000c, 0x000d, 0x000e, 0x201b,
        0x0010, 0x0011, 0x0012, 0x2023, 0x0014, 0x0015, 0x0016, 0x202b, 0x0018, 0x0019, 0x001a, 0x2033, 0x001c, 0x001d, 0x001e, 0x203b,
        0x0020, 0x0021, 0x0022, 0x2043, 0x0024, 0x0025, 0x0026, 0x204b, 0x0028, 0x0029, 0x002a, 0x2053, 0x002c, 0x002d, 0x002e, 0x205b,
        0x0030, 0x0031, 0x0032, 0x2063, 0x0034, 0x0035, 0x0036, 0x206b, 0x0038, 0x0039, 0x003a, 0x2073, 0x003c, 0x003d, 0x203e, 0x207b,
        0x0040, 0x0041, 0x0042, 0x2083, 0x0044, 0x0045, 0x0046, 0x208b, 0x0048, 0x0049, 0x004a, 0x2093, 0x004c, 0x004d, 0x004e, 0x209b,
        0x0050, 0x0051, 0x0052, 0x20a3, 0x0054, 0x0055, 0x0056, 0x20ab, 0x0058, 0x0059, 0x005a, 0x20b3, 0x005c, 0x005d, 0x005e, 0x20bb,
        0x0060, 0x0061, 0x0062, 0x20c3, 0x0064, 0x0065, 0x0066, 0x20cb, 0x0068, 0x0069, 0x006a, 0x20d3, 0x006c, 0x006d, 0x006e, 0x20db,
        0x0070, 0x0071, 0x0072, 0x20e3, 0x0074, 0x0075, 0x0076, 0x20eb, 0x0078, 0x0079, 0x007a, 0x20f3, 0x207c, 0x207d, 0x20be, 0x40fb,
        0x0480, 0x0481, 0x0482, 0x2503, 0x0484, 0x0485, 0x0486, 0x250b, 0x0488, 0x0489, 0x048a, 0x2513, 0x048c, 0x048d, 0x048e, 0x251b,
        0x0490, 0x0491, 0x0492, 0x2523, 0x0494, 0x0495, 0x0496, 0x252b, 0x0498, 0x0499, 0x049a, 0x2533, 0x049c, 0x049d, 0x049e, 0x253b,
        0x04a0, 0x04a1, 0x04a2, 0x2543, 0x04a4, 0x04a5, 0x04a6, 0x254b, 0x04a8, 0x04a9, 0x04aa, 0x2553, 0x04ac, 0x04ad, 0x04ae, 0x255b,
        0x04b0, 0x04b1, 0x04b2, 0x2563, 0x04b4, 0x04b5, 0x04b6, 0x256b, 0x04b8, 0x04b9, 0x04ba, 0x2573, 0x04bc, 0x04bd, 0x253e, 0x257b,
        0x08c0, 0x08c1, 0x08c2, 0x2983, 0x08c4, 0x08c5, 0x08c6, 0x298b, 0x08c8, 0x08c9, 0x08ca, 0x2993, 0x08cc, 0x08cd, 0x08ce, 0x299b,
        0x08d0, 0x08d1, 0x08d2, 0x29a3, 0x08d4, 0x08d5, 0x08d6, 0x29ab, 0x08d8, 0x08d9, 0x08da, 0x29b3, 0x08dc, 0x08dd, 0x08de, 0x29bb,
        0x0ce0, 0x0ce1, 0x0ce2, 0x2dc3, 0x0ce4, 0x0ce5, 0x0ce6, 0x2dcb, 0x0ce8, 0x0ce9, 0x0cea, 0x2dd3, 0x0cec, 0x0ced, 0x0cee, 0x2ddb,
        0x10f0, 0x10f1, 0x10f2, 0x31e3, 0x10f4, 0x10f5, 0x10f6, 0x31eb, 0x20f8, 0x20f9, 0x20fa, 0x41f3, 0x257c, 0x257d, 0x29be, 0x46fb,

/* previous 1s = 4: */
        0x0000, 0x2001, 0x0002, 0x2005, 0x0004, 0x2009, 0x0006, 0x200d, 0x0008, 0x2011, 0x000a, 0x2015, 0x000c, 0x2019, 0x000e, 0x201d,
        0x0010, 0x2021, 0x0012, 0x2025, 0x0014, 0x2029, 0x0016, 0x202d, 0x0018, 0x2031, 0x001a, 0x2035, 0x001c, 0x2039, 0x001e, 0x203d,
        0x0020, 0x2041, 0x0022, 0x2045, 0x0024, 0x2049, 0x0026, 0x204d, 0x0028, 0x2051, 0x002a, 0x2055, 0x002c, 0x2059, 0x002e, 0x205d,
        0x0030, 0x2061, 0x0032, 0x2065, 0x0034, 0x2069, 0x0036, 0x206d, 0x0038, 0x2071, 0x003a, 0x2075, 0x003c, 0x2079, 0x203e, 0x407d,
        0x0040, 0x2081, 0x0042, 0x2085, 0x0044, 0x2089, 0x0046, 0x208d, 0x0048, 0x2091, 0x004a, 0x2095, 0x004c, 0x2099, 0x004e, 0x209d,
        0x0050, 0x20a1, 0x0052, 0x20a5, 0x0054, 0x20a9, 0x0056, 0x20ad, 0x0058, 0x20b1, 0x005a, 0x20b5, 0x005c, 0x20b9, 0x005e, 0x20bd,
        0x0060, 0x20c1, 0x0062, 0x20c5, 0x0064, 0x20c9, 0x0066, 0x20cd, 0x0068, 0x20d1, 0x006a, 0x20d5, 0x006c, 0x20d9, 0x006e, 0x20dd,
        0x0070, 0x20e1, 0x0072, 0x20e5, 0x0074, 0x20e9, 0x0076, 0x20ed, 0x0078, 0x20f1, 0x007a, 0x20f5, 0x207c, 0x40f9, 0x20be, 0x417d,
        0x0480, 0x2501, 0x0482, 0x2505, 0x0484, 0x2509, 0x0486, 0x250d, 0x0488, 0x2511, 0x048a, 0x2515, 0x048c, 0x2519, 0x048e, 0x251d,
        0x0490, 0x2521, 0x0492, 0x2525, 0x0494, 0x2529, 0x0496, 0x252d, 0x0498, 0x2531, 0x049a, 0x2535, 0x049c, 0x2539, 0x049e, 0x253d,
        0x04a0, 0x2541, 0x04a2, 0x2545, 0x04a4, 0x2549, 0x04a6, 0x254d, 0x04a8, 0x2551, 0x04aa, 0x2555, 0x04ac, 0x2559, 0x04ae, 0x255d,
        0x04b0, 0x2561, 0x04b2, 0x2565, 0x04b4, 0x2569, 0x04b6, 0x256d, 0x04b8, 0x2571, 0x04ba, 0x2575, 0x04bc, 0x2579, 0x253e, 0x467d,
        0x08c0, 0x2981, 0x08c2, 0x2985, 0x08c4, 0x2989, 0x08c6, 0x298d, 0x08c8, 0x2991, 0x08ca, 0x2995, 0x08cc, 0x2999, 0x08ce, 0x299d,
        0x08d0, 0x29a1, 0x08d2, 0x29a5, 0x08d4, 0x29a9, 0x08d6, 0x29ad, 0x08d8, 0x29b1, 0x08da, 0x29b5, 0x08dc, 0x29b9, 0x08de, 0x29bd,
        0x0ce0, 0x2dc1, 0x0ce2, 0x2dc5, 0x0ce4, 0x2dc9, 0x0ce6, 0x2dcd, 0x0ce8, 0x2dd1, 0x0cea, 0x2dd5, 0x0cec, 0x2dd9, 0x0cee, 0x2ddd,
        0x10f0, 0x31e1, 0x10f2, 0x31e5, 0x10f4, 0x31e9, 0x10f6, 0x31ed, 0x20f8, 0x41f1, 0x20fa, 0x41f5, 0x257c, 0x46f9, 0x29be, 0x4b7d
};

/* hdlc_bitstuff_byte
 * perform HDLC bitstuffing for one input byte (8 bits, LSB first)
 * parameters:
 *      cin     input byte
 *      ones    number of trailing '1' bits in result before this step
 *      iwb     pointer to output buffer structure
 *              (write semaphore must be held)
 * return value:
 *      number of trailing '1' bits in result after this step
 */

static inline int hdlc_bitstuff_byte(struct isowbuf_t *iwb, unsigned char cin,
                                     int ones)
{
        u16 stuff;
        int shiftinc, newones;

        /* get stuffing information for input byte
         * value: bit  9.. 0 = result bits
         *        bit 12..10 = number of trailing '1' bits in result
         *        bit 14..13 = number of bits added by stuffing
         */
        stuff = stufftab[256 * ones + cin];
        shiftinc = (stuff >> 13) & 3;
        newones = (stuff >> 10) & 7;
        stuff &= 0x3ff;

        /* append stuffed byte to output stream */
        isowbuf_putbits(iwb, stuff, 8 + shiftinc);
        return newones;
}

/* hdlc_buildframe
 * Perform HDLC framing with bitstuffing on a byte buffer
 * The input buffer is regarded as a sequence of bits, starting with the least
 * significant bit of the first byte and ending with the most significant bit
 * of the last byte. A 16 bit FCS is appended as defined by RFC 1662.
 * Whenever five consecutive '1' bits appear in the resulting bit sequence, a
 * '0' bit is inserted after them.
 * The resulting bit string and a closing flag pattern (PPP_FLAG, '01111110')
 * are appended to the output buffer starting at the given bit position, which
 * is assumed to already contain a leading flag.
 * The output buffer must have sufficient length; count + count/5 + 6 bytes
 * starting at *out are safe and are verified to be present.
 * parameters:
 *      in      input buffer
 *      count   number of bytes in input buffer
 *      iwb     pointer to output buffer structure
 *              (write semaphore must be held)
 * return value:
 *      position of end of packet in output buffer on success,
 *      -EAGAIN if write semaphore busy or buffer full
 */

static inline int hdlc_buildframe(struct isowbuf_t *iwb,
                                  unsigned char *in, int count)
{
        int ones;
        u16 fcs;
        int end;
        unsigned char c;

        if (isowbuf_freebytes(iwb) < count + count / 5 + 6 ||
            isowbuf_startwrite(iwb) < 0) {
                gig_dbg(DEBUG_ISO, "%s: %d bytes free -> -EAGAIN",
                        __func__, isowbuf_freebytes(iwb));
                return -EAGAIN;
        }

        dump_bytes(DEBUG_STREAM_DUMP, "snd data", in, count);

        /* bitstuff and checksum input data */
        fcs = PPP_INITFCS;
        ones = 0;
        while (count-- > 0) {
                c = *in++;
                ones = hdlc_bitstuff_byte(iwb, c, ones);
                fcs = crc_ccitt_byte(fcs, c);
        }

        /* bitstuff and append FCS
         * (complemented, least significant byte first) */
        fcs ^= 0xffff;
        ones = hdlc_bitstuff_byte(iwb, fcs & 0x00ff, ones);
        ones = hdlc_bitstuff_byte(iwb, (fcs >> 8) & 0x00ff, ones);

        /* put closing flag and repeat byte for flag idle */
        isowbuf_putflag(iwb);
        end = isowbuf_donewrite(iwb);
        return end;
}

/* trans_buildframe
 * Append a block of 'transparent' data to the output buffer,
 * inverting the bytes.
 * The output buffer must have sufficient length; count bytes
 * starting at *out are safe and are verified to be present.
 * parameters:
 *      in      input buffer
 *      count   number of bytes in input buffer
 *      iwb     pointer to output buffer structure
 *              (write semaphore must be held)
 * return value:
 *      position of end of packet in output buffer on success,
 *      -EAGAIN if write semaphore busy or buffer full
 */

static inline int trans_buildframe(struct isowbuf_t *iwb,
                                   unsigned char *in, int count)
{
        int write;
        unsigned char c;

        if (unlikely(count <= 0))
                return iwb->write;

        if (isowbuf_freebytes(iwb) < count ||
            isowbuf_startwrite(iwb) < 0) {
                gig_dbg(DEBUG_ISO, "can't put %d bytes", count);
                return -EAGAIN;
        }

        gig_dbg(DEBUG_STREAM, "put %d bytes", count);
        dump_bytes(DEBUG_STREAM_DUMP, "snd data", in, count);

        write = iwb->write;
        do {
                c = bitrev8(*in++);
                iwb->data[write++] = c;
                write %= BAS_OUTBUFSIZE;
        } while (--count > 0);
        iwb->write = write;
        iwb->idle = c;

        return isowbuf_donewrite(iwb);
}

int gigaset_isoc_buildframe(struct bc_state *bcs, unsigned char *in, int len)
{
        int result;

        switch (bcs->proto2) {
        case L2_HDLC:
                result = hdlc_buildframe(bcs->hw.bas->isooutbuf, in, len);
                gig_dbg(DEBUG_ISO, "%s: %d bytes HDLC -> %d",
                        __func__, len, result);
                break;
        default:                        /* assume transparent */
                result = trans_buildframe(bcs->hw.bas->isooutbuf, in, len);
                gig_dbg(DEBUG_ISO, "%s: %d bytes trans -> %d",
                        __func__, len, result);
        }
        return result;
}

/* hdlc_putbyte
 * append byte c to current skb of B channel structure *bcs, updating fcs
 */
static inline void hdlc_putbyte(unsigned char c, struct bc_state *bcs)
{
        bcs->rx_fcs = crc_ccitt_byte(bcs->rx_fcs, c);
        if (bcs->rx_skb == NULL)
                /* skipping */
                return;
        if (bcs->rx_skb->len >= bcs->rx_bufsize) {
                dev_warn(bcs->cs->dev, "received oversized packet discarded\n");
                bcs->hw.bas->giants++;
                dev_kfree_skb_any(bcs->rx_skb);
                bcs->rx_skb = NULL;
                return;
        }
        __skb_put_u8(bcs->rx_skb, c);
}

/* hdlc_flush
 * drop partial HDLC data packet
 */
static inline void hdlc_flush(struct bc_state *bcs)
{
        /* clear skb or allocate new if not skipping */
        if (bcs->rx_skb != NULL)
                skb_trim(bcs->rx_skb, 0);
        else
                gigaset_new_rx_skb(bcs);

        /* reset packet state */
        bcs->rx_fcs = PPP_INITFCS;
}

/* hdlc_done
 * process completed HDLC data packet
 */
static inline void hdlc_done(struct bc_state *bcs)
{
        struct cardstate *cs = bcs->cs;
        struct sk_buff *procskb;
        unsigned int len;

        if (unlikely(bcs->ignore)) {
                bcs->ignore--;
                hdlc_flush(bcs);
                return;
        }
        procskb = bcs->rx_skb;
        if (procskb == NULL) {
                /* previous error */
                gig_dbg(DEBUG_ISO, "%s: skb=NULL", __func__);
                gigaset_isdn_rcv_err(bcs);
        } else if (procskb->len < 2) {
                dev_notice(cs->dev, "received short frame (%d octets)\n",
                           procskb->len);
                bcs->hw.bas->runts++;
                dev_kfree_skb_any(procskb);
                gigaset_isdn_rcv_err(bcs);
        } else if (bcs->rx_fcs != PPP_GOODFCS) {
                dev_notice(cs->dev, "frame check error\n");
                bcs->hw.bas->fcserrs++;
                dev_kfree_skb_any(procskb);
                gigaset_isdn_rcv_err(bcs);
        } else {
                len = procskb->len;
                __skb_trim(procskb, len -= 2);  /* subtract FCS */
                gig_dbg(DEBUG_ISO, "%s: good frame (%d octets)", __func__, len);
                dump_bytes(DEBUG_STREAM_DUMP,
                           "rcv data", procskb->data, len);
                bcs->hw.bas->goodbytes += len;
                gigaset_skb_rcvd(bcs, procskb);
        }
        gigaset_new_rx_skb(bcs);
        bcs->rx_fcs = PPP_INITFCS;
}

/* hdlc_frag
 * drop HDLC data packet with non-integral last byte
 */
static inline void hdlc_frag(struct bc_state *bcs, unsigned inbits)
{
        if (unlikely(bcs->ignore)) {
                bcs->ignore--;
                hdlc_flush(bcs);
                return;
        }

        dev_notice(bcs->cs->dev, "received partial byte (%d bits)\n", inbits);
        bcs->hw.bas->alignerrs++;
        gigaset_isdn_rcv_err(bcs);
        __skb_trim(bcs->rx_skb, 0);
        bcs->rx_fcs = PPP_INITFCS;
}

/* bit counts lookup table for HDLC bit unstuffing
 * index: input byte
 * value: bit 0..3 = number of consecutive '1' bits starting from LSB
 *        bit 4..6 = number of consecutive '1' bits starting from MSB
 *                   (replacing 8 by 7 to make it fit; the algorithm won't care)
 *        bit 7 set if there are 5 or more "interior" consecutive '1' bits
 */
static const unsigned char bitcounts[256] = {
        0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00, 0x03, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00, 0x04,
        0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00, 0x03, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00, 0x05,
        0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00, 0x03, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00, 0x04,
        0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00, 0x03, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x80, 0x06,
        0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00, 0x03, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00, 0x04,
        0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00, 0x03, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00, 0x05,
        0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00, 0x03, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00, 0x04,
        0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00, 0x03, 0x00, 0x01, 0x00, 0x02, 0x80, 0x81, 0x80, 0x07,
        0x10, 0x11, 0x10, 0x12, 0x10, 0x11, 0x10, 0x13, 0x10, 0x11, 0x10, 0x12, 0x10, 0x11, 0x10, 0x14,
        0x10, 0x11, 0x10, 0x12, 0x10, 0x11, 0x10, 0x13, 0x10, 0x11, 0x10, 0x12, 0x10, 0x11, 0x10, 0x15,
        0x10, 0x11, 0x10, 0x12, 0x10, 0x11, 0x10, 0x13, 0x10, 0x11, 0x10, 0x12, 0x10, 0x11, 0x10, 0x14,
        0x10, 0x11, 0x10, 0x12, 0x10, 0x11, 0x10, 0x13, 0x10, 0x11, 0x10, 0x12, 0x10, 0x11, 0x90, 0x16,
        0x20, 0x21, 0x20, 0x22, 0x20, 0x21, 0x20, 0x23, 0x20, 0x21, 0x20, 0x22, 0x20, 0x21, 0x20, 0x24,
        0x20, 0x21, 0x20, 0x22, 0x20, 0x21, 0x20, 0x23, 0x20, 0x21, 0x20, 0x22, 0x20, 0x21, 0x20, 0x25,
        0x30, 0x31, 0x30, 0x32, 0x30, 0x31, 0x30, 0x33, 0x30, 0x31, 0x30, 0x32, 0x30, 0x31, 0x30, 0x34,
        0x40, 0x41, 0x40, 0x42, 0x40, 0x41, 0x40, 0x43, 0x50, 0x51, 0x50, 0x52, 0x60, 0x61, 0x70, 0x78
};

/* hdlc_unpack
 * perform HDLC frame processing (bit unstuffing, flag detection, FCS
 * calculation) on a sequence of received data bytes (8 bits each, LSB first)
 * pass on successfully received, complete frames as SKBs via gigaset_skb_rcvd
 * notify of errors via gigaset_isdn_rcv_err
 * tally frames, errors etc. in BC structure counters
 * parameters:
 *      src     received data
 *      count   number of received bytes
 *      bcs     receiving B channel structure
 */
static inline void hdlc_unpack(unsigned char *src, unsigned count,
                               struct bc_state *bcs)
{
        struct bas_bc_state *ubc = bcs->hw.bas;
        int inputstate;
        unsigned seqlen, inbyte, inbits;

        /* load previous state:
         * inputstate = set of flag bits:
         * - INS_flag_hunt: no complete opening flag received since connection
         *                  setup or last abort
         * - INS_have_data: at least one complete data byte received since last
         *                  flag
         * seqlen = number of consecutive '1' bits in last 7 input stream bits
         *          (0..7)
         * inbyte = accumulated partial data byte (if !INS_flag_hunt)
         * inbits = number of valid bits in inbyte, starting at LSB (0..6)
         */
        inputstate = bcs->inputstate;
        seqlen = ubc->seqlen;
        inbyte = ubc->inbyte;
        inbits = ubc->inbits;

        /* bit unstuffing a byte a time
         * Take your time to understand this; it's straightforward but tedious.
         * The "bitcounts" lookup table is used to speed up the counting of
         * leading and trailing '1' bits.
         */
        while (count--) {
                unsigned char c = *src++;
                unsigned char tabentry = bitcounts[c];
                unsigned lead1 = tabentry & 0x0f;
                unsigned trail1 = (tabentry >> 4) & 0x0f;

                seqlen += lead1;

                if (unlikely(inputstate & INS_flag_hunt)) {
                        if (c == PPP_FLAG) {
                                /* flag-in-one */
                                inputstate &= ~(INS_flag_hunt | INS_have_data);
                                inbyte = 0;
                                inbits = 0;
                        } else if (seqlen == 6 && trail1 != 7) {
                                /* flag completed & not followed by abort */
                                inputstate &= ~(INS_flag_hunt | INS_have_data);
                                inbyte = c >> (lead1 + 1);
                                inbits = 7 - lead1;
                                if (trail1 >= 8) {
                                        /* interior stuffing:
                                         * omitting the MSB handles most cases,
                                         * correct the incorrectly handled
                                         * cases individually */
                                        inbits--;
                                        switch (c) {
                                        case 0xbe:
                                                inbyte = 0x3f;
                                                break;
                                        }
                                }
                        }
                        /* else: continue flag-hunting */
                } else if (likely(seqlen < 5 && trail1 < 7)) {
                        /* streamlined case: 8 data bits, no stuffing */
                        inbyte |= c << inbits;
                        hdlc_putbyte(inbyte & 0xff, bcs);
                        inputstate |= INS_have_data;
                        inbyte >>= 8;
                        /* inbits unchanged */
                } else if (likely(seqlen == 6 && inbits == 7 - lead1 &&
                                  trail1 + 1 == inbits &&
                                  !(inputstate & INS_have_data))) {
                        /* streamlined case: flag idle - state unchanged */
                } else if (unlikely(seqlen > 6)) {
                        /* abort sequence */
                        ubc->aborts++;
                        hdlc_flush(bcs);
                        inputstate |= INS_flag_hunt;
                } else if (seqlen == 6) {
                        /* closing flag, including (6 - lead1) '1's
                         * and one '0' from inbits */
                        if (inbits > 7 - lead1) {
                                hdlc_frag(bcs, inbits + lead1 - 7);
                                inputstate &= ~INS_have_data;
                        } else {
                                if (inbits < 7 - lead1)
                                        ubc->stolen0s++;
                                if (inputstate & INS_have_data) {
                                        hdlc_done(bcs);
                                        inputstate &= ~INS_have_data;
                                }
                        }

                        if (c == PPP_FLAG) {
                                /* complete flag, LSB overlaps preceding flag */
                                ubc->shared0s++;
                                inbits = 0;
                                inbyte = 0;
                        } else if (trail1 != 7) {
                                /* remaining bits */
                                inbyte = c >> (lead1 + 1);
                                inbits = 7 - lead1;
                                if (trail1 >= 8) {
                                        /* interior stuffing:
                                         * omitting the MSB handles most cases,
                                         * correct the incorrectly handled
                                         * cases individually */
                                        inbits--;
                                        switch (c) {
                                        case 0xbe:
                                                inbyte = 0x3f;
                                                break;
                                        }
                                }
                        } else {
                                /* abort sequence follows,
                                 * skb already empty anyway */
                                ubc->aborts++;
                                inputstate |= INS_flag_hunt;
                        }
                } else { /* (seqlen < 6) && (seqlen == 5 || trail1 >= 7) */

                        if (c == PPP_FLAG) {
                                /* complete flag */
                                if (seqlen == 5)
                                        ubc->stolen0s++;
                                if (inbits) {
                                        hdlc_frag(bcs, inbits);
                                        inbits = 0;
                                        inbyte = 0;
                                } else if (inputstate & INS_have_data)
                                        hdlc_done(bcs);
                                inputstate &= ~INS_have_data;
                        } else if (trail1 == 7) {
                                /* abort sequence */
                                ubc->aborts++;
                                hdlc_flush(bcs);
                                inputstate |= INS_flag_hunt;
                        } else {
                                /* stuffed data */
                                if (trail1 < 7) { /* => seqlen == 5 */
                                        /* stuff bit at position lead1,
                                         * no interior stuffing */
                                        unsigned char mask = (1 << lead1) - 1;
                                        c = (c & mask) | ((c & ~mask) >> 1);
                                        inbyte |= c << inbits;
                                        inbits += 7;
                                } else if (seqlen < 5) { /* trail1 >= 8 */
                                        /* interior stuffing:
                                         * omitting the MSB handles most cases,
                                         * correct the incorrectly handled
                                         * cases individually */
                                        switch (c) {
                                        case 0xbe:
                                                c = 0x7e;
                                                break;
                                        }
                                        inbyte |= c << inbits;
                                        inbits += 7;
                                } else { /* seqlen == 5 && trail1 >= 8 */

                                        /* stuff bit at lead1 *and* interior
                                         * stuffing -- unstuff individually */
                                        switch (c) {
                                        case 0x7d:
                                                c = 0x3f;
                                                break;
                                        case 0xbe:
                                                c = 0x3f;
                                                break;
                                        case 0x3e:
                                                c = 0x1f;
                                                break;
                                        case 0x7c:
                                                c = 0x3e;
                                                break;
                                        }
                                        inbyte |= c << inbits;
                                        inbits += 6;
                                }
                                if (inbits >= 8) {
                                        inbits -= 8;
                                        hdlc_putbyte(inbyte & 0xff, bcs);
                                        inputstate |= INS_have_data;
                                        inbyte >>= 8;
                                }
                        }
                }
                seqlen = trail1 & 7;
        }

        /* save new state */
        bcs->inputstate = inputstate;
        ubc->seqlen = seqlen;
        ubc->inbyte = inbyte;
        ubc->inbits = inbits;
}

/* trans_receive
 * pass on received USB frame transparently as SKB via gigaset_skb_rcvd
 * invert bytes
 * tally frames, errors etc. in BC structure counters
 * parameters:
 *      src     received data
 *      count   number of received bytes
 *      bcs     receiving B channel structure
 */
static inline void trans_receive(unsigned char *src, unsigned count,
                                 struct bc_state *bcs)
{
        struct sk_buff *skb;
        int dobytes;
        unsigned char *dst;

        if (unlikely(bcs->ignore)) {
                bcs->ignore--;
                return;
        }
        skb = bcs->rx_skb;
        if (skb == NULL) {
                skb = gigaset_new_rx_skb(bcs);
                if (skb == NULL)
                        return;
        }
        dobytes = bcs->rx_bufsize - skb->len;
        while (count > 0) {
                dst = skb_put(skb, count < dobytes ? count : dobytes);
                while (count > 0 && dobytes > 0) {
                        *dst++ = bitrev8(*src++);
                        count--;
                        dobytes--;
                }
                if (dobytes == 0) {
                        dump_bytes(DEBUG_STREAM_DUMP,
                                   "rcv data", skb->data, skb->len);
                        bcs->hw.bas->goodbytes += skb->len;
                        gigaset_skb_rcvd(bcs, skb);
                        skb = gigaset_new_rx_skb(bcs);
                        if (skb == NULL)
                                return;
                        dobytes = bcs->rx_bufsize;
                }
        }
}

void gigaset_isoc_receive(unsigned char *src, unsigned count,
                          struct bc_state *bcs)
{
        switch (bcs->proto2) {
        case L2_HDLC:
                hdlc_unpack(src, count, bcs);
                break;
        default:                /* assume transparent */
                trans_receive(src, count, bcs);
        }
}

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

/* process a block of received bytes in command mode (mstate != MS_LOCKED)
 * Append received bytes to the command response buffer and forward them
 * line by line to the response handler.
 * Note: Received lines may be terminated by CR, LF, or CR LF, which will be
 * removed before passing the line to the response handler.
 */
static void cmd_loop(unsigned char *src, int numbytes, struct inbuf_t *inbuf)
{
        struct cardstate *cs = inbuf->cs;
        unsigned cbytes      = cs->cbytes;
        unsigned char c;

        while (numbytes--) {
                c = *src++;
                switch (c) {
                case '\n':
                        if (cbytes == 0 && cs->respdata[0] == '\r') {
                                /* collapse LF with preceding CR */
                                cs->respdata[0] = 0;
                                break;
                        }
                        /* fall through */
                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;
                        break;
                default:
                        /* append to line buffer if possible */
                        if (cbytes < MAX_RESP_SIZE)
                                cs->respdata[cbytes] = c;
                        cbytes++;
                }
        }

        /* save state */
        cs->cbytes = cbytes;
}


/* process a block of data received through the control channel
 */
void gigaset_isoc_input(struct inbuf_t *inbuf)
{
        struct cardstate *cs = inbuf->cs;
        unsigned tail, head, numbytes;
        unsigned char *src;

        head = inbuf->head;
        while (head != (tail = inbuf->tail)) {
                gig_dbg(DEBUG_INTR, "buffer state: %u -> %u", head, tail);
                if (head > tail)
                        tail = RBUFSIZE;
                src = inbuf->data + head;
                numbytes = tail - head;
                gig_dbg(DEBUG_INTR, "processing %u bytes", numbytes);

                if (cs->mstate == MS_LOCKED) {
                        gigaset_dbg_buffer(DEBUG_LOCKCMD, "received response",
                                           numbytes, src);
                        gigaset_if_receive(inbuf->cs, src, numbytes);
                } else {
                        cmd_loop(src, numbytes, inbuf);
                }

                head += numbytes;
                if (head == RBUFSIZE)
                        head = 0;
                gig_dbg(DEBUG_INTR, "setting head to %u", head);
                inbuf->head = head;
        }
}


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

/**
 * gigaset_isoc_send_skb() - queue an skb for sending
 * @bcs:        B channel descriptor structure.
 * @skb:        data to send.
 *
 * Called by LL to 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. -ENODEV) on error
 */
int gigaset_isoc_send_skb(struct bc_state *bcs, struct sk_buff *skb)
{
        int len = skb->len;
        unsigned long flags;

        spin_lock_irqsave(&bcs->cs->lock, flags);
        if (!bcs->cs->connected) {
                spin_unlock_irqrestore(&bcs->cs->lock, flags);
                return -ENODEV;
        }

        skb_queue_tail(&bcs->squeue, skb);
        gig_dbg(DEBUG_ISO, "%s: skb queued, qlen=%d",
                __func__, skb_queue_len(&bcs->squeue));

        /* tasklet submits URB if necessary */
        tasklet_schedule(&bcs->hw.bas->sent_tasklet);
        spin_unlock_irqrestore(&bcs->cs->lock, flags);

        return len;     /* ok so far */
}