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isocdata.c

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

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

/* initialize buffer structure
 */
void gigaset_isowbuf_init(struct isowbuf_t *iwb, unsigned char idle)
{
      atomic_set(&iwb->read, 0);
      atomic_set(&iwb->nextread, 0);
      atomic_set(&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 = atomic_read(&iwb->read);
      write = atomic_read(&iwb->write);
      if ((freebytes = read - write) > 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;
      }
}

/* compare two offsets within the buffer
 * The buffer is seen as circular, with the read position as start
 * returns -1/0/1 if position a </=/> position b without crossing 'read'
 */
static inline int isowbuf_poscmp(struct isowbuf_t *iwb, int a, int b)
{
      int read;
      if (a == b)
            return 0;
      read = atomic_read(&iwb->read);
      if (a < b) {
            if (a < read && read <= b)
                  return +1;
            else
                  return -1;
      } else {
            if (b < read && read <= a)
                  return -1;
            else
                  return +1;
      }
}

/* start writing
 * acquire the write semaphore
 * return true if acquired, false 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 0;
      }
#ifdef CONFIG_GIGASET_DEBUG
      gig_dbg(DEBUG_ISO,
            "%s: acquired iso write semaphore, data[write]=%02x, nbits=%d",
            __func__, iwb->data[atomic_read(&iwb->write)], iwb->wbits);
#endif
      return 1;
}

/* finish writing
 * release the write semaphore and update the maximum buffer fill level
 * returns the current write position
 */
static inline int isowbuf_donewrite(struct isowbuf_t *iwb)
{
      int write = atomic_read(&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 = atomic_read(&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;
      atomic_set(&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 = atomic_read(&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 = atomic_read(&iwb->nextread);
      write = atomic_read(&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)) {
            err("invalid size %d", size);
            return -EINVAL;
      }
      src = atomic_read(&iwb->read);
      if (unlikely(limit > BAS_OUTBUFSIZE + BAS_OUTBUFPAD ||
                 (read < src && limit >= src))) {
            err("isoc write buffer frame reservation violated");
            return -EFAULT;
      }
#endif

      if (read < write) {
            /* no wraparound in valid data */
            if (limit >= write) {
                  /* append idle frame */
                  if (!isowbuf_startwrite(iwb))
                        return -EBUSY;
                  /* write position could have changed */
                  if (limit >= (write = atomic_read(&iwb->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 */
                        atomic_set(&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;
            }
      }
      atomic_set(&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];
      static const char hexdigit[] = "0123456789abcdef";
      int i = 0;
      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++] = hexdigit[(c >> 4) & 0x0f];
            dbgline[i++] = hexdigit[c & 0x0f];
      }
      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)) {
            gig_dbg(DEBUG_ISO, "%s: %d bytes free -> -EAGAIN",
                  __func__, isowbuf_freebytes(iwb));
            return -EAGAIN;
      }

      dump_bytes(DEBUG_STREAM, "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);
      dump_bytes(DEBUG_STREAM_DUMP, "isowbuf", iwb->data, end + 1);
      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 atomic_read(&iwb->write); /* better ideas? */

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

      gig_dbg(DEBUG_STREAM, "put %d bytes", count);
      write = atomic_read(&iwb->write);
      do {
            c = bitrev8(*in++);
            iwb->data[write++] = c;
            write %= BAS_OUTBUFSIZE;
      } while (--count > 0);
      atomic_set(&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 ISDN_PROTO_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->fcs = crc_ccitt_byte(bcs->fcs, c);
      if (unlikely(bcs->skb == NULL)) {
            /* skipping */
            return;
      }
      if (unlikely(bcs->skb->len == SBUFSIZE)) {
            dev_warn(bcs->cs->dev, "received oversized packet discarded\n");
            bcs->hw.bas->giants++;
            dev_kfree_skb_any(bcs->skb);
            bcs->skb = NULL;
            return;
      }
      *__skb_put(bcs->skb, 1) = 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 (likely(bcs->skb != NULL))
            skb_trim(bcs->skb, 0);
      else if (!bcs->ignore) {
            if ((bcs->skb = dev_alloc_skb(SBUFSIZE + HW_HDR_LEN)) != NULL)
                  skb_reserve(bcs->skb, HW_HDR_LEN);
            else
                  dev_err(bcs->cs->dev, "could not allocate skb\n");
      }

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

/* hdlc_done
 * process completed HDLC data packet
 */
static inline void hdlc_done(struct bc_state *bcs)
{
      struct sk_buff *procskb;

      if (unlikely(bcs->ignore)) {
            bcs->ignore--;
            hdlc_flush(bcs);
            return;
      }

      if ((procskb = bcs->skb) == NULL) {
            /* previous error */
            gig_dbg(DEBUG_ISO, "%s: skb=NULL", __func__);
            gigaset_rcv_error(NULL, bcs->cs, bcs);
      } else if (procskb->len < 2) {
            dev_notice(bcs->cs->dev, "received short frame (%d octets)\n",
                     procskb->len);
            bcs->hw.bas->runts++;
            gigaset_rcv_error(procskb, bcs->cs, bcs);
      } else if (bcs->fcs != PPP_GOODFCS) {
            dev_notice(bcs->cs->dev, "frame check error (0x%04x)\n",
                     bcs->fcs);
            bcs->hw.bas->fcserrs++;
            gigaset_rcv_error(procskb, bcs->cs, bcs);
      } else {
            procskb->len -= 2;            /* subtract FCS */
            procskb->tail -= 2;
            gig_dbg(DEBUG_ISO, "%s: good frame (%d octets)",
                  __func__, procskb->len);
            dump_bytes(DEBUG_STREAM,
                     "rcv data", procskb->data, procskb->len);
            bcs->hw.bas->goodbytes += procskb->len;
            gigaset_rcv_skb(procskb, bcs->cs, bcs);
      }

      if ((bcs->skb = dev_alloc_skb(SBUFSIZE + HW_HDR_LEN)) != NULL)
            skb_reserve(bcs->skb, HW_HDR_LEN);
      else
            dev_err(bcs->cs->dev, "could not allocate skb\n");
      bcs->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_rcv_error(bcs->skb, bcs->cs, bcs);

      if ((bcs->skb = dev_alloc_skb(SBUFSIZE + HW_HDR_LEN)) != NULL)
            skb_reserve(bcs->skb, HW_HDR_LEN);
      else
            dev_err(bcs->cs->dev, "could not allocate skb\n");
      bcs->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_rcv_skb
 * notify of errors via gigaset_rcv_error
 * 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 */
                              inbits--;
                              /* correct the incorrectly handled cases individually */
                              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 */
                              inbits--;
                              /* correct the incorrectly handled cases individually */
                              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 */
                              switch (c) {      /* unstuff individually */
                              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_rcv_skb
 * 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--;
            hdlc_flush(bcs);
            return;
      }
      if (unlikely((skb = bcs->skb) == NULL)) {
            bcs->skb = skb = dev_alloc_skb(SBUFSIZE + HW_HDR_LEN);
            if (!skb) {
                  dev_err(bcs->cs->dev, "could not allocate skb\n");
                  return;
            }
            skb_reserve(skb, HW_HDR_LEN);
      }
      bcs->hw.bas->goodbytes += skb->len;
      dobytes = TRANSBUFSIZE - 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) {
                  gigaset_rcv_skb(skb, bcs->cs, bcs);
                  bcs->skb = skb = dev_alloc_skb(SBUFSIZE + HW_HDR_LEN);
                  if (!skb) {
                        dev_err(bcs->cs->dev,
                              "could not allocate skb\n");
                        return;
                  }
                  skb_reserve(bcs->skb, HW_HDR_LEN);
                  dobytes = TRANSBUFSIZE;
            }
      }
}

void gigaset_isoc_receive(unsigned char *src, unsigned count, struct bc_state *bcs)
{
      switch (bcs->proto2) {
      case ISDN_PROTO_L2_HDLC:
            hdlc_unpack(src, count, bcs);
            break;
      default:          /* assume transparent */
            trans_receive(src, count, bcs);
      }
}

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

static void cmd_loop(unsigned char *src, int numbytes, struct inbuf_t *inbuf)
{
      struct cardstate *cs = inbuf->cs;
      unsigned cbytes      = cs->cbytes;

      while (numbytes--) {
            /* copy next character, check for end of line */
            switch (cs->respdata[cbytes] = *src++) {
            case '\r':
            case '\n':
                  /* end of line */
                  gig_dbg(DEBUG_TRANSCMD, "%s: End of Command (%d Bytes)",
                        __func__, cbytes);
                  if (cbytes >= MAX_RESP_SIZE - 1)
                        dev_warn(cs->dev, "response too large\n");
                  cs->cbytes = cbytes;
                  gigaset_handle_modem_response(cs);
                  cbytes = 0;
                  break;
            default:
                  /* advance in line buffer, checking for overflow */
                  if (cbytes < MAX_RESP_SIZE - 1)
                        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 = atomic_read(&inbuf->head);
      while (head != (tail = atomic_read(&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 (atomic_read(&cs->mstate) == MS_LOCKED) {
                  gigaset_dbg_buffer(DEBUG_LOCKCMD, "received response",
                                 numbytes, src);
                  gigaset_if_receive(inbuf->cs, src, numbytes);
            } else {
                  gigaset_dbg_buffer(DEBUG_CMD, "received response",
                                 numbytes, src);
                  cmd_loop(src, numbytes, inbuf);
            }

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


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

/* gigaset_send_skb
 * called by common.c to queue an skb for sending
 * and start transmission if necessary
 * parameters:
 *    B Channel control structure
 *    skb
 * return value:
 *    number of bytes accepted for sending
 *    (skb->len if ok, 0 if out of buffer space)
 *    or error code (< 0, eg. -EINVAL)
 */
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 */
}

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