path: root/drivers/isdn/gigaset/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)
{
	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;
	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 = 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;
	}
	gig_dbg(DEBUG_ISO,
		"%s: acquired iso write semaphore, data[write]=%02x, nbits=%d",
		__func__, iwb->data[iwb->write], iwb->wbits);
	return 1;
}

/* 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;
	}
	src = iwb->read;
	if (unlikely(limit >= BAS_OUTBUFSIZE + BAS_OUTBUFPAD ||
		     (read < src && limit >= src))) {
		pr_err("isoc write buffer frame reservation violated\n");
		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 */
			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)) {
		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 iwb->write;

	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 = 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 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 = 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 {
			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);
		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 */
}