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;
	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 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