v4.19.13 snapshot.
diff --git a/include/linux/isdn/hdlc.h b/include/linux/isdn/hdlc.h
new file mode 100644
index 0000000..9652137
--- /dev/null
+++ b/include/linux/isdn/hdlc.h
@@ -0,0 +1,82 @@
+/*
+ * hdlc.h -- General purpose ISDN HDLC decoder.
+ *
+ * Implementation of a HDLC decoder/encoder in software.
+ * Necessary because some ISDN devices don't have HDLC
+ * controllers.
+ *
+ * Copyright (C)
+ * 2009 Karsten Keil <keil@b1-systems.de>
+ * 2002 Wolfgang Mües <wolfgang@iksw-muees.de>
+ * 2001 Frode Isaksen <fisaksen@bewan.com>
+ * 2001 Kai Germaschewski <kai.germaschewski@gmx.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.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+#ifndef __ISDNHDLC_H__
+#define __ISDNHDLC_H__
+
+struct isdnhdlc_vars {
+ int bit_shift;
+ int hdlc_bits1;
+ int data_bits;
+ int ffbit_shift; /* encoding only */
+ int state;
+ int dstpos;
+
+ u16 crc;
+
+ u8 cbin;
+ u8 shift_reg;
+ u8 ffvalue;
+
+ /* set if transferring data */
+ u32 data_received:1;
+ /* set if D channel (send idle instead of flags) */
+ u32 dchannel:1;
+ /* set if 56K adaptation */
+ u32 do_adapt56:1;
+ /* set if in closing phase (need to send CRC + flag) */
+ u32 do_closing:1;
+ /* set if data is bitreverse */
+ u32 do_bitreverse:1;
+};
+
+/* Feature Flags */
+#define HDLC_56KBIT 0x01
+#define HDLC_DCHANNEL 0x02
+#define HDLC_BITREVERSE 0x04
+
+/*
+ The return value from isdnhdlc_decode is
+ the frame length, 0 if no complete frame was decoded,
+ or a negative error number
+*/
+#define HDLC_FRAMING_ERROR 1
+#define HDLC_CRC_ERROR 2
+#define HDLC_LENGTH_ERROR 3
+
+extern void isdnhdlc_rcv_init(struct isdnhdlc_vars *hdlc, u32 features);
+
+extern int isdnhdlc_decode(struct isdnhdlc_vars *hdlc, const u8 *src,
+ int slen, int *count, u8 *dst, int dsize);
+
+extern void isdnhdlc_out_init(struct isdnhdlc_vars *hdlc, u32 features);
+
+extern int isdnhdlc_encode(struct isdnhdlc_vars *hdlc, const u8 *src,
+ u16 slen, int *count, u8 *dst, int dsize);
+
+#endif /* __ISDNHDLC_H__ */