Merge tag 'isdn-removal' of https://git.kernel.org/pub/scm/linux/kernel/git/arnd/playground

Arnd Bergmann says:

====================
isdn: deprecate non-mISDN drivers

When isdn4linux came up in the context of another patch series, I
remembered that we had discussed removing it a while ago.

It turns out that the suggestion from Karsten Keil wa to remove I4L
in 2018 after the last public ISDN networks are shut down. This has
happened now (with a very small number of exceptions), so I guess it's
time to try again.

We currently have three ISDN stacks in the kernel: the original
isdn4linux (with the hisax driver), the newer CAPI (with four drivers),
and finally the mISDN stack (supporting roughly the same hardware as
hisax).

As far as I can tell, anyone using ISDN with mainline kernel drivers in
the past few years uses mISDN, and this is typically used for voice-only
PBX installations that don't require a public network.

The older stacks support additional features for data networks, but those
typically make no sense any more if there is no network to connect to.

My proposal for this time is to kill off isdn4linux entirely, as it seems
to have been unusable for quite a while. This code has been abandoned
for many years and it does cause problems for treewide maintenance as
it tends to do everything that we try to stop doing.
Birger Harzenetter mentioned that is is still using i4l in order to
make use of the 'divert' feature that is not part of mISDN, but has
otherwise moved on to mISDN for normal operation, like apparently
everyone else.

CAPI in turn is not quite as obsolete, but two of the drivers (avm
and hysdn) don't seem to be used at all, while another one (gigaset)
will stop being maintained as Paul Bolle is no longer able to
test it after the network gets shut down in September.
All three are now moved into drivers/staging to let others speak
up in case there are remaining users.
This leaves Bluetooth CMTP as the only remaining user of CAPI, but
Marcel Holtmann wishes to keep maintaining it.

For the discussion on version 1, see [2]
Unfortunately, Karsten Keil as the maintainer has not participated in
the discussion.

      Arnd

[1] https://patchwork.kernel.org/patch/8484861/#17900371
[2] https://listserv.isdn4linux.de/pipermail/isdn4linux/2019-April/thread.html
====================

Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 69 insertions, 0 deletions

diff --git a/drivers/isdn/hardware/mISDN/isdnhdlc.h b/drivers/isdn/hardware/mISDN/isdnhdlc.h
new file mode 100644
index 000000000000..fe2c1279c139
--- /dev/null
+++ b/drivers/isdn/hardware/mISDN/isdnhdlc.h
@@ -0,0 +1,69 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * 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>
+ */
+
+#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__ */