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Date:   Wed, 24 Apr 2019 11:24:52 +0200
From:   Thomas Jarosch <>
To:     Arnd Bergmann <>
Cc:     Karsten Keil <>,,
        Tilman Schmidt <>,
        Paul Bolle <>,,,
        Al Viro <>,
        Holger Schurig <>
Subject: Re: [PATCH 5/5] isdn: move capi drivers to staging

Hello Arnd,

You wrote on Tue, Apr 23, 2019 at 05:11:43PM +0200:
> I tried to find any indication of whether the capi drivers are
> still in use, and have not found anything  from a long time ago.
> With public ISDN networks almost completely shut down over the past 12
> months, there is very little you can actually do with this hardware. The
> main remaining use case would be to connect ISDN voice phones to an
> in-house installation with Asterisk or LCR, but anyone trying this in
> turn seems to be using either the mISDN driver stack, or out-of-tree
> drivers from the hardware vendors.
> I may of course have missed something, so I would suggest moving
> these into drivers/staging/ just in case someone still uses one
> of the three remaining in-kernel drivers (avm, hysdn, gigaset).
> If nobody complains, we can remove them entirely in six months,
> or otherwise move the core code and any drivers that are still
> needed back into drivers/isdn.

thanks for your isdn4linux cleanup work!

AFAIK the base capi drivers are still needed for mISDN, too.
I quickly checked a machine that uses mISDNcapid for receiving fax
and the modules "capi" and "kernelcapi" are loaded.

# lsmod |grep capi
capi                   10751  2
kernelcapi             33675  1 capi

# capiinfo
Number of Controllers : 1
Controller 1:
Manufacturer: mISDN
CAPI Version: 2.0
Manufacturer Version: 0.1
Serial Number: 0000001
BChannels: 2
Global Options: 0x00000001
   internal controller supported
B1 protocols support: 0x00000013
   64 kbit/s with HDLC framing
   64 kbit/s bit-transparent operation
   T.30 modem for fax group 3
B2 protocols support: 0x00000013
   ISO 7776 (X.75 SLP)
   T.30 for fax group 3
B3 protocols support: 0x00000031
   T.30 for fax group 3
   T.30 for fax group 3 with extensions

  00000000 00000000 00000000 00000000 00000000 00000000
  00000000 00000000 00000000 00000000 00000000

Supplementary services support: 0x00000000

-> I think the CAPI layer is still needed, but Karsten knows best.

The ISDN network of Deutsche Telekom in Germany is still
*in the process* of being shut down, business customers that use
"direct inward dialing" (DID / "Anlagenanschlu├č") often still use ISDN.
For example we use it here at the office, but preparations for
a SIP migration are being done.

Vodafone Germany guarantees business customers to support ISDN until 2022.

Quite a few people use a SIP -> ISDN converter like the Fritz!Box or LANCOM 
routers to keep their fax machines running. It's a bit crazy, but people seem
to love it. We deal with this on a weekly basis to support
our customers during the migration period.

Intra2net is currently in the process of upgrading to kernel 4.19.x
and Karsten recently did all the necessary adaptions for mISDN.
So the ISDN code is used with modern (LTS) kernels ^^

Best regards,
Thomas Jarosch

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