We have not heard any activities from Karsten in years:

  - Last review tag was nine years ago in commit a921e9bd4e22a7
    ("isdn: i4l: move active-isdn drivers to staging")
  - Last message on lore was in October 2020 [1].

Furthermore, messages to isdn mailing list bounce.

Mark the subsystem as orphan to reflect these.

[1]: https://lore.kernel.org/all/0ee243a9-9937-ad26-0684-44b18e772662@linux-pingi.de/

Signed-off-by: Bagas Sanjaya <bagasdotme@gmail.com>
---
netdev maintainers: I have sent request message to Karsten off-list prior to
sending this patch. Please hold off applying it until a week later when I
will inform whether he responds or not.

 CREDITS     | 4 ++++
 MAINTAINERS | 8 ++------
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/CREDITS b/CREDITS
index 903ea238e64f3c..fa5397f4ebcdd0 100644
--- a/CREDITS
+++ b/CREDITS
@@ -2036,6 +2036,10 @@ S: Botanicka' 68a
 S: 602 00 Brno
 S: Czech Republic
 
+N: Karsten Keil
+E: isdn@linux-pingi.de
+D: ISDN subsystem maintainer
+
 N: Jakob Kemi
 E: jakob.kemi@telia.com
 D: V4L W9966 Webcam driver
diff --git a/MAINTAINERS b/MAINTAINERS
index 545a4776795e67..8d2dbb07c44099 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -13246,10 +13246,8 @@ T:	git git://git.kernel.org/pub/scm/linux/kernel/git/nab/target-pending.git mast
 F:	drivers/infiniband/ulp/isert
 
 ISDN/CMTP OVER BLUETOOTH
-M:	Karsten Keil <isdn@linux-pingi.de>
-L:	isdn4linux@listserv.isdn4linux.de (subscribers-only)
 L:	netdev@vger.kernel.org
-S:	Odd Fixes
+S:	Orphan
 W:	http://www.isdn4linux.de
 F:	Documentation/isdn/
 F:	drivers/isdn/capi/
@@ -13258,10 +13256,8 @@ F:	include/uapi/linux/isdn/
 F:	net/bluetooth/cmtp/
 
 ISDN/mISDN SUBSYSTEM
-M:	Karsten Keil <isdn@linux-pingi.de>
-L:	isdn4linux@listserv.isdn4linux.de (subscribers-only)
 L:	netdev@vger.kernel.org
-S:	Maintained
+S:	Orphan
 W:	http://www.isdn4linux.de
 F:	drivers/isdn/Kconfig
 F:	drivers/isdn/Makefile

base-commit: c0178eec8884231a5ae0592b9fce827bccb77e86
-- 
An old man doll... just what I always wanted! - Clara

On Thu, Oct 23, 2025 at 04:24:06PM +0700, Bagas Sanjaya wrote:
> We have not heard any activities from Karsten in years:
> 
>   - Last review tag was nine years ago in commit a921e9bd4e22a7
>     ("isdn: i4l: move active-isdn drivers to staging")
>   - Last message on lore was in October 2020 [1].
> 
> Furthermore, messages to isdn mailing list bounce.
> 
> Mark the subsystem as orphan to reflect these.
> 
> [1]: https://lore.kernel.org/all/0ee243a9-9937-ad26-0684-44b18e772662@linux-pingi.de/
> 
> Signed-off-by: Bagas Sanjaya <bagasdotme@gmail.com>
> ---
> netdev maintainers: I have sent request message to Karsten off-list prior to
> sending this patch. Please hold off applying it until a week later when I
> will inform whether he responds or not.

FTR, I checked the information in the commit message,
and my searches match what is written above.

I agree waiting a week is a good plan.

Reviewed-by: Simon Horman <horms@kernel.org>

On Mon, Oct 27, 2025 at 07:28:55PM +0000, Simon Horman wrote:
> On Thu, Oct 23, 2025 at 04:24:06PM +0700, Bagas Sanjaya wrote:
> > netdev maintainers: I have sent request message to Karsten off-list prior to
> > sending this patch. Please hold off applying it until a week later when I
> > will inform whether he responds or not.
> <snipped>...
> I agree waiting a week is a good plan.

Indeed because Karsten does not reply to my inquiry (he's MIA).

Thanks. 

-- 
An old man doll... just what I always wanted! - Clara