Date:   Thu, 25 Apr 2019 13:24:09 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Thomas Jarosch <thomas.jarosch@...ra2net.com>
Cc:     Karsten Keil <isdn@...ux-pingi.de>,
        Networking <netdev@...r.kernel.org>,
        Tilman Schmidt <tilman@...p.cc>,
        Paul Bolle <pebolle@...cali.nl>,
        gigaset307x-common@...ts.sourceforge.net,
        isdn4linux@...tserv.isdn4linux.de,
        Al Viro <viro@...iv.linux.org.uk>,
        Holger Schurig <holgerschurig@...glemail.com>
Subject: Re: [PATCH 5/5] isdn: move capi drivers to staging

On Wed, Apr 24, 2019 at 3:06 PM Thomas Jarosch
<thomas.jarosch@...ra2net.com> wrote:
>
> Hi Arnd,
>
> > Ok, interesting. My understanding was that mISDN CAPI support
> > was done purely in user space, on top of the mISDN interface.
> >
> > I don't see any interfaction between the two in the kernel code,
> > but if the capi module is required for mISDN, we clearly have to
> > keep it. We could still move the avm/gigaset/hysdn/cmtp drivers
> > to staging though, if there are no users for those.
>
> AVM Fritz!PCI cards are supported by the mISDN subsystem anyway,
> the new driver is "avmfritz" and used by us in production.
>
> > Right, this is what I'm trying to find out here. I realize that there
> > are (very few) remaining users of ISDN voice services, but this only
> > matters if someone uses them
> >
> > 1. with a modern Linux kernel, and planning to upgrade beyond linux-5.3
> > 2. with a device driver that ships with the kernel
> > 3. using the CAPI subsystem
> >
> > I suspect that all three of the above are true in isolation, but onless
> > at least one person needs all three combined, that doesn't stop us
> > from staging them out.
>
> 1. + 3. applies to us. The mISDN drivers are based on the kernel ones,
> but maintained in an extra git tree on top of the kernel. The situation
> is not ideal but that's what it currently is. git repo:
> https://github.com/ISDN4Linux/mISDN

I'm still confused by this: You say here that you use the CAPI
subsystem from the mainline kernel (i.e. /dev/capi20 rather
than mISDNcapid), but this does not appear to interact at all with
mISDN, neither the in-kernel variant nor the one you link to.

> > That leaves the question of whether there is anyone rolling their
> > own routers and/or fax machines based on future kernels with the
> > avm/gigaset/hysdn/cmtp CAPI drivers, and which drivers in particular
> > that would be.
>
> I would guess that isdn4linux is mostly dead and the drivers
> can be moved to staging.

I'd still prefer to remove isdn4linux+hisax completely and
only take CAPI+avm/gigaset/hysdn into staging.
My original suggestion was to move all of it to staging, but if we
keep cmtp in the tree, then at least the CAPI core has to stay
as well.

> I didn't encounter cmtp (ISDN over Bluetooth) in real life yet.
> Intra2net uses mISDN v2 only and software fax support in mISDNcapid was
> developed because of us, so I guess we are the main user, too.

> [funny side note: I use a 4 port Eicon diva card at home for my SIP
> -> ISDN gateway. The eicon driver just got removed, too, but it still works
> fine on Centos 7.x 3.10 kernels. Though this is an exotic use case and I would not
> NAK the removal of the driver since the kernel maintenance costs
> don't justify it. If it stops getting supported, I'll either set up
> something based on mISDNv2 + LCR or get a used Fritz!Box for this task.]

There seems to also be a third-party driver for the Divas:
https://www.dialogic.com/downloads/diva/diva%20sr%20linux

I think this is what most others that still have such hardware use,
and has been the case for a while.

        Arnd

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