[systemd-devel] WebUSB

Wed Jan 11 15:31:02 UTC 2017

On Wed, 2017-01-11 at 16:01 +0100, Lars Knudsen wrote:
> If it can be invoked via DBus - what is the harm to only do the scan
> for
> the greylisted (in this case webusb) modems when the user actually
> wants to
> search for a modem (like a printer) - and leave the poor devices
> alone
> otherwise?  In headless systems, it will not be the same problem as
> they
> will most probably be custom made anyway.

Yes, headless/embedded/industrial systems are fairly easy as they are
well controlled.  Desktop-type use-cases expect things to just work
when plugged in, but modem (and USB device in general) OEMs are a
contrary bunch and often don't bother to identify their devices in a
way that lets them be used easily by the OS.

I'd love a magic "this is a modem!" descriptor, but we don't have one
and never will.  While I don't want to get into a huge UI discussion,
unless devices are network connected, searching isn't the normal way
devices get found.  They get plugged in, and they just work.  And we
get to figure out all the details like this :)

Related question though; if it's a webusb modem or even a cdc-acm
device, is the issue the *time* taken by probing, or the AT/DM requests
themselves?  Most devices I know of (modem or not) will disregard
communication they don't know about as a function of their protocol. 
MM's probe process does not alter device state in any way, just
requests informational responses.

Dan

> On Wed, Jan 11, 2017 at 3:32 PM, Dan Williams <dcbw at redhat.com>
> wrote:
> 
> > On Wed, 2017-01-11 at 14:21 +0100, Christer Weinigel wrote:
> > > On 2017-01-10 19:55, Lars Knudsen wrote:
> > > > On Tue, Jan 10, 2017 at 7:08 PM, Dan Williams <dcbw at redhat.com
> > > > <mailto:dcbw at redhat.com>> wrote:
> > > >     And we're quite happy to keep blacklisting specific VID/PID
> > > > combos we
> > > >     know are not modems. Another possible solution is to
> > > > greylist
> > > > devices
> > > >     that happen to have webusb descriptors, such that they
> > > > won't
> > > > get auto-
> > > >     probed, but could be probed on-demand via D-Bus.  But I'd
> > > > rather that
> > > >     happen via udev rules than MM trying to walk USB device
> > > > attributes and
> > > >     parsing webusb descriptors.
> > > > 
> > > > Actually, that sounds like a very good compromise.  I remember
> > > > my
> > > > own
> > > > struggles 3-4 years ago when I had to get a device working
> > > > properly
> > > > on
> > > > ChromeOS and Ubuntu, where the firmware had to handle that the
> > > > first ~16
> > > > seconds it would *sometimes* get sent strange AT commands (the
> > > > probing)
> > > > all while the system thought it could already start speaking
> > > > with
> > > > the
> > > > device over e.g. chrome.serial.  Eventually you (modemmanager)
> > > > were
> > > > kind
> > > > enough to get our VID/PID listed and ChromeOS was quick to pick
> > > > it
> > > > up
> > > > (~5-6 months to get in stable) and ubuntu so kind to upgrade to
> > > > the
> > > > version of modemmanager including our blacklisting approx 2.5
> > > > years
> > > > later (sigh) ;)
> > > 
> > > Weird question: should modem manager really autoprobe _every_
> > > serial
> > > device nowdays?  99% of the devices I connect to my laptop are
> > > not
> > > modems.  They are serial ports on development platforms, RS485
> > > interfaces, Arduinos with a FTDI, CP210x or CH341 USB-UART
> > > bridge,
> > > and
> > > so on.  Modems with a physical serial port are almost nonexistent
> > > today.
> > >  For me it's a pain in the back to have to update the blacklist
> > > of
> > > things modem manger shouldn't touch.
> > 
> > MM does already whitelist platform serial devices (eg, i8250 UART)
> > and
> > already greylists USB<->serial adapters like FTDI and CP210x.
> > 
> > Unfortunately, you'd be surprised how many modems actually *do* get
> > hooked up with USB<->serial converters like FTDI and CP210x.  Modem
> > manufacturers often build these chips into devices so the modem
> > looks
> > like USB but uses a generic VID/PID and a generic driver (FTDI).
> > 
> > If you have updates to the blacklist, we'd happily take them.
> > 
> > > Wouldn't it be better to whitelist known ḿodems and have modem
> > > manager
> > > ignore everything else?  Devices which are so new that modem
> > > manager
> > > don't know about them can be configured manually.
> > 
> > I ran a list of explicit modem VID/PID pairs in kernel drivers
> > (like
> > option, qmi_wwan, sierra, hso, etc) 2 years ago and there were
> > >1000
> > known WWAN modems.
> > 
> > That >1000 does *not* count attribute-matched devices like CDC ACM
> > devices, CDC WDM/ether, generic serial bridge modems (FTDI/CP210x),
> > or
> > USB interface class/subclass/protocol matching which many Huawei
> > devices now use instead.  Whitelisting is simply not really an
> > option,
> > unfortunately, as too many new modem devices actually do come out
> > every
> > year.  Thankfully, many these days are MBIM (thanks to Windows 8+)
> > or
> > QMI, but the embedded world still does a lot of serially-bridged
> > devices.
> > 
> > Dan
> > 
> > > At least to me that seems like a much more sane default.
> > > 
> > >   /Christer
> > > _______________________________________________
> > > ModemManager-devel mailing list
> > > ModemManager-devel at lists.freedesktop.org
> > > https://lists.freedesktop.org/mailman/listinfo/modemmanager-devel