Modem Manager Locks Dual FTDI Serial Ports

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ModemManager 0.6.x supports RS232 modems connected to the host through a serial-usb adapter. This patch would make those modems stop working, so I don't think this should be applied to git master or any other distro.

ModemManager shouldn't grab those tty ports for that long. The problem here is that given that the connection is through a serial<->usb converter, udev gives us information about the converter, so we can only know that the modem is a serial modem by probing the ports. The fact that it takes so long in each port is because the probing in 0.6 tries to do a lot of things on ports which may not be AT ports. In MM 0.7+ this probing in each port should really take much much less.

As for the single FTDI USB-serial converter being completely blacklisted; I think it shouldn't be.

A wise change would be to fully skip probing these ports in MM unless the user asks for it through the Scan() method. That would require to remove all the usb<->serial converters from the blacklist, and only have them probed through manually launched Scan()s, not by the initial automatic port probing.

Are there any modems using a FT2232 chip without a custom USB device ID? I suggested the change on the basis that the chip is commonly used in embedded devices (e.g. http://www.tincantools.com/product.php?productid=16134 and https://www.gumstix.com/store/product_info.php?products_id=262) without the extra eeprom used to set a custom VID/PID but expected (perhaps naively) that modem designers would actually want a unique identifier for their particular device. I certainly understand dropping the patch if there are Modem out there that would be broken by this change.

This is good to hear that the probe will be shorter in future versions and avoiding automatic probing seems like a good change :).

Modems won't be using the FT2232 chip directly but serial adapters will. Imagine this setup:

PC[USB] <---> USB to RS232 adapter <---> [RS232]Modem

The only way for ModemManager to know that there is a modem behind the adapter is to probe the port.

Oh, it seems that the single FTDI USB<->serial converter is blacklisted only in IUbuntu:
http://bazaar.launchpad.net/~ubuntu-branches/ubuntu/raring/modemmanager/raring/view/head:/debian/patches/arduino-blacklist.patch

I'll let Ubuntu packagers to comment then :)

Ahh---that makes sense about the USB to Serial adapter--thanks for explaining Alekasander.

As a USB-to-serial adapter is a generic device that may or may not be connected to a modem, a manually-launched scan makes sense. In the interim though, it makes sense that distros adjust the blacklist to fit their user base.

Ack.

We already blacklist specific devices, and it seems as though this particular one is indeed used for things other than modems. It remains that it's easy enough to remove/comment out the blacklist entry, and I still live in my fantasy world where RS232 modem users are becoming more rare.

We'll revisit and drop these blacklist patches as soon as we can land MM 0.7.

Assigning to me because I'll need to include the patch at some point; but it's waiting until I can finish up an update for NM in Raring.

I opened a new bug upstream to track the root issue:
https://bugzilla.gnome.org/show_bug.cgi?id=691076

This also affects FTDI's newer FT230X series. VID:0403, PID:6015