Attach a GPS in preboot mode

[lnj.sam@gmail.com]

Hello everyone and best wishes for 2023 :)

I have an old *Garmin Drive Smart 50 GPS* and I want to be able to 
attach it when it is in preboot mode to a VM hosted by a *Debian 11 host*.

 From what I understand, the preboot mode allows us to flash a firmware 
before the GPS actually starts (used among other things when the GPS is 
soft bricked).

When I connect the GPS to the host it gives:

|root at host:~# journalctl -kf||
||# GPS in MTP storage mode (default when reset)||
||...||
||janv. 23 23:02:51 host kernel: usb 2-4: New USB device found, 
idVendor=091e, idProduct=48db, bcdDevice= 0.01||
||janv. 23 23:02:51 host kernel: usb 2-4: New USB device strings: Mfr=1, 
Product=2, SerialNumber=5||
||...||
||# GPS in mass storage mode||
||...||
||janv. 23 23:01:29 host kernel: usb 2-4: New USB device found, 
idVendor=091e, idProduct=28db, bcdDevice= 5.09||
||janv. 23 23:01:29 host kernel: usb 2-4: New USB device strings: Mfr=0, 
Product=0, SerialNumber=5||
||...||
||# GPS in preboot mode||
||...||
||janv. 23 23:09:05 host kernel: usb 2-4: New USB device found, 
idVendor=091e, idProduct=0003, bcdDevice= 0.01||
||janv. 23 23:09:05 host kernel: usb 2-4: New USB device strings: Mfr=0, 
Product=0, SerialNumber=0||
||janv. 23 23:09:13 host kernel: garmin_gps ttyUSB0: Garmin GPS usb/tty 
converter now disconnected from ttyUSB0|
...

We see that *idVendor*, *idProduct*, *bcdDevice*, *Mfr*, *Product* and 
*SerialNumber* vary according to the modes.We also see that the GPS is 
seen as a *ttyUSB0* serial device.

I managed to attach the GPS in preboot mode, thanks to a script which 
waits for the GPS to be detected in this mode (not detailed here so as 
not to overload, but I can publish it if necessary) and which attaches 
to a VM in running (*successfully tested on Debian 11 **and**Windows 7 
guests*).

Here is the code that generates the XML before attaching it :

|...||
||echo    "<serial type='dev'> \||
||            <source path='"$( \||
||             ls -1 /dev/tty* | grep -Ev "tty(|S?[0-9]+)$" \||
||            )"'/> \||
||            <target type='usb-serial'> \||
||                <vendor id='0x"$( \||
||                 echo 091e \||
||                )"'/> \||
||                <product id='0x"$( \||
||                 echo 28db \||
||                )"'/> \||
||            </target> \||
||        </serial>" > serial_device.xml||
||virsh attach-device vm-bullseye --file serial_device.xml &||
||...|

But once attached, this is what I see in the XML configuration of my VM 
(from *virt-manager*) :

|<serial type="dev">||
||  <source path="/dev/ttyUSB1"/>||
||  <target type="usb-serial" port="1">||
||    <model name="usb-serial"/>||
||  </target>||
||  <alias name="serial1"/>||
||  <address type="usb" bus="0" port="4"/>||
||</serial>|

We see that libvirt has removed the *vendor/product id* from the XML.

Also here is what I get from a *Debian 11 guest* :

|root at vm-bullseye:~# journalctl -k -f||
||...||
||janv. 23 21:26:22 vm-bullseye kernel: usb 3-2: new full-speed USB 
device number 2 using uhci_hcd||
||janv. 23 21:26:22 vm-bullseye kernel: usb 3-2: New USB device found, 
idVendor=0403, idProduct=6001, bcdDevice= 4.00||
||janv. 23 21:26:22 vm-bullseye kernel: usb 3-2: New USB device strings: 
Mfr=1, Product=2, SerialNumber=4||
||janv. 23 21:26:22 vm-bullseye kernel: usb 3-2: Product: QEMU USB SERIAL||
||janv. 23 21:26:22 vm-bullseye kernel: usb 3-2: Manufacturer: QEMU||
||janv. 23 21:26:22 vm-bullseye kernel: usb 3-2: SerialNumber: 
1-0000:00:05.7-4||
||janv. 23 21:26:22 vm-bullseye kernel: usbcore: registered new 
interface driver usbserial_generic||
||janv. 23 21:26:22 vm-bullseye kernel: usbserial: USB Serial support 
registered for generic||
||janv. 23 21:26:22 vm-bullseye kernel: usbcore: registered new 
interface driver ftdi_sio||
||janv. 23 21:26:22 vm-bullseye kernel: usbserial: USB Serial support 
registered for FTDI USB Serial Device||
||janv. 23 21:26:22 vm-bullseye kernel: ftdi_sio 3-2:1.0: FTDI USB 
Serial Device converter detected||
||janv. 23 21:26:22 vm-bullseye kernel: usb 3-2: Detected FT232BM||
||janv. 23 21:26:22 vm-bullseye kernel: usb 3-2: FTDI USB Serial Device 
converter now attached to ttyUSB0||
||janv. 23 21:26:25 vm-bullseye kernel: usb 3-2: USB disconnect, device 
number 2||
||janv. 23 21:26:25 vm-bullseye kernel: ftdi_sio ttyUSB0: FTDI USB 
Serial Device converter now disconnected from ttyUSB0||
||janv. 23 21:26:25 vm-bullseye kernel: ftdi_sio 3-2:1.0: device 
disconnected||
||...|

The guest sees the GPS well but
idVendor=*0403*, idProduct=*6001*, bcdDevice=4.00, Mfr=1, Product=2, 
SerialNumber=4
... do not correspond to anything, and tools that expect GPS in preboot 
mode do not see it.


My questions :

Q1 : Is it possible ?

Q2 : Am I doing it the right way ?

Q3 : Is there a method to pass such a device directly (pass-through) ?


Thank you in advance for the time you are going to devote to me :)

With Adelphity,

lnj
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