More information on HP modem 03f0:521d

[Christian Ehrhardt]

Hi,

I have a HP Laptop with a HP branded UMTS modem HS3110 with ID
03f0:521d.  I've seen the people in the CC list in two discussions
about linux support for this modem.

I have this modem working in MBIM/NCM mode with a modified umb(4) driver
in OpenBSD (at least it pings) and I'd like share my findings. I haven't
tested linux but based on the current cdc_ncm code and my findings
the device probably does not work with linux and MBIM today.

So here we go:
- The device supports MBIM in configuration 2.
- The device does _not_ need the NTB_TO_END quirk (it doesn't hurt either).
- The device defaults to NTB32 format.
- The device reports that it supports both NTB16 and NTB32 formats.
- Trying to force the device to NTB16 mode allows one to send
  packets. However, the device does not work properly with NTB16 for
  the receive path.
- If the device is forced to use NTB16 format, all NCM related headers
  are missing in received data. The space is there but all fields
  are zeroed.
- One of the first "network" packets received from the modem is not
  really an IP packet. It contains the string "CONNECT 21600000"
  which according to google is a valid response to an AT command.
  However, if the packet is simply ignored (dropped as corrupt by the
  IP stack) things seem to work.

The only working option is apparently to use NTB32 format which
AFAICS is not yet possible with the linux-kernel MBIM drivers.

     regards   Christian