usb_modem and mbimcli

[Christian Helmuth]

Hello Pirmin,

we had an offline brainstorming in the Genode Labs team about the
issue you raised. Unfortunately, we could not come up with a concrete
suggestion how you could tackle the timeout. It seems timeouts happen
sporadically during communication with the SIM card depending on the
platform and modem device used. This hints that Linux tools may also
face such issues and it may be worth to investigate the behavior when
controlling the modem on a Linux host. Building and instrumenting the
mbimcli tool for Linux should not be too hard.

On Mon, Oct 25, 2021 at 15:37:35 CEST, Duss Pirmin wrote:
> In rare cases the following message also appears in the output:
> ```
> [init -> usb_modem_drv] dev_err: nonzero urb status received: -EPIPE
> ```
> I'm not sure if it is related, but as the modem is connected via USB it
> could be.
> 
> The device is connected to a iMX8m mini, which uses the same
> `usb_host_drv` as the iMX6q sabrelite.

The message comes from cdc-wdm.c that also includes the following
comment, which hints a temporary (?) USB stall.

   * Avoid propagating -EPIPE (stall) to userspace since it is
   * better handled as an empty read

Regards
-- 
Christian Helmuth
Genode Labs

https://www.genode-labs.com/ · https://genode.org/
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