E173s-1 stops working after weeks of uptime

Ladislav Michl ladis at linux-mips.org
Fri May 31 09:18:15 UTC 2019

On Thu, May 30, 2019 at 09:46:01PM -0500, Dan Williams wrote:
> On Fri, 2019-05-31 at 00:01 +0200, Ladislav Michl wrote:
...and I'll eventually create new thread to not continue hikacking this one.
> > I'm using MM&NM restart and if that doesn't help, then modem
> > powercycle and
> > then daemon restart. Boards do have modem power supply controlled by
> > gpio,
> > so that's easy to do, but rather hackish. Is there any plan to add
> > some
> > "modem hw reset" infrastructure here?
> We've thought about it before, but the problem is that it's pretty
> unreliable for USB ports on most machines that aren't embedded.
> Basically, you cannot guarantee that the USB host controller supports
> the command to power cycle a port, and a lot of them just don't.
> You can't expect the USB port reset to work, because that's a USB
> request to the firmware running on the device IIRC and if the device is
> already hung it's surely not going to pay attention to a reset request.

Even worse, many quectels have nRST and PWR_KEY pins which name suggests
to reset or power down/up them, but those are just gpios for them, so the
only reliable way to reset is power cycle. And most of sane hardware
designers are creating their hardware with that in mind.

> So basically yes, that infrastructure could be added, but there's no
> way you can depend on the request actually succeeding especially on x86
> machines.

I'm not talking about making it anyhow mandatory and not even about
ordinary laptops or PCs with frustrated user always able to replug poor
USB modem once their favourite web page stops loading.

ModemManager hit OpenWrt recently and is in PTXdist for ages, so number
of "embedded" instalations could easily overgrow those "ordinary" ones.
And each that embedded device have to deal with unreliable modem somehow,
so I'd say it could be usefull to have at least some recomendation
how to handle such powercycles.

The thing is that those devices often do not have enough storage to run
MM with debug log level, are otherwise unreachable, their CPU is often
less powerfull than those used in modems (which could teoretically run
all that software running on the board they are plugged into, but that's
different story) and hangs does not occur so often, to be reasonably
debuggable. All that makes modem device power cycling the only reliable
way to recover in field (except whole machine power on reset, of course)


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