linux-kernel - Re: [PATCH v2] USB: serial: qcserial: Support for SDX55 based Sierra Wireless 5G modules

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Message-ID: <YN7OBzmcsidWIG0F@hovoldconsulting.com>
Date:   Fri, 2 Jul 2021 10:27:51 +0200
From:   Johan Hovold <johan@...nel.org>
To:     Stefan Brüns <stefan.bruens@...h-aachen.de>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        Daniele Palmas <dnlplm@...il.com>,
        Bjørn Mork <bjorn@...k.no>
Subject: Re: [PATCH v2] USB: serial: qcserial: Support for SDX55 based Sierra
 Wireless 5G modules

On Thu, Jul 01, 2021 at 06:41:26PM +0200, Stefan Brüns wrote:
> On Donnerstag, 24. Juni 2021 09:28:59 CEST Johan Hovold wrote:
> > [ +CC: Daniele and Bjørn ]
> > 
> > On Fri, Jun 11, 2021 at 03:58:41PM +0200, Stefan Brüns wrote:
> > > The devices exposes two different interface compositions:
> > > - QDL mode, single interface
> > > - MBIM mode, MBIM class compliant plus AT/DM(/ADB)
> > > 
> > > Current firmware versions (up to 01.07.19) do not expose an NMEA port.
> > 
> > We already have at least one SDX55 based modem (FN980) supported by the
> > option driver. Any particular reason why you chose to add it to qcserial
> > instead of option?
> > 
> Support for qualcomm based modems are spread over option and qcserial. All 
> other Sierra devices are supported by qcserial.

Ok, but we may still end up adding this one to option if matching on the
interface protocol works.

> > Note that the FN980 also needs the ZLP flag set in QDL (flashing) mode,
> > I'd assume this one needs it too.
> 
> It depends if you implement the Firehose protocol in accordance to the 
> specification or not. 80-NG319-1 (Firehose specification) explicitly states to 
> pad any XML command packet which is an exact multiple of 512 bytes with an 
> extra newline or other whitespace character.

Thanks for the details. If you're referring to the device-side
implementation it seems a bit fragile to not just set the ZLP flag since
apparently there are some non-standard implementations out there. But
sure, we can do that later if needed.

Johan

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