linux-kernel - Re: [PATCH] USB: serial: option: adding support for ublox R410M

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Date:   Wed, 2 May 2018 09:22:16 +0200
From:   Johan Hovold <johan@...nel.org>
To:     Dan Williams <dcbw@...hat.com>
Cc:     Johan Hovold <johan@...nel.org>, Lars Melin <larsm17@...il.com>,
        Bjørn Mork <bjorn@...k.no>,
        SZ Lin (林上智) <sz.lin@...a.com>,
        stable <stable@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] USB: serial: option: adding support for ublox R410M

On Thu, Apr 26, 2018 at 02:12:32PM -0500, Dan Williams wrote:
> On Thu, 2018-04-26 at 18:29 +0200, Johan Hovold wrote:
> > On Thu, Apr 26, 2018 at 11:22:25PM +0700, Lars Melin wrote:
> > > On 4/26/2018 23:12, Johan Hovold wrote:
> > > > On Thu, Apr 26, 2018 at 06:40:46PM +0700, Lars Melin wrote:
> > > > > On 4/26/2018 18:39, Lars Melin wrote:
> > > > > > On 4/26/2018 18:19, Bjørn Mork wrote:
> > > > > > > Anyway, Qualcomm based designs are definitely handled by
> > > > > > > both drivers.  Using qcserial only makes sense if the
> > > > > > > interface layout matches one of the defined shared
> > > > > > > schemes, which currently are:
> > > > > > > 
> > > > > > >      QCSERIAL_G2K = 0,    /* Gobi 2000 */
> > > > > > >      QCSERIAL_G1K = 1,    /* Gobi 1000 */
> > > > > > >      QCSERIAL_SWI = 2,    /* Sierra Wireless */
> > > > > > >      QCSERIAL_HWI = 3,    /* Huawei */
> > > > > > 
> > > > > > It seems to me that this Quectel device matches the
> > > > > > interface layout for Gobi1K:
> > > >
> > > > Yeah, but qcserial appears to select a different altsetting for
> > > > the DM port for Gobi 1000, an altsetting which this particular
> > > > device does not have.
> > > > 
> > > > I didn't re-read the full thread I referred to earlier, but I
> > > > think in it, Dan mentioned Gobi 1000 device requiring firmware
> > > > to be loaded too.
> > > > 
> > > > So if it's not a G1K device, we probably shouldn't be using
> > > > qcserial even if the interface layout happens to match.
> > >
> > > Good point, I forgot about the required firmware loading for
> > > Gobi1K.
> > > So this device should be handled by the option driver.
> > 
> > Yeah, we probably should document all of this at some point. :)
> > 
> > I didn't include the patch in this weeks -rc updates, but I've
> > queued it up for the next batch.
> 
> Option is likely the right driver for this device.
> 
> qcaux was mainly for mobile phones that have a TTY (often cdc-acm) as
> the modem port and a secondary DIAG/DM port driven by qcaux.  The DM
> port doesn't have an interrupt endpoint thus it's not a normal modem
> port requiring the larger buffers of option and its control signaling.
> 
> qcserial (as Bjorn mentioned) is only for actual Gobi-type devices with
> the specific layouts and the firmware loading requirement where the 1K
> and 2K devices start in a special 1-port mode waiting for firmware and
> then become 4-port devices on firmware reboot.

Thanks for that summary. I've applied SZ's patch now.

Johan