linux-kernel - Re: [RFC PATCH 0/3] bluetooth/gnss: GNSS support for TiWi chips

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Date:   Fri, 8 Dec 2023 18:47:53 +0100
From:   Andreas Kemnade <andreas@...nade.info>
To:     Adam Ford <aford173@...il.com>
Cc:     Tony Lindgren <tony@...mide.com>, marcel@...tmann.org,
        johan.hedberg@...il.com, luiz.dentz@...il.com, johan@...nel.org,
        arnd@...db.de, gregkh@...uxfoundation.org,
        linux-bluetooth@...r.kernel.org, linux-kernel@...r.kernel.org,
        tomi.valkeinen@...asonboard.com,
        Péter Ujfalusi <peter.ujfalusi@...il.com>,
        robh@...nel.org
Subject: Re: [RFC PATCH 0/3] bluetooth/gnss: GNSS support for TiWi chips

Hi,

On Fri, 8 Dec 2023 08:39:21 -0600
Adam Ford <aford173@...il.com> wrote:

> On Mon, Nov 27, 2023 at 2:51 PM Andreas Kemnade <andreas@...nade.info> wrote:
> >
> > Hi,
> >
> > On Mon, 27 Nov 2023 15:54:24 +0200
> > Tony Lindgren <tony@...mide.com> wrote:
> >
> > [...]  
> > > > - Output at /dev/gnssX:
> > > >   AI2 vs. NMEA
> > > >   The chip can be configured into sending AI2-encapsulated NMEA,
> > > >   or proving data in a binary format.
> > > >   Some research has to be done yet for the details.
> > > >   A pile of logs is waiting for further analysis...
> > > >
> > > >   Arguments for/against NMEA:
> > > >   + Userspace is prepared to handle it
> > > >   + Power management can be easily done by the kernel
> > > >   - Less functionality can be used.  
> > >
> > > I'd go with NMEA format as the default setting :)
> > >  
> > yes, that would also be my preference.
> >  
> > > >   Arguments for/against AI2:
> > > >   + Full functionality can be accessed from userspace (incl. A-GPS,
> > > >     maybe raw satellite data)
> > > >   - Userspace has to behave to have proper power management
> > > >   - No freely (not even as in beer) tool available to fully use AI2,
> > > >     so there will be only a real advantage after long "French Cafe"
> > > >     sessions.  
> > >
> > > Seems AI2 could be optionally enabled as needed with some writes
> > > to /dev/gnss0 to change the mode?  
> >
> > Hmm, we have
> > /sys/class/gnss/gnss0/type to get the mode, maybe we add some file
> > to change the mode? Or having it hidden behing a module parameter
> > and implement something better accessible if any need arrives?
> >
> > If we want NMEA output, probably some init commands will be sent at
> > open(), but userspace doing something with AI2 probably does not want
> > the device touched, so it should probably be already be set before open().  
> 
> Is there another revision coming or should I try to test this one?  I
> am not very familiar with the GNSS part of the module, but it sounds
> like there was some consensus as to which direction we should go.  I
> should have a little time this weekend.
> 
Progress is only in my test program. No more checksum errors, I have
made some progress in protocol reverse engineering. So make sure
you do a git pull for https://github.com/akemnade/bt200tools

Regards,
Andreas