Re: [PATCH 0/7] gnss: add new GNSS subsystem

From: Pavel Machek <pavel@ucw.cz>
To: Sebastian Reichel <sebastian.reichel@collabora.co.uk>
Cc: Johan Hovold <johan@kernel.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Rob Herring <robh+dt@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Andreas Kemnade <andreas@kemnade.info>,
	Arnd Bergmann <arnd@arndb.de>,
	"H . Nikolaus Schaller" <hns@goldelico.com>,
	linux-kernel@vger.kernel.org, devicetree@vger.kernel.org
Subject: Re: [PATCH 0/7] gnss: add new GNSS subsystem
Date: Sat, 5 May 2018 23:11:29 +0200	[thread overview]
Message-ID: <20180505211129.GA762@amd> (raw)
In-Reply-To: <20180505172847.qqpqkrfspak53sc6@earth.universe>

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Hi!

> > > (*) I have those in mind:
> > > 
> > > Nokia N900: The phone has GPS integrated into the modem and uses
> > > ISI encapsulated data. The protocol has been reverse engineered
> > > and it should be possible to write a kernel driver for handling
> > > the GPS packets and dumping the raw data to /dev/gnss0. I don't
> > > think this is particularly useful without a non-raw interface,
> > > though. It would still require a custom userspace implementation.
> > 
> > Actually... in this case it would be nice to do the protocol
> > processing in kernel and just present reasonable interface to
> > userland... or maybe NMEA.
> 
> Converting a binary protocol to NMEA, which needs to be string
> parsed is not very nice. I think first step would be to write a
> simple driver, which exposes the binary location protocol without
> ISI header. Then in a second step we can think about a reasonable
> interface, that should be supported by all GNSS devices.

Well, most of the userspace expects NMEA. So yes, its an ugly
protocol, but .. it is not really a high-performance device.

I'd suggest modeling this over input subsystem. We could use similar
tag/value/sync protocol (evdev). In similar way /dev/input/mice was
used for running legacy apps during transition, we'd have /dev/...//nmea.

> > > Droid 4: GPS is similar to N900, but different protocol and QMI
> > > encapsulated. This one also has known protocol with userspace
> > > implementation. I did not yet have a detailed look, if its possible
> > > to (un)wrap this in the kernel.
> > 
> > So, this is actually NMEA over QMI. I do have patches libqmi that
> > provides NMEA on stdout.
> 
> Ok. So raw data is NMEA for this one. Should be reasonably easy to
> write a driver exposing this via /dev/gnss device.

If we have qmi implementation somewhere in kernel. Do we?

> > But there seems to be another possibile interface (yes, that modem is
> > crazy, and you can talk to it over few different interfaces), and
> > that's NMEA over GSM07.10. That one should be feasible to decode in
> > kernel and just provide NMEA to userland.
> 
> I think both should be feasible. I suggest to wait a bit more
> until you and Tony figured out some more details. You've got
> the libqmi patch as workaround for now and we want a stable API
> later.

I do have the gsm07.10 one now, too. That one is certainly simple
enough (and should eat less power -- no need to keep USB running).

Best regards,
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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