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

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Date:   Tue, 8 May 2018 09:01:53 +0200
From:   Johan Hovold <johan@...nel.org>
To:     Marcel Holtmann <marcel@...tmann.org>
Cc:     Johan Hovold <johan@...nel.org>,
        Sebastian Reichel <sebastian.reichel@...labora.co.uk>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Andreas Kemnade <andreas@...nade.info>,
        Arnd Bergmann <arnd@...db.de>,
        "H . Nikolaus Schaller" <hns@...delico.com>,
        Pavel Machek <pavel@....cz>,
        LKML <linux-kernel@...r.kernel.org>, devicetree@...r.kernel.org
Subject: Re: [PATCH 0/7] gnss: add new GNSS subsystem

On Mon, May 07, 2018 at 09:06:44PM +0200, Marcel Holtmann wrote:

> >> I have one concern, though. While providing raw data by
> >> default is fine generally, it is a problem with device
> >> auto-discovery. I think there should be some IOCTL from
> >> the start, that can be used to inform userspace about
> >> the raw protocol being used (i.e. "NMEA"). I fear, that
> >> userspace may start to just assume raw = NMEA without
> >> having this (especially since all initial drivers provide
> >> NMEA).
> > 
> > One problem I see here would be that the driver does not necessarily
> > know either what protocol is currently being used. Some devices have
> > boot-pins which can be used to configure the initial protocol used (and
> > this could perhaps be reflected in DT), but this can often later be
> > changed (by user space) and even be made persistent using battery-backed
> > ram or eeproms.
> > 
> > Also note that at least u-blox devices supports having more than one
> > protocol active on the same port...
> 
> as long as userspace can determine that it is GNSS hardware and what
> hardware it is, then you deal with the rest in userspace.

Yeah, I think that will do for now.

Thanks,
Johan