linux-kernel - Re: [Letux-kernel] [PATCH v5 3/5] misc serdev: Add w2sg0004 (gps receiver) power control driver

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Date:   Mon, 19 Mar 2018 14:54:18 +0100
From:   Johan Hovold <johan@...nel.org>
To:     "H. Nikolaus Schaller" <hns@...delico.com>
Cc:     Johan Hovold <johan@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        DTML <devicetree@...r.kernel.org>,
        Discussions about the Letux Kernel 
        <letux-kernel@...nphoenux.org>,
        Benoît Cousson <bcousson@...libre.com>,
        Arnd Bergmann <arnd@...db.de>,
        Tony Lindgren <tony@...mide.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        kernel@...a-handheld.com, Russell King <linux@...linux.org.uk>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-omap <linux-omap@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Pavel Machek <pavel@....cz>,
        Kevin Hilman <khilman@...libre.com>,
        Thierry Reding <treding@...dia.com>,
        Andreas Färber <afaerber@...e.de>,
        Jonathan Cameron <jic23@...nel.org>
Subject: Re: [Letux-kernel] [PATCH v5 3/5] misc serdev: Add w2sg0004 (gps
 receiver) power control driver

On Tue, Feb 27, 2018 at 08:32:50AM +0100, H. Nikolaus Schaller wrote:
> Hi Johan,
> 
> > Am 27.02.2018 um 08:04 schrieb Johan Hovold <johan@...nel.org>:
> > 
> > On Mon, Feb 12, 2018 at 04:26:18PM +0100, Pavel Machek wrote:
> >> Hi!
> >> 
> >>>> Let's restart this discussion and focus on the main roadblock (others
> >>>> are minor details which can be sorted out later).
> >>>> 
> >>>> If it feels like a hack, the key issue seems to me to be the choice of
> >>>> the API to present the GPS data to user space. Right?
> >>> 
> >>> Or even more fundamentally, does this belong in the kernel at all?
> >> 
> >> Yes, it does.
> 
> Thanks, Pavel for supporting our view.
> 
> > 
> > But not necessarily in its current form.
> 
> Is this a "yes after some code fixes"?

No, we need some kind of at least rudimentary gps framework even if we
allow for a raw (NMEA) interface for the time being (possibly
indefinitely).

> Pavel mentioned an example where such an evolutionary approach was taken.
> > 
> >>> Now, if we'd ever have a proper GPS framework that handled everything in
> >>> kernel space (i.e. no more gpsd) then we would be able to write kernel
> >>> drivers that also take care of PM. But perhaps that's unlikely to ever
> >>> be realised given the state of things (proprietary protocols, numerous
> >>> quirky implementations, etc).
> >> 
> >> That is what needs to happen.
> >> 
> >>> The kernel is probably not the place to be working around issues like
> >>> that, even if serdev at least allows for such hacks to be fairly
> >>> isolated in drivers (unlike some of the earlier proposals touching core
> >>> code).
> >> 
> >> Oh, kernel is indeed right place to provide hardware abstraction --
> >> and that includes bug workarounds.
> > 
> > Right, at least when such hacks can be confined to a driver and not be
> > spread all over the place.
> 
> It seems that you forgot that the driver we propose is not spread all over
> the place. It *is* confined to a single driver thanks to the serdev api.

I believe that's what I wrote above.

Johan