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

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Message-ID: <20180112144647.GA5992@localhost>
Date:   Fri, 12 Jan 2018 15:46:47 +0100
From:   Johan Hovold <johan@...nel.org>
To:     Andreas Kemnade <andreas@...nade.info>
Cc:     Johan Hovold <johan@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        devicetree@...r.kernel.org,
        Discussions about the Letux Kernel 
        <letux-kernel@...nphoenux.org>,
        Jonathan Cameron <jic23@...nel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Tony Lindgren <tony@...mide.com>,
        "H. Nikolaus Schaller" <hns@...delico.com>,
        kernel@...a-handheld.com, Russell King <linux@...linux.org.uk>,
        linux-kernel@...r.kernel.org, Thierry Reding <treding@...dia.com>,
        Rob Herring <robh+dt@...nel.org>,
        Kevin Hilman <khilman@...libre.com>,
        Benoît Cousson <bcousson@...libre.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-omap@...r.kernel.org,
        Andreas Färber <afaerber@...e.de>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [Letux-kernel] [PATCH v5 3/5] misc serdev: Add w2sg0004 (gps
 receiver) power control driver

On Tue, Jan 09, 2018 at 06:43:47PM +0100, Andreas Kemnade wrote:
> On Fri, 22 Dec 2017 13:44:27 +0100
> Johan Hovold <johan@...nel.org> wrote:
> 
> [...]
> > I'd suggest reiterating the problem you're trying to solve and
> > enumerating the previously discussed potential solutions in order to
> > find a proper abstraction level for this (before getting lost in
> > implementation details).
> > 
> The main point here is in short words: Having a device powered on or off
> when the uart it is attached to, is used or not used anymore,
> so the already available userspace applications do not need to be changed.

So we'd end up with something in-between a kernel driver and a
user-space solution. What about devices that need to be (partially)
powered also when the port isn't open? A pure user-space solution would
be able to handle all variants.

> I digged out a bit around:
> alternative aproaches were:
> adding hooks to the uart/tty layer:
> https://marc.info/?l=linux-kernel&m=143333222014616&w=2
> https://marc.info/?l=devicetree&m=143130955414580&w=2

Thanks for the pointers, I remember those threads...

> I do not find it right now in my archive:
> adding a virtual gpio for dtr to the omap_serial driver.
> The driver behind the virtual io would then handle pm. One reason it was
> rejected was that the devicetree should only contain real hardware and
> not virtual stuff.

Oh, yeah, I think something like that made it in briefly before getting
reverted again.

I'll respond to Nikolaus mail as well.

Johan