Date: Fri, 12 Jan 2018 15:46:47 +0100
From: Johan Hovold <johan@kernel.org>
To: Andreas Kemnade <andreas@kemnade.info>
Cc: Johan Hovold <johan@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        devicetree@vger.kernel.org,
        Discussions about the Letux Kernel 
        <letux-kernel@openphoenux.org>,
        Jonathan Cameron <jic23@kernel.org>,
        Arnd Bergmann <arnd@arndb.de>,
        Tony Lindgren <tony@atomide.com>,
        "H. Nikolaus Schaller" <hns@goldelico.com>,
        kernel@pyra-handheld.com, Russell King <linux@armlinux.org.uk>,
        linux-kernel@vger.kernel.org, Thierry Reding <treding@nvidia.com>,
        Rob Herring <robh+dt@kernel.org>,
        Kevin Hilman <khilman@baylibre.com>,
        =?iso-8859-1?Q?Beno=EEt?= Cousson <bcousson@baylibre.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-omap@vger.kernel.org,
        Andreas =?iso-8859-1?Q?F=E4rber?= <afaerber@suse.de>,
        linux-arm-kernel@lists.infradead.org
Subject: Re: [Letux-kernel] [PATCH v5 3/5] misc serdev: Add w2sg0004 (gps
 receiver) power control driver
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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@kernel.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