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Date:   Mon, 7 May 2018 08:45:15 -0700
From:   Tony Lindgren <tony@atomide.com>
To:     Johan Hovold <johan@kernel.org>
Cc:     Sebastian Reichel <sre@kernel.org>,
        "H. Nikolaus Schaller" <hns@goldelico.com>,
        Andreas Kemnade <andreas@kemnade.info>,
        Mark Rutland <mark.rutland@arm.com>,
        Arnd Bergmann <arnd@arndb.de>, Pavel Machek <pavel@ucw.cz>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@vger.kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Rob Herring <robh+dt@kernel.org>
Subject: Re: [PATCH 4/7] dt-bindings: gnss: add u-blox binding
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Hi,

* Johan Hovold <johan@kernel.org> [180507 03:03]:
> On Fri, May 04, 2018 at 01:42:13PM +0200, Sebastian Reichel wrote:
> 
> > Having said all of this, serdev does not yet support runtime PM (at
> > all). Tony is currently looking into it. Fortunately serdev allows
> > us to enable runtime PM by default (once implemented), since we know
> > the remote side and can (hopefully) avoid losing characters (i.e.
> > with sideband wakeup gpios).
> 
> I'm not sure we want generic runtime-pm support for the controllers in
> the sense that the slave device state is always reflected by the serial
> controller. Similar as for i2c and spi, we really only want to keep the
> controller active when we are doing I/O, but we may want to keep a
> client active for longer.

Yeah i2c seems to do the right thing where the bus takes care
of runtime PM.

> Take the u-blox driver in this series for example. As I'm using runtime
> PM to manage device power, user-space can chose to prevent the receiver
> from runtime suspending in order to avoid lengthy (re-)acquisition times
> in setups without a backup battery (by means of the power/control
> attribute).

Sorry I don't seem to have that one, care to paste the subject
line of that patch?

> Note that serdev not enabling runtime pm for controllers is roughly
> equivalent to setting the .ignore_children flag, which is what we do for
> i2c and spi controller, and possibly what we want here too.

We currently don't idle serdev at all even if not in use. What
I noticed is if I have these in my .config:

CONFIG_SERIAL_DEV_BUS=y
CONFIG_SERIAL_DEV_CTRL_TTYPORT=y

And no hci_serdev.ko driver loaded, then the 8250 port still stays
active and there are no sysfs entries to idle it.

Are you seeing this with your series?

Regards,

Tony