[PATCH v2 2/2] Documentation: devicetree: Add PL310 PM bindings

[Russell King - ARM Linux]

On Wed, Apr 20, 2016 at 09:04:39AM -0500, Rob Herring wrote:
> On Tue, Apr 19, 2016 at 5:41 PM, Russell King - ARM Linux
> <linux at arm.linux.org.uk> wrote:
> > On Tue, Apr 19, 2016 at 04:38:14PM -0500, Rob Herring wrote:
> >> On Mon, Apr 18, 2016 at 4:36 PM, Brad Mouring <brad.mouring at ni.com> wrote:
> >> > Document the DT bindings for controlling ARM PL310 Power Control
> >> > settings.
> >> >
> >> > Signed-off-by: Brad Mouring <brad.mouring at ni.com>
> >>
> >> What happened to Josh's ack?
> >>
> >> > ---
> >> >  Documentation/devicetree/bindings/arm/l2c2x0.txt | 4 ++++
> >> >  1 file changed, 4 insertions(+)
> >> >
> >> > diff --git a/Documentation/devicetree/bindings/arm/l2c2x0.txt b/Documentation/devicetree/bindings/arm/l2c2x0.txt
> >> > index fe0398c..c1c756e 100644
> >> > --- a/Documentation/devicetree/bindings/arm/l2c2x0.txt
> >> > +++ b/Documentation/devicetree/bindings/arm/l2c2x0.txt
> >> > @@ -84,6 +84,10 @@ Optional properties:
> >> >  - prefetch-instr : Instruction prefetch. Value: <0> (forcibly disable),
> >> >    <1> (forcibly enable), property absent (retain settings set by
> >> >    firmware)
> >> > +- arm,dynamic-clock-gating : L2 dynamic clock gating. Value: <0> (forcibly
> >> > +  disable), <1> or property absent (forcibly enable)
> >> > +- arm,standby-mode: L2 standby mode enable. Value <0> (forcibly disable),
> >> > +  <1>  or property absent (forcibly enable)
> >>
> >> What happened to "retain settings set by firmware"?
> >
> > I said we shouldn't.  Current behaviour is that we enable these features,
> > and moving to missing-means-retain means that everything today ends up
> > with these features disabled.  IOW, it's yet another change of actual
> > behaviour that every platform would see.
> 
> Right, but then the properties are different from prefetch-instr and
> others IIRC. We're letting the OS define the binding. If BSD doesn't
> enable these settings currently, then there is a mismatch between the
> binding and actual behavior. Saying "retain firmware settings" also
> defines specific OS behavior. I think absent should mean OS is free to
> do whatever it wants which could be retain firmware settings, enable
> or disable. In other words, it is undefined as this ship has already
> sailed.

I agree with "the ship has already sailed" but I disagree with the
rest of your comment.  The ship has already sailed in that we have
an established behaviour which has been there for 18 months.  Given
the time period, it's not something I'm going to change at this
stage, sorry.

Why?  Such a change will go unnoticed, and it's particularly hard
to debug why battery life has reduced.

I guess we need to find a way to ensure that the default behaviour
stays.  Whether that's by _everyone_ updating their DT files with
the new properties or some other way, I don't care.  I only care
that we retain the behaviour we've had for the last 18 months.

-- 
RMK's Patch system: http://www.arm.linux.org.uk/developer/patches/
FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up
according to speedtest.net.