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

[Russell King - ARM Linux]

On Wed, Apr 27, 2016 at 07:48:18AM -0500, Rob Herring wrote:
> On Wed, Apr 27, 2016 at 3:59 AM, Russell King - ARM Linux
> <linux at arm.linux.org.uk> wrote:
> > 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.
> 
> I'm not suggesting that we change behavior at all. I'm only suggesting
> that we leave it undefined in the binding documentation because the
> behavior is possibly OS specific and can't really be defined there.

Ok.

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