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From: Phil Blundell <pb@pbcl.net>
To: Paul Barker <paul@paulbarker.me.uk>
Date: Wed, 22 May 2013 11:14:14 +0100
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Subject: Re: [oe] [RFC] Layers, PRINC and bbappends
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On Wed, 2013-05-22 at 09:47 +0100, Paul Barker wrote:
> I've just sent a patch to the yocto@ list to fix this but it's brought
> up two things:
> 
> 1) In openembedded-core/meta/classes/image.bbclass SPLASH is set with
> '?='. I'm overriding this with '=' in
> meta-raspberrypi/conf/machine/raspberrypi.conf which means it can't be
> overridden further in local.conf. Is this worth changing to '??=' in
> image.bbclass, '?=' in the machine conf so that it can be overridden
> with '=' in local.conf? Is my understanding of the overrides correct
> here?

You can always override it from local.conf using a _forcevariable
override (which used to be named "_local", in fact, but that terminology
turned out to be a bit confusing), or a _MACHINE override of course.  So
I don't think there is any major problem here.  

But, that said, it probably is true that the semantics of ??= are less
surprising for users (since it isn't position-dependent in the way
that ?= is) which might make it a better choice for image.bbclass.

p.