On Thu, May 03, 2018 at 01:00:04PM -0700, Frank Rowand wrote: > On 05/02/18 19:20, David Gibson wrote: > > On Wed, May 02, 2018 at 10:19:58AM +0100, Phil Elwell wrote: > >> David et al., > >> > >> I've mentioned before the problem posed for overlays by boolean properties, i.e. > >> that a boolean property that is "true" in a base DTB cannot be made "false" by an > >> overlay because doing so requires that the property be deleted. A solution for this > >> problem would be to define a new FDT tag - FDT_DEL_PROP, say - that is used to encode > >> any /delete-property/ found in a node during overlay compilation. When the overlay is > >> applied, the named property would be deleted if present. > >> > >> A heuristic would be needed to decide whether this property should be encoded or just > >> acted on immediately - the use of the '-@' command line parameter would seem to fit the > >> bill. > >> > >> Although one might consider extending this mechanism to cover node deletion, in practice > >> I think this would be too problematic in terms of broken phandle references etc., and in > >> most cases 'status = "disabled"' achieves the same objective, so I'm not proposing this > >> be added. > >> > >> Is such a change something you would consider supporting, or do you have an alternative > >> preferred solution? > > > > I'd certainly consider it within the right context. > > > > The difficulty is that this obviously requires changing the things > > that accept the fdt to understand the new format. And if we're going > > to do that, there's a bunch of other things we should change as well. > > I've previously had a discussion with Frank Rowand about how we could > > do a much saner encoding of the fixups using new tags, rather than the > > currently rather ghastly encoding in special properties and nodes. > > > > So maybe add this as one feature to put in a hypothetical v32 (or > > whatever) fdt format. > > I like this idea. > > On the question of current users of FDT objects, I think the problem is limited to > only overlays, so users of base FDTs should not be impacted. That at least reduces > the amount of code that needs to be updated. True. Note that we can already represent this, by setting the last_compat_version in the header based on whether the new encodings features are actually used or not. -- David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ | _way_ _around_! http://www.ozlabs.org/~dgibson
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