Hi Phil, > On Nov 29, 2016, at 12:32 , Phil Elwell <phil@xxxxxxxxxxxxxxx> wrote: > > On 29/11/2016 02:11, David Gibson wrote: >> On Mon, Nov 28, 2016 at 12:24:20PM +0000, Phil Elwell wrote: >>> On 28/11/2016 12:10, Pantelis Antoniou wrote: >>>> For plugins we need the __symbols__ node to support stacked overlays, i.e. >>>> overlays referring label that were introduced by a previous overlay. >>> Although it is arguably useful to be able to refer to symbols created by >>> one overlay from within another, do we really want all symbols to be >>> global? Isn't there a call for a new syntax or usage pattern to indicate >>> either that a symbol should be local to the overlay or, my preferred >>> option, global? >> So, this is back to a design question about the overlay format. As >> noted in the initial discussions about possible "connector" formats, I >> think we will want some sort of local symbols. But the current >> overlay format with all global symbols is out there and we need to >> support it. > The overlay format we have does not dictate the scope of the symbols. > > In all implementations I know of - the Raspberry Pi loader, the current > Linux kernel, the latest dtc patch set - there is a completely > asymmetric relationship between the base DTB and an overlay: > * the base DTB exports __symbols__ to resolve the overlays unresolved > label references, as recorded by the __fixups__ node > * the overlay's phandles are renumbered so as not to clash with the base > tree using the __local_fixups__ > * the contents of the __overlay__ nodes are applied to the base tree, as > directed by the "target" or "target-path” properties > Yes > The __symbols__ node of the overlay is ignored and discarded. The > __fixups__ and __local_fixups__ in the base DTB (if present - the RPi > dtc only generates them for /plugins/) are ignored. > That was a limitation that no-longer applies. Overlay symbols can be added to the base tree symbol list with a small patch I have already posted. > In the set of RPi overlays only one exports a global symbol, which it > achieves with an overlay aimed at target-path = "/__symbols__" that adds > a new symbol (in this case "i2c_gpio"). > > If the __symbols__ in an overlay are automatically merged with the base > symbols, that is a significant change in semantics which needs to be > discussed. > You no longer need to do this anymore. Hope this helps :) > Phil Regards — Pantelis -- To unsubscribe from this list: send the line "unsubscribe devicetree-compiler" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
