On 29/11/2016 10:39, Pantelis Antoniou wrote: > 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. The fact that they can doesn't mean they necessarily should. > >> 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 :) Not really, no. With the current scheme we have control over the scope, but now there is none. How does your patch handle duplicate symbols? Phil -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
