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 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. 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. 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
