From mboxrd@z Thu Jan 1 00:00:00 1970 From: Phil Elwell Subject: Re: [PATCH v10 3/4] dtc: Plugin and fixup support Date: Tue, 29 Nov 2016 10:32:28 +0000 Message-ID: References: <1480077131-14526-1-git-send-email-pantelis.antoniou@konsulko.com> <1480077131-14526-4-git-send-email-pantelis.antoniou@konsulko.com> <20161128041228.GJ30927@umbus.fritz.box> <4672e164-aae0-6306-fe70-146a1f930cf7@raspberrypi.org> <20161129021131.GD13307@umbus.fritz.box> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20161129021131.GD13307-K0bRW+63XPQe6aEkudXLsA@public.gmane.org> Sender: devicetree-compiler-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: David Gibson Cc: Pantelis Antoniou , Jon Loeliger , Grant Likely , Frank Rowand , Rob Herring , Jan Luebbe , Sascha Hauer , Simon Glass , Maxime Ripard , Thomas Petazzoni , Boris Brezillon , Antoine Tenart , Stephen Boyd , Devicetree Compiler , devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: devicetree@vger.kernel.org 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