From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Gibson Subject: Re: [PATCH v10 3/4] dtc: Plugin and fixup support Date: Wed, 30 Nov 2016 12:41:34 +1100 Message-ID: <20161130014134.GD19891@umbus> 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: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="eqp4TxRxnD4KrmFZ" Return-path: Content-Disposition: inline In-Reply-To: Sender: devicetree-compiler-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Phil Elwell 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 --eqp4TxRxnD4KrmFZ Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Tue, Nov 29, 2016 at 10:32:28AM +0000, Phil Elwell 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 indica= te > >> 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. >=20 > 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 >=20 > 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. >=20 > In the set of RPi overlays only one exports a global symbol, which it > achieves with an overlay aimed at target-path =3D "/__symbols__" that adds > a new symbol (in this case "i2c_gpio"). >=20 > 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. Symbols are global, they really can't be anything else in this format. This is why I think the connector approach - though substantially more complex - is a better idea in the wrong run. --=20 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 --eqp4TxRxnD4KrmFZ Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v2 iQIcBAEBCAAGBQJYPi5LAAoJEGw4ysog2bOSLQsQAMUSE34j1iNVi71MCTYmRR7f gtlPgdmRouzylTp6yVOkMJSjlXq4kbvMKqkCCtUcXJnl33QIWIST4/bBmxo6iids fvgGiFK9VEMB4hu0WFcKCqXtQ0niDZnRCXjjkvGh+2pFtDl3Jt5ViLrFmf+rPU4s Kwc9+oSd2vzW2Anh8BYG/WJaRLOG/rqY16h3y7JPmQfWIO3GoYq4OE2ydrXX7x/D qn1EjtWqIbC9nvJri0dkfO6302FbcnM8HdH46MTQSlf+kjY5ias1N9DHiJWdoOgf hbIXFDtRIOPM55eorYMSiS8uOquvYwXFemk95tBAZm/tlx1ypf/N06ORLCspUyxO ibGCwoyPFBE2ksdWe/rncXZCjZuoCjq0s613U/OawGdb5rhG5zdmUQPNOvKUiKKv JRWiexLe11IYiNdh9nv9eLVHpZ7PX96YgN1lhnaPrpYt9fMbDYENnCshJx5xJsmc i7JbsbpTWxFBmIg0P5y6ppr8bJEkn2fGKDSpy2k85LANLxUFMpvlvE1K8ndy1l0A FVyPkJRJkrH+Y9oddoJw6A8UnWxVw6I7nmbqybpK/lWCN2lhYi7ov2oOCucS2RnC ePigUFoOh4gj6kwq1Ibg18Zq7+kGHZlab4B0g9o8rGQu+Ieh1WKmM9PASqy4sLqk ThLRi7Plz79sZI33rutR =TwHu -----END PGP SIGNATURE----- --eqp4TxRxnD4KrmFZ--