From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Gibson Subject: Re: [PATCH 6/6] OF: Introduce DT overlay support. Date: Tue, 22 Jan 2013 14:50:56 +1100 Message-ID: <20130122035056.GF23500@truffula.fritz.box> References: <1357327870-13615-1-git-send-email-panto@antoniou-consulting.com> <1357327870-13615-7-git-send-email-panto@antoniou-consulting.com> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="Pql/uPZNXIm1JCle" Return-path: Content-Disposition: inline In-Reply-To: <1357327870-13615-7-git-send-email-panto@antoniou-consulting.com> Sender: linux-doc-owner@vger.kernel.org To: Pantelis Antoniou Cc: Grant Likely , Rob Herring , Rob Landley , Jon Loeliger , Tony Lindgren , Stephen Warren , Benoit Cousson , Mitch Bradley , Alan Tull , linux-omap@vger.kernel.org, devicetree-discuss@lists.ozlabs.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, Matt Porter , Russ Dill , Koen Kooi , Joel A Fernandes , Rob Clark , Jason Kridner , Matt Ranostay List-Id: devicetree@vger.kernel.org --Pql/uPZNXIm1JCle Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Fri, Jan 04, 2013 at 09:31:10PM +0200, Pantelis Antoniou wrote: > Introduce DT overlay support. > Using this functionality it is possible to dynamically overlay a part of > the kernel's tree with another tree that's been dynamically loaded. > It is also possible to remove node and properties. >=20 > Signed-off-by: Pantelis Antoniou > --- > Documentation/devicetree/overlay-notes.txt | 179 +++++++ > drivers/of/Kconfig | 10 + > drivers/of/Makefile | 1 + > drivers/of/overlay.c | 831 +++++++++++++++++++++++= ++++++ > include/linux/of.h | 107 ++++ > 5 files changed, 1128 insertions(+) > create mode 100644 Documentation/devicetree/overlay-notes.txt > create mode 100644 drivers/of/overlay.c >=20 > diff --git a/Documentation/devicetree/overlay-notes.txt b/Documentation/d= evicetree/overlay-notes.txt > new file mode 100644 > index 0000000..5289cbb > --- /dev/null > +++ b/Documentation/devicetree/overlay-notes.txt > @@ -0,0 +1,179 @@ > +Device Tree Overlay Notes > +------------------------- > + > +This document describes the implementation of the in-kernel > +device tree overlay functionality residing in drivers/of/overlay.c and i= s a > +companion document to Documentation/devicetree/dt-object-internal.txt[1]= & > +Documentation/devicetree/dynamic-resolution-notes.txt[2] > + > +How overlays work > +----------------- > + > +A Device Tree's overlay purpose is to modify the kernel's live tree, and > +have the modification affecting the state of the the kernel in a way that > +is reflecting the changes. Um.. I'm having a great deal of trouble parsing that sentence. > +Since the kernel mainly deals with devices, any new device node that res= ult > +in an active device should have it created while if the device node is e= ither > +disabled or removed all together, the affected device should be deregist= ered. > + > +Lets take an example where we have a foo board with the following base t= ree > +which is taken from [1]. > + > +---- foo.dts -----------------------------------------------------------= ------ > + /* FOO platform */ > + / { > + compatible =3D "corp,foo"; > + > + /* shared resources */ > + res: res { > + }; > + > + /* On chip peripherals */ > + ocp: ocp { > + /* peripherals that are always instantiated */ > + peripheral1 { ... }; > + } > + }; > +---- foo.dts -----------------------------------------------------------= ------ > + > +The overlay bar.dts, when loaded (and resolved as described in [2]) shou= ld > + > +---- bar.dts -----------------------------------------------------------= ------ > +/plugin/; /* allow undefined label references and record them */ > +/ { > + .... /* various properties for loader use; i.e. part id etc. */ > + fragment@0 { > + target =3D <&ocp>; > + __overlay__ { > + /* bar peripheral */ > + bar { > + compatible =3D "corp,bar"; > + ... /* various properties and child nodes */ > + } > + }; > + }; > +}; > +---- bar.dts -----------------------------------------------------------= ------ > + > +result in foo+bar.dts > + > +---- foo+bar.dts -------------------------------------------------------= ------ > + /* FOO platform + bar peripheral */ > + / { > + compatible =3D "corp,foo"; > + > + /* shared resources */ > + res: res { > + }; > + > + /* On chip peripherals */ > + ocp: ocp { > + /* peripherals that are always instantiated */ > + peripheral1 { ... }; > + > + /* bar peripheral */ > + bar { > + compatible =3D "corp,bar"; > + ... /* various properties and child nodes */ > + } > + } > + }; > +---- foo+bar.dts -------------------------------------------------------= ------ > + > +As a result of the the overlay, a new device node (bar) has been created > +so a bar platform device will be registered and if a matching device dri= ver > +is loaded the device will be created as expected. Hrm. This all seems rather complicated. Maybe it needs to be, but I'm not entirely convinced yet. One other point - both of these patches are assuming that the overlay is in the "live tree" format, but it still needs a bunch of extra mangling. Would it simplify things to just go straight from the overlay in flat tree form to modifications to the system-wide live tree. --=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 --Pql/uPZNXIm1JCle Content-Type: application/pgp-signature; name="signature.asc" Content-Description: Digital signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.12 (GNU/Linux) iEYEARECAAYFAlD+DKAACgkQaILKxv3ab8a1bQCdHVwRPPq/XIGHB/7PsWQMfIBe vBMAnRkWwnob5D1uEZBG3Htmb3QCj9/R =uHL2 -----END PGP SIGNATURE----- --Pql/uPZNXIm1JCle--