From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Gibson Subject: Re: [PATCH 6/6] OF: Introduce DT overlay support. Date: Wed, 23 Jan 2013 16:12:07 +1100 Message-ID: <20130123051207.GA2228@truffula.fritz.box> References: <1357327870-13615-1-git-send-email-panto@antoniou-consulting.com> <1357327870-13615-7-git-send-email-panto@antoniou-consulting.com> <20130122035056.GF23500@truffula.fritz.box> <9768253B-92ED-4298-8BE4-6FAB091DF062@antoniou-consulting.com> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="X1bOJ3K7DJ5YkBrT" Return-path: Content-Disposition: inline In-Reply-To: <9768253B-92ED-4298-8BE4-6FAB091DF062@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 --X1bOJ3K7DJ5YkBrT Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Tue, Jan 22, 2013 at 01:08:04PM +0200, Pantelis Antoniou wrote: > Hi >=20 > On Jan 22, 2013, at 5:50 AM, David Gibson wrote: >=20 > > 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/Documentatio= n/devicetree/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 an= d is 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. > >=20 > > Um.. I'm having a great deal of trouble parsing that sentence. > >=20 > >> +Since the kernel mainly deals with devices, any new device node that = result > >> +in an active device should have it created while if the device node i= s either > >> +disabled or removed all together, the affected device should be dereg= istered. > >> + > >> +Lets take an example where we have a foo board with the following bas= e tree > >> +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]) s= hould > >> + > >> +---- 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 crea= ted > >> +so a bar platform device will be registered and if a matching device = driver > >> +is loaded the device will be created as expected. > >=20 > > Hrm. This all seems rather complicated. Maybe it needs to be, but > > I'm not entirely convinced yet. > >=20 > > 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 > Sorry, I can't parse this. You mean apply the overlay without converting > to live tree format? Yes. --=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 --X1bOJ3K7DJ5YkBrT Content-Type: application/pgp-signature; name="signature.asc" Content-Description: Digital signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.12 (GNU/Linux) iEYEARECAAYFAlD/cScACgkQaILKxv3ab8bIgACfZlGpU9eJvXLEn8008K699nqi hdAAnj1mGidAyaP8a7bDt0RX++wM4Gvk =drKY -----END PGP SIGNATURE----- --X1bOJ3K7DJ5YkBrT--