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[2603:6081:7b01:cbda:8054:417e:d97b:7576]) by smtp.gmail.com with ESMTPSA id v15sm7035716qta.82.2021.08.29.07.46.47 (version=TLS1_2 cipher=ECDHE-ECDSA-CHACHA20-POLY1305 bits=256/256); Sun, 29 Aug 2021 07:46:48 -0700 (PDT) Date: Sun, 29 Aug 2021 10:46:46 -0400 From: Tom Rini To: Simon Glass Cc: Mark Kettenis , Bin Meng , U-Boot Mailing List , Heinrich Schuchardt , Sean Anderson Subject: Re: [PATCH] doc: Add documentation about devicetree usage Message-ID: <20210829144646.GD858@bill-the-cat> References: <20210828032348.4570-1-sjg@chromium.org> <5614245d41c45ae2@bloch.sibelius.xs4all.nl> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="W6sWy1GDZvBCAepP" Content-Disposition: inline In-Reply-To: X-Clacks-Overhead: GNU Terry Pratchett User-Agent: Mutt/1.9.4 (2018-02-28) X-BeenThere: u-boot@lists.denx.de X-Mailman-Version: 2.1.34 Precedence: list List-Id: U-Boot discussion List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: u-boot-bounces@lists.denx.de Sender: "U-Boot" X-Virus-Scanned: clamav-milter 0.103.2 at phobos.denx.de X-Virus-Status: Clean --W6sWy1GDZvBCAepP Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Sun, Aug 29, 2021 at 07:03:14AM -0600, Simon Glass wrote: > Hi Mark, >=20 > On Sun, 29 Aug 2021 at 02:19, Mark Kettenis wro= te: > > > > > From: Simon Glass > > > Date: Sat, 28 Aug 2021 20:07:27 -0600 > > > > > > Hi Bin, > > > > > > On Sat, 28 Aug 2021 at 19:29, Bin Meng wrote: > > > > > > > > Hi Simon, > > > > > > > > On Sun, Aug 29, 2021 at 12:45 AM Simon Glass wro= te: > > > > > > > > > > Hi Bin, > > > > > > > > > > On Sat, 28 Aug 2021 at 07:15, Bin Meng wrote: > > > > > > > > > > > > Hi Simon, > > > > > > > > > > > > On Sat, Aug 28, 2021 at 11:23 AM Simon Glass = wrote: > > > > > > > > > > > > > > At present some of the ideas and techniques behind devicetree= in U-Boot > > > > > > > are assumed, implied or unsaid. Add some documentation to cov= er how > > > > > > > devicetree is build, how it can be modified and the rules abo= ut using > > > > > > > the various CONFIG_OF_... options. > > > > > > > > > > > > > > Signed-off-by: Simon Glass > > > > > > > --- > > > > > > > > > > > > > > doc/develop/index.rst | 1 + > > > > > > > doc/develop/package/devicetree.rst | 315 +++++++++++++++++++= ++++++++++ > > > > > > > doc/develop/package/index.rst | 1 + > > > > > > > 3 files changed, 317 insertions(+) > > > > > > > create mode 100644 doc/develop/package/devicetree.rst > > > > > > > > > > > > > > diff --git a/doc/develop/index.rst b/doc/develop/index.rst > > > > > > > index 83c929babda..d5ad8f9fe53 100644 > > > > > > > --- a/doc/develop/index.rst > > > > > > > +++ b/doc/develop/index.rst > > > > > > > @@ -36,6 +36,7 @@ Packaging > > > > > > > :maxdepth: 1 > > > > > > > > > > > > > > package/index > > > > > > > + package/devicetree > > > > > > > > > > > > > > Testing > > > > > > > ------- > > > > > > > diff --git a/doc/develop/package/devicetree.rst b/doc/develop= /package/devicetree.rst > > > > > > > new file mode 100644 > > > > > > > index 00000000000..fccbb182f3e > > > > > > > --- /dev/null > > > > > > > +++ b/doc/develop/package/devicetree.rst > > > > > > > @@ -0,0 +1,315 @@ > > > > > > > +.. SPDX-License-Identifier: GPL-2.0+ > > > > > > > + > > > > > > > +Updating the devicetree > > > > > > > +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D > > > > > > > + > > > > > > > +U-Boot uses devicetree for runtime configuration and storing= required blobs or > > > > > > > +any other information it needs to operate. It is possible to= update the > > > > > > > +devicetree separately from actually building U-Boot. This pr= ovides a good degree > > > > > > > +of control and flexibility for firmware that uses U-Boot in = conjunction with > > > > > > > +other project. > > > > > > > + > > > > > > > +There are many reasons why it is useful to modify the device= tree after building > > > > > > > +it: > > > > > > > + > > > > > > > +- Configuration can be changed, e.g. which UART to use > > > > > > > +- A serial number can be added > > > > > > > +- Public keys can be added to allow image verification > > > > > > > +- Console output can be changed (e.g. to select serial or vi= dconsole) > > > > > > > + > > > > > > > +This section describes how to work with devicetree to accomp= lish your goals. > > > > > > > + > > > > > > > +See also :doc:`../devicetree/control` for a basic summary of= the available > > > > > > > +features. > > > > > > > + > > > > > > > + > > > > > > > +Devicetree source > > > > > > > +----------------- > > > > > > > + > > > > > > > +Every board in U-Boot must include a devicetree sufficient t= o build and boot > > > > > > > +that board on suitable hardware (or emulation). This is spec= ified using the > > > > > > > +`CONFIG DEFAULT_DEVICE_TREE` option. > > > > > > > + > > > > > > > + > > > > > > > +Current situation (August 2021) > > > > > > > +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > > > > > > > + > > > > > > > +As an aside, at present U-Boot allows `CONFIG_DEFAULT_DEVICE= _TREE` to be empty, > > > > > > > +e.g. if `CONFIG_OF_BOARD` or `CONFIG_OF_PRIOR_STAGE` are use= d. This has > > > > > > > +unfortunately created an enormous amount of confusion and so= me wasted effort. > > > > > > > +This was not intended and this bug will be fixed soon. Speci= fically: > > > > > > > + > > > > > > > +- `CONFIG_OF_BOARD` was added in rpi_patch_ for Raspberry Pi= , which does have > > > > > > > + an in-tree devicetree, but this feature has since been use= d for boards that > > > > > > > + don't > > > > > > > +- `CONFIG_OF_PRIOR_STAGE` was added in bcm_patch_ as part of= a larger Broadcom > > > > > > > + change with a tag indicating it only affected one board, s= o the change in > > > > > > > + behaviour was not noticed at the time. It has since been u= sed by RISC-V qemu > > > > > > > + boards. > > > > > > > + > > > > > > > +Once this bug is fixed, CONFIG_OF_BOARD and CONFIG_OF_PRIOR_= STAGE will override > > > > > > > +(at runtime) the devicetree suppled with U-Boot, but will ot= herwise use > > > > > > > +CONFIG_OF_SEPARATE for the in-tree build. So these two will = become options, > > > > > > > +moving out of the 'choice' in `dts/Kconfig` > > > > > > > + > > > > > > > +Offending boards are: > > > > > > > + > > > > > > > +- bcm7260 > > > > > > > +- bcm7445 > > > > > > > +- qemu_arm64 > > > > > > > +- qemu_arm > > > > > > > +- qemu-ppce500 > > > > > > > +- qemu-riscv32 > > > > > > > +- qemu-riscv32_smode > > > > > > > +- qemu-riscv64 > > > > > > > +- qemu-riscv64_smode > > > > > > > + > > > > > > > +All of these need to have a devicetree added in-tree. This i= s targeted to be > > > > > > > +fixed in the 2022.01 release. > > > > > > > > > > > > Do you have some idea of how to support the QEMU case, if not u= sing > > > > > > CONFIG_OF_PRIOR_STAGE? > > > > > > > > > > To be clear, I am not planning to remove this option. It will sti= ll work. > > > > > > > > > > But I do want to have an in-tree devicetree for all boards, and > > > > > someone will need to update qemu to support adding U-Boot > > > > > nodes/properties. It always has an array of options controlling w= hat > > > > > it presents to BIOS/UEFI, for example, so this should not be too > > > > > controversial. > > > > > > > > I think there is some misunderstanding. > > > > > > > > Adding U-Boot nodes/properties is not a problem for QEMU, but the > > > > thing is that these QEMU targets don't require U-Boot specific > > > > nodes/properties. It's just that QEMU will generate the DTB on the = fly > > > > based on different command-line options, so the DTB is dynamic and = we > > > > can't hardcode one in the U-Boot tree. > > > > > > That's fine, but I do want some sort of sample in the tree, like we > > > have for qemu-x86 and others. For some reason ARM and RISC-V don't > > > have one. > > > > > > Also, QEMU needs a way to add properties and nodes that are specific > > > to U-Boot, since at present there is no way at all to pass these > > > through (/config node, u-boot,dm-xxx tags, etc.). > > > > I suppose some of the /config stuff could be nice and that the device > > tree is indeed the most appropriate way to pass runtime options from > > QEMU to U-Boot. But I'd say U-Boot should still work (with reasonable > > defaults) if no U-Boot specific options are present in the device > > tree. >=20 > Well I believe it does and actually I think CI currently checks > this.The config node is certainly optional. But it would not support > booting signed images, for example, without the public key. The public key would need to be included in what's passed to us, yes? --=20 Tom --W6sWy1GDZvBCAepP Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQGzBAABCgAdFiEEGjx/cOCPqxcHgJu/FHw5/5Y0tywFAmErndYACgkQFHw5/5Y0 tywV4wwAhkYgGifjFbaI4vjJebLDQiH0Xn8wbBv0dh/U/2stqtN7CSuabKbnAa7V fW0dbNkRZKyE6/ZPGOn0sMM/9GWS5rt5xX1MNE/vAweS/GcXvzQVCMTK6GYlivEN FVYVjs72agQqvxK4EmtglYj8QXCxJJaLuH0e+qAAbOZrkjZrS7wpZ85zK0uwzy2p UNosagTzUcp7eDYsqUTFJabVXRQZ1l3d55BatHj9mSxuvtcfASP5vHHEMQBWWMxo Cbj8YzBK03S8zVMvsqECCYTyybHUsuJzIffYYEcPEV1yndiDgYGADjrUoeiTM0Em afgfwIkHeQDIvtk8oOl7e8OWxT7KjkDeo6yEPRc/paq1mijcN9zWfgoRoJBb/DmP pNLv/C/8mUjuYwqf99VNynJNm7Tce4NeqCb1OYQEUvP5ahU6w2wmy6GXg0fGHXFT 5RW/LyK3jL9RWWBCHA87u+v4Q0e7zOnpmQCQw83nlUgy9SqjCkAkkJgrR3l3UFiY q5WqMDDu =eHpx -----END PGP SIGNATURE----- --W6sWy1GDZvBCAepP--