From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-13.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5CE80C432BE for ; Sun, 29 Aug 2021 08:20:06 +0000 (UTC) Received: from phobos.denx.de (phobos.denx.de [85.214.62.61]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id B78E660F36 for ; Sun, 29 Aug 2021 08:20:04 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org B78E660F36 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=xs4all.nl Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=lists.denx.de Received: from h2850616.stratoserver.net (localhost [IPv6:::1]) by phobos.denx.de (Postfix) with ESMTP id DFFE882DC1; Sun, 29 Aug 2021 10:20:00 +0200 (CEST) Authentication-Results: phobos.denx.de; dmarc=fail (p=none dis=none) header.from=xs4all.nl Authentication-Results: phobos.denx.de; spf=pass smtp.mailfrom=u-boot-bounces@lists.denx.de Received: by phobos.denx.de (Postfix, from userid 109) id AF4DE82E04; Sun, 29 Aug 2021 10:19:59 +0200 (CEST) Received: from sibelius.xs4all.nl (sibelius.xs4all.nl [83.163.83.176]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits)) (No client certificate requested) by phobos.denx.de (Postfix) with ESMTPS id A038382C45 for ; Sun, 29 Aug 2021 10:19:55 +0200 (CEST) Authentication-Results: phobos.denx.de; dmarc=fail (p=none dis=none) header.from=xs4all.nl Authentication-Results: phobos.denx.de; spf=fail smtp.mailfrom=mark.kettenis@xs4all.nl Received: from localhost (bloch.sibelius.xs4all.nl [local]) by bloch.sibelius.xs4all.nl (OpenSMTPD) with ESMTPA id f3bab686; Sun, 29 Aug 2021 10:19:53 +0200 (CEST) Date: Sun, 29 Aug 2021 10:19:53 +0200 (CEST) From: Mark Kettenis To: Simon Glass Cc: bmeng.cn@gmail.com, u-boot@lists.denx.de, trini@konsulko.com, xypron.glpk@gmx.de, seanga2@gmail.com In-Reply-To: (message from Simon Glass on Sat, 28 Aug 2021 20:07:27 -0600) Subject: Re: [PATCH] doc: Add documentation about devicetree usage References: <20210828032348.4570-1-sjg@chromium.org> Message-ID: <5614245d41c45ae2@bloch.sibelius.xs4all.nl> 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 > 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 wrote: > > > > > > 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 cover how > > > > > devicetree is build, how it can be modified and the rules about 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 > > > > > +======================= > > > > > + > > > > > +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 provides 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 devicetree 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 vidconsole) > > > > > + > > > > > +This section describes how to work with devicetree to accomplish 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 to build and boot > > > > > +that board on suitable hardware (or emulation). This is specified 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 used. This has > > > > > +unfortunately created an enormous amount of confusion and some wasted effort. > > > > > +This was not intended and this bug will be fixed soon. Specifically: > > > > > + > > > > > +- `CONFIG_OF_BOARD` was added in rpi_patch_ for Raspberry Pi, which does have > > > > > + an in-tree devicetree, but this feature has since been used 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, so the change in > > > > > + behaviour was not noticed at the time. It has since been used 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 otherwise 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 is targeted to be > > > > > +fixed in the 2022.01 release. > > > > > > > > Do you have some idea of how to support the QEMU case, if not using > > > > CONFIG_OF_PRIOR_STAGE? > > > > > > To be clear, I am not planning to remove this option. It will still 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 what > > > 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. My understanding is that the u-boot,dm-xxx tags are for SPL. It seems that for most scenarios having where there is some prior firmware that passes a device tree, SPL isn't used. That certainly is the case for QEMU, Raspberry Pi and my Apple M1 work. > Perhaps something like the -dtb option that it already has, but just > for something to merge with what it uses. > > > My understanding is that we should remove CONFIG_OF_BOARD but keep > > CONFIG_OF_PRIOR_STAGE for such use case like QEMU. > > Fair enough if OF_BOARD is basically a duplicate. I'm actually not sure... > > Regards, > SImon