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Wed, 13 Oct 2021 14:06:20 -0400 Received: from mail-ua1-x92d.google.com ([2607:f8b0:4864:20::92d]:39617) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.90_1) (envelope-from ) id 1maidt-0007EF-3R for qemu-devel@nongnu.org; Wed, 13 Oct 2021 14:06:19 -0400 Received: by mail-ua1-x92d.google.com with SMTP id f3so6255979uap.6 for ; Wed, 13 Oct 2021 11:06:16 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc:content-transfer-encoding; bh=fTZCTjCyP5ueQtUS/8gGBZnW0PwaWtlLXVstgDV3oXU=; b=EW0Jqras34p84Xo3O39F0JD3jpJJMyY59aOC/TRfx4GkN4PjTAJ6/11HD4VUZWwHCU d1AnIPkRds28LM3dq3CQuy1Hyw468q4KoKg6EbhXrc9el/7+I7ZAP19eqe64fZNjYI9i rDhMA0xT7geazr3FP2dns6xqU3uYSqZRgpdWo= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc:content-transfer-encoding; bh=fTZCTjCyP5ueQtUS/8gGBZnW0PwaWtlLXVstgDV3oXU=; b=H1y12hpQzR1NN3e8jVu2dzQN9nRMb8v2GLE3MHI3eX/eMbOZjCWkHFYfa3vVQDp2o5 GylCrS/ktItw3kHdOlOLA8tC5kWYaZOWAhzRcSwffDcvnWU94fNWS+wj36G15fQq8sjX GSOC5TMvC/xsISKycFlHTXuRwuFTmTEn68Cgl0DGZb2fM68Qq8ZlvdQs+RUdoPkOxR2s eIH+qJSzvS4LppBm/flTXY+lL7vuEr3zkJageAWWggxdSfyeK/iB8Yu1SLw8bStAdB44 iSaHfagbFlClYWU+VqTUy9ouYe23gPjxfseDwipg0X2bhbc/g6dWryELw9Mg3Zyn+QWU m6/Q== X-Gm-Message-State: AOAM530kURgePxE7Ip1W/WsN/0Lk1+aesPVSaCi4eiHn2hQ3N2bgZ5gy NmxjHD2pEL5nFDBc0Vh+O+9qnRwgtiZOBa+kLH4SWw== X-Google-Smtp-Source: ABdhPJwevCp8qw/j778etF2R3Ok03g38DlcVUiAVlCLDqc2EYzcbzvoBpbr/im2zbggmZDMwrGP9knpUyS3KXGCm4RY= X-Received: by 2002:a67:c30b:: with SMTP id r11mr1194827vsj.20.1634148375375; Wed, 13 Oct 2021 11:06:15 -0700 (PDT) MIME-Version: 1.0 References: <20211013010120.96851-1-sjg@chromium.org> <20211013013450.GJ7964@bill-the-cat> In-Reply-To: From: Simon Glass Date: Wed, 13 Oct 2021 12:06:02 -0600 Message-ID: Subject: Re: [PATCH 00/16] fdt: Make OF_BOARD a boolean option To: =?UTF-8?Q?Fran=C3=A7ois_Ozog?= Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Received-SPF: pass client-ip=2607:f8b0:4864:20::92d; envelope-from=sjg@google.com; helo=mail-ua1-x92d.google.com X-Spam_score_int: -92 X-Spam_score: -9.3 X-Spam_bar: --------- X-Spam_report: (-9.3 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.049, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, HEADER_FROM_DIFFERENT_DOMAINS=0.249, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, USER_IN_DEF_SPF_WL=-7.5 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Liviu Dudau , Neil Armstrong , Vladimir Oltean , Linus Walleij , Bin Meng , Kever Yang , Sean Anderson , Atish Patra , Zong Li , Stefan Roese , Fabio Estevam , Rainer Boschung , Tom Rini , Stephen Warren , Oleksandr Andrushchenko , Heinrich Schuchardt , Niel Fourie , Michal Simek , =?UTF-8?B?TWFyZWsgQmVow7pu?= , Jerry Van Baren , Ramon Fried , Jagan Teki , Valentin Longchamp , Heiko Schocher , Peter Robinson , Sinan Akman , Thomas Fitzsimmons , Wolfgang Denk , Stephen Warren , "qemu-devel@nongnu.org Developers" , Andre Przywara , Tim Harvey , Ashok Reddy Soma , Rick Chen , Alexander Graf , Green Wan , T Karthik Reddy , Anastasiia Lukianenko , Albert Aribaud , Michal Simek , Matthias Brugger , Leo , Tero Kristo , U-Boot Mailing List , David Abdurachmanov , Priyanka Jain , Ilias Apalodimas , Christian Hewitt , Aaron Williams , Tuomas Tynkkynen , Heinrich Schuchardt , Tianrui Wei , Bin Meng , =?UTF-8?Q?Pali_Roh=C3=A1r?= , Dimitri John Ledkov , Padmarao Begari Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Hi Fran=C3=A7ois, On Wed, 13 Oct 2021 at 11:35, Fran=C3=A7ois Ozog = wrote: > > Hi Simon > > Le mer. 13 oct. 2021 =C3=A0 16:49, Simon Glass a =C3= =A9crit : >> >> Hi Tom, Bin,Fran=C3=A7ois, >> >> On Tue, 12 Oct 2021 at 19:34, Tom Rini wrote: >> > >> > On Wed, Oct 13, 2021 at 09:29:14AM +0800, Bin Meng wrote: >> > > Hi Simon, >> > > >> > > On Wed, Oct 13, 2021 at 9:01 AM Simon Glass wrote= : >> > > > >> > > > With Ilias' efforts we have dropped OF_PRIOR_STAGE and OF_HOSTFILE= so >> > > > there are only three ways to obtain a devicetree: >> > > > >> > > > - OF_SEPARATE - the normal way, where the devicetree is built a= nd >> > > > appended to U-Boot >> > > > - OF_EMBED - for development purposes, the devicetree is embedd= ed in >> > > > the ELF file (also used for EFI) >> > > > - OF_BOARD - the board figures it out on its own >> > > > >> > > > The last one is currently set up so that no devicetree is needed a= t all >> > > > in the U-Boot tree. Most boards do provide one, but some don't. So= me >> > > > don't even provide instructions on how to boot on the board. >> > > > >> > > > The problems with this approach are documented at [1]. >> > > > >> > > > In practice, OF_BOARD is not really distinct from OF_SEPARATE. Any= board >> > > > can obtain its devicetree at runtime, even it is has a devicetree = built >> > > > in U-Boot. This is because U-Boot may be a second-stage bootloader= and its >> > > > caller may have a better idea about the hardware available in the = machine. >> > > > This is the case with a few QEMU boards, for example. >> > > > >> > > > So it makes no sense to have OF_BOARD as a 'choice'. It should be = an >> > > > option, available with either OF_SEPARATE or OF_EMBED. >> > > > >> > > > This series makes this change, adding various missing devicetree f= iles >> > > > (and placeholders) to make the build work. >> > > >> > > Adding device trees that are never used sounds like a hack to me. >> > > >> > > For QEMU, device tree is dynamically generated on the fly based on >> > > command line parameters, and the device tree you put in this series >> > > has various hardcoded values which normally do not show up >> > > in hand-written dts files. >> > > >> > > I am not sure I understand the whole point of this. >> > >> > I am also confused and do not like the idea of adding device trees for >> > platforms that are capable of and can / do have a device tree to give = us >> > at run time. >> >> (I'll just reply to this one email, since the same points applies to >> all replies I think) >> >> I have been thinking about this and discussing it with people for a >> few months now. I've been signalling a change like this for over a >> month now, on U-Boot contributor calls and in discussions with Linaro >> people. I sent a patch (below) to try to explain things. I hope it is >> not a surprise! >> >> The issue here is that we need a devicetree in-tree in U-Boot, to >> avoid the mess that has been created by OF_PRIOR_STAGE, OF_BOARD, >> BINMAN_STANDALONE_FDT and to a lesser extent, OF_HOSTFILE. Between >> Ilias' series and this one we can get ourselves on a stronger footing. >> There is just OF_SEPARATE, with OF_EMBED for debugging/ELF use. >> For more context: >> >> http://patchwork.ozlabs.org/project/uboot/patch/20210919215111.3830278-3= -sjg@chromium.org/ >> >> BTW I did suggest to QEMU ARM that they support a way of adding the >> u-boot.dtsi but there was not much interest there (in fact the >> maintainer would prefer there was no special support even for booting >> Linux directly!) > > i understand their point of view and agree with it. >> >> But in any case it doesn't really help U-Boot. I >> think the path forward might be to run QEMU twice, once to get its >> generated tree and once to give the 'merged' tree with the U-Boot >> properties in it, if people want to use U-Boot features. >> >> I do strongly believe that OF_BOARD must be a run-time option, not a >> build-time one. It creates all sorts of problems and obscurity which >> have taken months to unpick. See the above patch for the rationale. >> >> To add to that rationale, OF_BOARD needs to be an option available to >> any board. At some point in the future it may become a common way >> things are done, e.g. TF-A calling U-Boot and providing a devicetree >> to it. It doesn't make any sense to have people decide whether or not >> to set OF_BOARD at build time, thus affecting how the image is put >> together. We'll end up with different U-Boot build targets like >> capricorn, capricorn_of_board and the like. It should be obvious where >> that will lead. Instead, OF_BOARD needs to become a commonly used >> option, perhaps enabled by most/all boards, so that this sort of build >> explosion is not needed. > > If you mean that when boards are by construction providing a DTB to U-Boo= t then I agree very much. But I don=E2=80=99t understand how the patch set = supports it as it puts dts files for those boards to be built. >> >> U-Boot needs to be flexible enough to >> function correctly in whatever runtime environment in which it finds >> itself. >> >> Also as binman is pressed into service more and more to build the >> complex firmware images that are becoming fashionable, it needs a >> definition (in the devicetree) that describes how to create the image. >> We can't support that unless we are building a devicetree, nor can the >> running program access the image layout without that information. >> >> Fran=C3=A7ois's point about 'don't use this with any kernel' is >> germane...but of course I am not suggesting doing that, since OF_BOARD >> is, still, enabled. We already use OF_BOARD for various boards that >> include an in-tree devicetree - Raspberry Pi 1, 2 and 3, for example >> (as I said in the cover letter "Most boards do provide one, but some >> don't."). So this series is just completing the picture by enforcing >> that *some sort* of devicetree is always present. > > That seems inconsistent with the OF_BOARD becomes the default. I think the key point that will get you closer to where I am on this issue, is that OF_BOARD needs to be a run-time option. At present it has build-time effects and this is quite wrong. If you go through all the material I have written on this I think I have motivated that very clearly. Another big issue is that I believe we need ONE devicetree for U-Boot, not two that get merged by U-Boot. Again I have gone through that in a lot of detail. >> >> >> I can't quite pinpoint the patch where U-Boot started allowing the >> devicetree to be omitted, but if people are interested I could try a >> little harder. It was certainly not my intention (putting on my >> device-tree-maintainer hat) to go down that path and it slipped in >> somehow in all the confusion. I'm not sure anyone could tell you that >> rpi_3 has an in-tree devicetree but rpi_4 does not... >> >> Anyway this series is very modest. It just adds the requirement that >> all in-tree boards have some sort of sample devicetree and preferably >> some documentation as to where it might come from at runtime. > > That=E2=80=99s a very good goal. But adding files in dts make them not sa= mples but templates to be used and replace board provided DTB. > If you push all your DTS files in documentation, you do what you say: add= ing sample files. >> >> That >> should not be a tough call IMO. Assuming we can get the validation in >> place (mentioned by Rob Herring recently) it will be quite natural to >> sync them between (presumably) Linux and U-Boot. >> >> I am also quite happy to discuss what should actually be in these >> devicetree files and whether some of them should be essentially empty. >> As you probably noticed, some of them are empty since I literally >> could not figure out where they come from! But there needs to be at >> least some skeleton for U-Boot to progress, since devicetree is >> critical to its feature set. > > absolutely. And thank you for your efforts to make that center stage. Thi= s is also Linaro Edge group mist challenging task on the next 6 moths. Kno= wing that we have lived in a floating situation for over 10 years, I just h= ope we get consensus across projects and distro providers about the right e= nd goal and migration strategy. >> Thank you. >> >> >> It is high time we tidied all this up. I predict it will be much >> harder, and much more confusing, in 6 months. Just to set a road map here in case you can help unblock anything, here are the things I am aware of, excluding the things I have forgotten: - Ilias OF_PRIOR_STAGE, OF_HOSTFILE series - this series - the devicetree docs patch - devicetree bindings upstream for U-Boot (first patch under discussion) - bloblist as a means of passing devicetree, ACPI, tiny config info as C structs to U-Boot (needs to be written) - VPL so we can handle verification (patches pending) - bootflow / VBE v2 series (coming next week) Regards, Simon