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 Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id AF564D46BE5 for ; Wed, 28 Jan 2026 17:48:47 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1vl9ed-0001C8-M7; Wed, 28 Jan 2026 12:48:36 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1vl9eY-00019m-MV for qemu-arm@nongnu.org; Wed, 28 Jan 2026 12:48:31 -0500 Received: from mail-wr1-x433.google.com ([2a00:1450:4864:20::433]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.90_1) (envelope-from ) id 1vl9eX-0001iQ-19 for qemu-arm@nongnu.org; Wed, 28 Jan 2026 12:48:30 -0500 Received: by mail-wr1-x433.google.com with SMTP id ffacd0b85a97d-4359a302794so106933f8f.1 for ; Wed, 28 Jan 2026 09:48:27 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; t=1769622507; x=1770227307; darn=nongnu.org; h=content-transfer-encoding:mime-version:message-id:date:user-agent :references:in-reply-to:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=bj5ufOGr/9lEHh2xwuGdrDse0fcL/BvnanZmIrsO+rg=; b=Dy0km1IDq0O81ntQ3cLsE3wN648ht+iySK6Qj6sH6sXASYIlP277SxKAlbNfW0bDC2 TU7e1PcTgyVPS4Br2DOUkJVA67SOd0tZ73IEs//IuwEhGGnvaSRZw04pA6XrusxFqYJK i4JuiJmkUr9LWV3pJYK3vJT+LDtANqKQq1tunPwDc90Jsd/mLGbtc2pD42wzKMAWhXuj FUSA+rxx4s6bhR/6lkCQYrfNvC8PFwTUnyqFbVDt5R4Rvxt+3/FZOXhH3DLapmW2Uzuh Epan2PweyZPgynCfv9/KkwkwYC6qzNwQOxBj/2xFyaurv4yAPZJqlubGP4tKh5XWXYcX dkbA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1769622507; x=1770227307; h=content-transfer-encoding:mime-version:message-id:date:user-agent :references:in-reply-to:subject:cc:to:from:x-gm-gg :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=bj5ufOGr/9lEHh2xwuGdrDse0fcL/BvnanZmIrsO+rg=; b=JEWlWtAUPlrmIW/eWbVtZ2TT5FxHFwo8EMNv6Ol7hamlAyfXOE2HC33HUqkpWvOIcO AKVShXm8g0x9b6hCVfqogeBP+it2tngjo08SpYJesGHR+NsUNQDYetr9Gtxe4Qryebs1 a7EwgqauUUbkOE8UXmqNpvcBjcqq+rCuVhwLHke5+CGWJDhaQXdyznzMVbvgxVd+X21y 1UDNe3JY/p5K8HCXkm+Gtm6pKDr4UVvCxK0kUwhnYCUv2XHvh1kThAUZ+uPqSfPOw1dv wrTa56l8aJ9cEIfv27Z/cKQiygzR+ng/BIkGbA3udUxtjD9y2Tnl5hyIrzHeQ9XyRthA PCfQ== X-Forwarded-Encrypted: i=1; AJvYcCUpta+/Tf0/o92lWyjWzWFMeLDi9IAJH/3tdFO/VUMngc+aDl9WJNlKq2Pip4pGR6CeETnOKIy16A==@nongnu.org X-Gm-Message-State: AOJu0YxEdLLaiMLvjPyXiLZdVkHPltJoD9HRHr/xuBuhAbk8FxaRlrXm Cy5gWSj0Hw2HoV51kzdPyoBo5rIVmTFRM8Xk/owS3EAiAjqV/uQVcYfUInLeTvp6+uLMPhbNVAz e6IvUmB4= X-Gm-Gg: AZuq6aLoH3TvS0JuhC4DHieJ417VpvKzu0/d6UwHoaJYp4yscRFzefmtFUO3tXu/kpj Uhmp0gnX1LXoU3PlPc7RJoSfG+YsBcghUIh/GfaKtVeLtwoVrBeKPaSWKVgQrghfpJQuOQhJ2ym 6MjLNLe4T4kBviWyvpk4psmHgfOyElIVG+mraG+zCGh33g4OB9JY4H7DxYhrWc3uTV6u/r19liP qfEGyGF6p7RGIlFCNbmRdrSFoH+Gl1/8Y2hgWtPcjmit5IwHBDXNFDy9yGRbAj6a7kvIc6V8pni 6Z+0Gk6J2a6rByhgNlI+wv2I310xj9d039goqSPvfptDdYu3480oNtK9rzR3rrv3mcLh5h5za+4 VI5YM/JegtYTbGkKKJoV7uho0HYsYMwKKz7iYaUg/9g8dUeuejsShirnErNkeQUzgGGsBYIO3NK dgRskm1U3qWcJtNl9ipdGJww== X-Received: by 2002:a05:6000:2081:b0:432:dfa8:e1b6 with SMTP id ffacd0b85a97d-435dd0b6a75mr9548688f8f.39.1769622506629; Wed, 28 Jan 2026 09:48:26 -0800 (PST) Received: from draig.lan ([185.124.0.126]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-435e131cfd4sm8218361f8f.25.2026.01.28.09.48.25 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 28 Jan 2026 09:48:25 -0800 (PST) Received: from draig (localhost [IPv6:::1]) by draig.lan (Postfix) with ESMTP id E3D155F895; Wed, 28 Jan 2026 17:48:24 +0000 (GMT) From: =?utf-8?Q?Alex_Benn=C3=A9e?= To: Ruslan Ruslichenko Cc: Peter Maydell , qemu-devel@nongnu.org, qemu-arm@nongnu.org, artem_mygaiev@epam.com, volodymyr_babchuk@epam.com, takahiro.nakata.wr@renesas.com, "Edgar E . Iglesias" , Ruslan_Ruslichenko@epam.com Subject: Re: [PATCH 00/27] hw/arm: Add generic FDT-based machine and infrastructure In-Reply-To: (Ruslan Ruslichenko's message of "Tue, 27 Jan 2026 19:18:10 +0100") References: <20260126174313.1418150-1-ruslichenko.r@gmail.com> User-Agent: mu4e 1.14.0-pre1; emacs 30.1 Date: Wed, 28 Jan 2026 17:48:24 +0000 Message-ID: <87ecn9aas7.fsf@draig.linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Received-SPF: pass client-ip=2a00:1450:4864:20::433; envelope-from=alex.bennee@linaro.org; helo=mail-wr1-x433.google.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-arm@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-arm-bounces+qemu-arm=archiver.kernel.org@nongnu.org Sender: qemu-arm-bounces+qemu-arm=archiver.kernel.org@nongnu.org Ruslan Ruslichenko writes: > On Tue, Jan 27, 2026 at 11:03=E2=80=AFAM Peter Maydell wrote: >> >> On Mon, 26 Jan 2026 at 17:43, Ruslan Ruslichenko >> wrote: >> > >> > From: Ruslan Ruslichenko >> > >> > This patch series introduces new ARM machine model, arm-generic-fdt, a= nd the underlying infrastructure required to instantiate a QEMU machine fro= m a Device Tree. >> >> I'm afraid this has been a feature that has been suggested from >> time to time, but which I don't think is workable in general. >> >> Device tree files are designed to provide enough information to >> the guest kernel to allow it to find non-probeable hardware. They >> are not designed to provide enough information to QEMU to allow >> it to create and wire up all the hardware present on the system. >> >> There are specific niches where it can be made to work -- I think >> Xilinx have or had a setup where they were generating an FPGA >> model and a device tree and a guest kernel all from the same >> single data source, so they could put everything necessary into >> the dtb, for example -- but I don't think it works in the >> general case. As one simple example, the DTB doesn't generally >> have any information about how the Secure world works in an Arm >> system, because Linux doesn't care about the Secure world. It >> also doesn't usually have information that the guest OS can >> probe for itself at runtime. >> >> There has been periodic discussion of more flexible user-driven >> board creation, but that has generally been with the idea of using >> the QMP monitor to orchestrate creation and connection of device >> models. >> > I agree that a guest Device Tree is insufficient for describing a > complete QEMU machine model. > However, we separate the guest configuration from the machine > definition. The -hw-dtb option allows the user to provide a > QEMU-specific system description. > Those hw-dtb would not be passed to Linux Guest VM. > > The fact that this workflow has been successfully used in production > by AMD/Xilinx demonstrates that FDT is a feasible format. Where are the extensions to the FDT used for hw-dtb documented? How does it deal with PCI devices and the Secure world? > In contrast, QMP usage may end up even more complex and less > maintainable for the task of full system modeling. > To my understanding, this would need to generate too long configs, > which may eventually require some intermediate format by itself. > > I am proposing to use FDT as a serialization format to describe a > machine configuration. Theoretically we can use other formats, like > XML, but in my opinion FDT perfectly matches the requirements. The QMP interface is self-documenting and introspectable and used for the management of QEMU including things like hotplug. It is also QOM aware so a natural fit for dealing with the underlying QOM machinery. Previous discussions have entertained the idea of making the parsing of hw-dtb an external script which would then translate into QMP commands to build up the machine. > > BR, > Ruslan Ruslichenko > > >> thanks >> -- PMM --=20 Alex Benn=C3=A9e Virtualisation Tech Lead @ Linaro