From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from relay2-d.mail.gandi.net (relay2-d.mail.gandi.net [217.70.183.194]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8BFFD12DD99 for ; Thu, 7 Mar 2024 15:09:46 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.70.183.194 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1709824189; cv=none; b=UWKu6j9IUMk5VfAznU3XRW7YgEl6Yg/KsAx4avXI/MP3lFVtllVeX37GznpZNmvPJalV3aiHgtiNhxks3KHRCxwbnqOS8xiztqud7WAc6LBsSPHOXhSWnJA/Xh2ldh/lI6Rf/69AttoyZZ2PZaRTXznytki+TUy5nMZi7xDLOlU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1709824189; c=relaxed/simple; bh=TOUq4+BzvbJ03xI0Ru4on6BK0VEShUhAYEA+2ftljxA=; h=Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=JL+qxiTpjmpZ5109m0bG3sOloGnF+wzV0VOrFwj3ptlvtnz7M41BtF4n9zbrCOXPv2VpmLEi9a3O0Iry+t0z3Y4RsnD7WJ3Y4BcMJYrkEO1biM0Ttr9iaXSlU+zex6te/PNhIBfxniWvsmMrGeESEG6v2BJaO9HMNsXPF/rRgCc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=bootlin.com; spf=pass smtp.mailfrom=bootlin.com; dkim=pass (2048-bit key) header.d=bootlin.com header.i=@bootlin.com header.b=cH3cDvDb; arc=none smtp.client-ip=217.70.183.194 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=bootlin.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=bootlin.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=bootlin.com header.i=@bootlin.com header.b="cH3cDvDb" Received: by mail.gandi.net (Postfix) with ESMTPSA id 517A640006; Thu, 7 Mar 2024 15:09:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bootlin.com; s=gm1; t=1709824184; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=P2YO5EELAYFm2yHbvmttaH3RlP1nT/5fz22vnvi4dvY=; b=cH3cDvDbgBL0NwR+c5yiG07kGF1VG+NjMPxfv/14+x0dhsSeDGuEwKCeaNb6jdZFkyzY+D La574Nc459V7/R01jXDg65BqvQHSmDykxG1XN8qBEbR7CVyi5obOAsTVQOKGfwbfehbPte Mh0Rc0OW1+VPfm1pV4+gARrMcjXqI+AHkuJweh3vf/IXXHCsEAYopHtavTyWsjxj5Ymp3B qjyrtvBI56L6eAKynWEsBr24gr7YfyTIj8DST6C37GKAqfAlQlB+BAjVOshLXP7/h/36ne 9dU5FIm9TCbBW0wYH2ekS1iqQOxe1zEUZ5Iak1MgQMMU5guelZJgniKPbafseA== Date: Thu, 7 Mar 2024 16:09:40 +0100 From: Herve Codina To: Rob Herring Cc: Mark Rutland , Will Deacon , Stephen Boyd , linux-kernel@vger.kernel.org, patches@lists.linux.dev, linux-um@lists.infradead.org, linux-arm-kernel@lists.infradead.org, kunit-dev@googlegroups.com, linux-kselftest@vger.kernel.org, devicetree@vger.kernel.org, Frank Rowand , Catalin Marinas , Thomas Petazzoni Subject: Re: [PATCH v4 5/7] arm64: Unconditionally call unflatten_device_tree() Message-ID: <20240307160940.6484ef8d@bootlin.com> In-Reply-To: <20240228162647.GA4086865-robh@kernel.org> References: <20240217010557.2381548-1-sboyd@kernel.org> <20240217010557.2381548-6-sboyd@kernel.org> <20240223000317.GA3835346-robh@kernel.org> <20240223102345.GA10274@willie-the-truck> <20240228162647.GA4086865-robh@kernel.org> Organization: Bootlin X-Mailer: Claws Mail 4.2.0 (GTK 3.24.41; x86_64-redhat-linux-gnu) Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-GND-Sasl: herve.codina@bootlin.com Hi, On Wed, 28 Feb 2024 10:26:47 -0600 Rob Herring wrote: ... > > > > > > Yes, that version unflattened the bootloader passed DT. Now within > > > unflatten_devicetree(), the bootloader DT is ignored if ACPI is > > > enabled and we unflatten an empty tree. That will prevent the kernel > > > getting 2 h/w descriptions if/when a platform does such a thing. Also, > > > kexec still uses the bootloader provided DT as before. > > > > That avoids the main instance of my concern, and means that this'll boot > > without issue, but IIUC this opens the door to dynamically instantiating DT > > devices atop an ACPI base system, which I think in general is something that's > > liable to cause more problems than it solves. > > > > I understand that's desireable for the selftests, though I still don't believe > > it's strictly necessary -- there are plenty of other things that only work if > > the kernel is booted in a specific configuration. > > Why add to the test matrix if we don't have to? > > > Putting the selftests aside, why do we need to do this? Is there any other > > reason to enable this? > > See my Plumbers talk... > > Or in short, there's 3 main usecases: > > - PCI FPGA card with devices instantiated in it > - SoCs which expose their peripherals via a PCI endpoint. > - Injecting test devices with QEMU (testing, but not what this series > does. Jonathan Cameron's usecase) > > In all cases, drivers already exist for the devices, and they often only > support DT. DT overlays is the natural solution for this, and there's > now kernel support for it (dynamically generating PCI DT nodes when they > don't exist). The intent is to do the same thing on ACPI systems. > > I don't see another solution other than 'go away, you're crazy'. There's > ACPI overlays, but that's only a debug feature. Also, that would > encourage more of the DT bindings in ACPI which I find worse than this > mixture. There's swnodes, but that's just board files and platform_data > 2.0. > > I share the concerns with mixing, but I don't see a better solution. The > scope of what's possible is contained enough to avoid issues. > I tested on a x86 system. My use case is 'SoCs which expose their peripherals via a PCI endpoint' described by Rob. Indeed, I have a Microchip Lan9662 board (the one mentioned by Rob in his Plumbers talk) and the root DT node creation is obviously needed. I have previously used Frank Rowan's patches [1] that did this DT root node creation. This series perfectly replace them and the root DT node is successfully created. Tested-by: Herve Codina [1]: https://lore.kernel.org/all/20230317053415.2254616-1-frowand.list@gmail.com/ Best regards, Hervé Codina -- Hervé Codina, Bootlin Embedded Linux and Kernel engineering https://bootlin.com