linux-kernel - Re: [PATCH v2 2/2] of/fdt: Restore possibility to use both ACPI and FDT from bootloader

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Message-ID: <173775582906.2508547.16287496501873966942.robh@kernel.org>
Date: Fri, 24 Jan 2025 15:57:12 -0600
From: "Rob Herring (Arm)" <robh@...nel.org>
To: Dmytro Maluka <dmaluka@...omium.org>
Cc: Thomas Gleixner <tglx@...utronix.de>,
	Bartłomiej Grzesik <bgrzesik@...gle.com>,
	Shikha Panwar <shikhapanwar@...gle.com>, x86@...nel.org,
	devicetree@...r.kernel.org,
	Pierre-Clément Tosi <ptosi@...gle.com>,
	Saurabh Sengar <ssengar@...ux.microsoft.com>,
	Grzegorz Jaszczyk <jaszczyk@...gle.com>,
	Keir Fraser <keirf@...gle.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Michal Mazurek <mazurekm@...gle.com>,
	Borislav Petkov <bp@...en8.de>, Will Deacon <will@...nel.org>,
	Usama Arif <usamaarif642@...il.com>,
	Stephen Boyd <sboyd@...nel.org>, "H. Peter Anvin" <hpa@...or.com>,
	Tomasz Nowicki <tnowicki@...gle.com>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	Frank Rowand <frowand.list@...il.com>,
	Saravana Kannan <saravanak@...gle.com>
Subject: Re: [PATCH v2 2/2] of/fdt: Restore possibility to use both ACPI and
 FDT from bootloader


On Sun, 05 Jan 2025 17:27:41 +0000, Dmytro Maluka wrote:
> There are cases when the bootloader provides information to the kernel
> in both ACPI and DTB, not interchangeably. One such use case is virtual
> machines in Android. When running on x86, the Android Virtualization
> Framework (AVF) boots VMs with ACPI like it is usually done on x86 (i.e.
> the virtual LAPIC, IOAPIC, HPET, PCI MMCONFIG etc are described in ACPI)
> but also passes various AVF-specific boot parameters in DTB. This allows
> reusing the same implementations of various AVF components on both
> arm64 and x86.
> 
> Commit 7b937cc243e5 ("of: Create of_root if no dtb provided by firmware")
> removed the possibility to do that, since among other things
> it introduced forcing emptying the bootloader-provided DTB if ACPI is
> enabled (probably assuming that if ACPI is available, a DTB can only be
> useful for applying overlays to it afterwards, for testing purposes).
> 
> So restore this possibility. Instead of completely preventing using ACPI
> and DT together, rely on arch-specific setup code to prevent using both
> to set up the same things (see various acpi_disabled checks under arch/).
> 
> Fixes: 7b937cc243e5 ("of: Create of_root if no dtb provided by firmware")
> Signed-off-by: Dmytro Maluka <dmaluka@...omium.org>
> ---
>  drivers/of/fdt.c | 10 +---------
>  1 file changed, 1 insertion(+), 9 deletions(-)
> 

Applied, thanks!