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From: Rob Herring <robh@kernel.org>
Date: Fri, 23 Feb 2024 11:17:02 -0700
Message-ID: <CAL_JsqJSeSHeWV3YJE9n2NuY+s_iE6f7N5C_oguEJn7jTZ20xA@mail.gmail.com>
Subject: Re: [PATCH v4 5/7] arm64: Unconditionally call unflatten_device_tree()
To: Will Deacon <will@kernel.org>
Cc: Stephen Boyd <sboyd@kernel.org>, 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 <frowand.list@gmail.com>, 
	Catalin Marinas <catalin.marinas@arm.com>, Mark Rutland <mark.rutland@arm.com>
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On Fri, Feb 23, 2024 at 3:23=E2=80=AFAM Will Deacon <will@kernel.org> wrote=
:
>
> On Thu, Feb 22, 2024 at 05:03:17PM -0700, Rob Herring wrote:
> > On Fri, Feb 16, 2024 at 05:05:54PM -0800, Stephen Boyd wrote:
> > > Call this function unconditionally so that we can populate an empty D=
TB
> > > on platforms that don't boot with a firmware provided or builtin DTB.
> > > When ACPI is in use, unflatten_device_tree() ignores the
> > > 'initial_boot_params' pointer so the live DT on those systems won't b=
e
> > > whatever that's pointing to. Similarly, when kexec copies the DT data
> > > the previous kernel to the new one on ACPI systems,
> > > of_kexec_alloc_and_setup_fdt() will ignore the live DT (the empty roo=
t
> > > one) and copy the 'initial_boot_params' data.
> > >
> > > Cc: Rob Herring <robh+dt@kernel.org>
> > > Cc: Frank Rowand <frowand.list@gmail.com>
> > > Cc: Catalin Marinas <catalin.marinas@arm.com>
> > > Cc: Will Deacon <will@kernel.org>
> > > Cc: Mark Rutland <mark.rutland@arm.com>
> > > Cc: <linux-arm-kernel@lists.infradead.org>
> > > Signed-off-by: Stephen Boyd <sboyd@kernel.org>
> > > ---
> > >  arch/arm64/kernel/setup.c | 3 +--
> > >  1 file changed, 1 insertion(+), 2 deletions(-)
> >
> > Catalin, Will, Can I get an ack on this so I can take the series via th=
e
> > DT tree.
>
> Mark had strong pretty strong objections to this in version one:

Yes, I had concerns with it as well.

> https://lore.kernel.org/all/ZaZtbU9hre3YhZam@FVFF77S0Q05N/
>
> and this patch looks the same now as it did then. Did something else
> change?

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.

Rob