linux-kernel - Re: [PATCH v4 5/7] arm64: Unconditionally call unflatten_device

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Date: Fri, 23 Feb 2024 11:17:02 -0700
From: Rob Herring <robh@...nel.org>
To: Will Deacon <will@...nel.org>
Cc: Stephen Boyd <sboyd@...nel.org>, linux-kernel@...r.kernel.org, patches@...ts.linux.dev, 
	linux-um@...ts.infradead.org, linux-arm-kernel@...ts.infradead.org, 
	kunit-dev@...glegroups.com, linux-kselftest@...r.kernel.org, 
	devicetree@...r.kernel.org, Frank Rowand <frowand.list@...il.com>, 
	Catalin Marinas <catalin.marinas@....com>, Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH v4 5/7] arm64: Unconditionally call unflatten_device_tree()

On Fri, Feb 23, 2024 at 3:23 AM Will Deacon <will@...nel.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 DTB
> > > 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 be
> > > 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 root
> > > one) and copy the 'initial_boot_params' data.
> > >
> > > Cc: Rob Herring <robh+dt@...nel.org>
> > > Cc: Frank Rowand <frowand.list@...il.com>
> > > Cc: Catalin Marinas <catalin.marinas@....com>
> > > Cc: Will Deacon <will@...nel.org>
> > > Cc: Mark Rutland <mark.rutland@....com>
> > > Cc: <linux-arm-kernel@...ts.infradead.org>
> > > Signed-off-by: Stephen Boyd <sboyd@...nel.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 the
> > 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