linux-kernel - Re: [PATCH 1/6] arm64: Unconditionally call unflatten_device

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Date: Thu, 18 Jan 2024 17:23:28 +0100
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Mark Rutland <mark.rutland@....com>
Cc: Stephen Boyd <sboyd@...nel.org>, Rob Herring <robh+dt@...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>, 
	Will Deacon <will@...nel.org>
Subject: Re: [PATCH 1/6] arm64: Unconditionally call unflatten_device_tree()

Hi Mark,

On Thu, Jan 18, 2024 at 4:27 PM Mark Rutland <mark.rutland@....com> wrote:
> On Tue, Jan 16, 2024 at 05:27:18PM -0800, Stephen Boyd wrote:
> > Quoting Mark Rutland (2024-01-16 03:51:14)
> > > On Fri, Jan 12, 2024 at 12:07:44PM -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.
> > > > There's no harm in calling unflatten_device_tree() unconditionally.
> > >
> > > For better or worse, that's not true: there are systems the provide both a DTB
> > > *and* ACPI tables, and we must not consume both at the same time as those can
> > > clash and cause all sorts of problems. In addition, we don't want people being
> > > "clever" and describing disparate portions of their system in ACPI and DT.
> > >
> > > It is a very deliberate choice to not unflatten the DTB when ACPI is in use,
> > > and I don't think we want to reopen this can of worms.
> >
> > Hmm ok. I missed this part. Can we knock out the initial_boot_params in
> > this case so that we don't unflatten a DTB when ACPI is in use?
>
> Why is that better than just not calling unflatten_device_tree(), as we do
> today?
>
> The cover letter says this is all so that we can run DT tests for the clk
> framework; why can't that just depend on the system being booted with DT rather
> than ACPI? We have other tests which are architecture and/or configuration
> dependent...

There is definitely a merit in running (platform-independent) DT tests
on any platform, whether the platform actually uses DT to boot or not.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68korg

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds