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

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Message-ID: <ZalDM90KoQ2Il0j7@FVFF77S0Q05N.cambridge.arm.com>
Date: Thu, 18 Jan 2024 15:26:43 +0000
From: Mark Rutland <mark.rutland@....com>
To: Stephen Boyd <sboyd@...nel.org>
Cc: 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()

On Tue, Jan 16, 2024 at 05:27:18PM -0800, Stephen Boyd wrote:
> Quoting Mark Rutland (2024-01-16 03:51:14)
> > Hi Stephen,
> > 
> > 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...

Mark.