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

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Date: Thu, 18 Jan 2024 15:23:30 +0000
From: Mark Rutland <mark.rutland@....com>
To: Geert Uytterhoeven <geert@...ux-m68k.org>
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()

On Tue, Jan 16, 2024 at 03:13:42PM +0100, Geert Uytterhoeven wrote:
> Hi Mark,
> 
> On Tue, Jan 16, 2024 at 12:51 PM Mark Rutland <mark.rutland@....com> wrote:
> > 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.
> 
> We'd get to the latter anyway, when plugging in a USB device where the
> circuitry on/behind the USB device is described in DT.

I don't understand what you mean there; where is the DT description of the USB
device coming from if the DTB hasn't been unflattened?

Mark.