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From: Geert Uytterhoeven <geert@linux-m68k.org>
Date: Thu, 18 Jan 2024 17:22:05 +0100
Message-ID: <CAMuHMdVW+zBU-7OEpsMZKFfkFbyN98jatG0RsLuzZmXKWavNAA@mail.gmail.com>
Subject: Re: [PATCH 1/6] arm64: Unconditionally call unflatten_device_tree()
To: Mark Rutland <mark.rutland@arm.com>
Cc: Stephen Boyd <sboyd@kernel.org>, Rob Herring <robh+dt@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>, 
	Will Deacon <will@kernel.org>
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Hi Mark,

On Thu, Jan 18, 2024 at 4:23=E2=80=AFPM Mark Rutland <mark.rutland@arm.com>=
 wrote:
> On Tue, Jan 16, 2024 at 03:13:42PM +0100, Geert Uytterhoeven wrote:
> > On Tue, Jan 16, 2024 at 12:51=E2=80=AFPM Mark Rutland <mark.rutland@arm=
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 DT=
B.
> > > > There's no harm in calling unflatten_device_tree() unconditionally.
> > >
> > > For better or worse, that's not true: there are systems the provide b=
oth a DTB
> > > *and* ACPI tables, and we must not consume both at the same time as t=
hose can
> > > clash and cause all sorts of problems. In addition, we don't want peo=
ple being
> > > "clever" and describing disparate portions of their system in ACPI an=
d 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 th=
e USB
> device coming from if the DTB hasn't been unflattened?

Either stored in (FLASH) ROM on the USB device, or loaded from
/lib/firmware/.  In both cases that would be handled by the USB driver
for the device.

Gr{oetje,eeting}s,

                        Geert

--=20
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k=
org

In personal conversations with technical people, I call myself a hacker. Bu=
t
when I'm talking to journalists I just say "programmer" or something like t=
hat.
                                -- Linus Torvalds