linux-kernel - Re: [PATCH v2] of: WARN on deprecated #address-cells/#size-cells handling

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Message-ID: <CAL_JsqLyFV85w1kf397AcvZ7+Oewpe3vYeZdz_uvQrYwb1B8ag@mail.gmail.com>
Date: Fri, 8 Nov 2024 08:04:42 -0600
From: Rob Herring <robh@...nel.org>
To: Steven Price <steven.price@....com>
Cc: Marek Szyprowski <m.szyprowski@...sung.com>, Saravana Kannan <saravanak@...gle.com>, 
	Krzysztof Kozlowski <krzk@...nel.org>, linuxppc-dev@...ts.ozlabs.org, 
	Conor Dooley <conor@...nel.org>, devicetree@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Linux Samsung SOC <linux-samsung-soc@...r.kernel.org>
Subject: Re: [PATCH v2] of: WARN on deprecated #address-cells/#size-cells handling

On Fri, Nov 8, 2024 at 7:26 AM Steven Price <steven.price@....com> wrote:
>
> On 08/11/2024 11:04, Marek Szyprowski wrote:
> > Hi Rob,
> >
> > On 06.11.2024 18:10, Rob Herring (Arm) wrote:
> >> While OpenFirmware originally allowed walking parent nodes and default
> >> root values for #address-cells and #size-cells, FDT has long required
> >> explicit values. It's been a warning in dtc for the root node since the
> >> beginning (2005) and for any parent node since 2007. Of course, not all
> >> FDT uses dtc, but that should be the majority by far. The various
> >> extracted OF devicetrees I have dating back to the 1990s (various
> >> PowerMac, OLPC, PASemi Nemo) all have explicit root node properties. The
> >> warning is disabled for Sparc as there are known systems relying on
> >> default root node values.
> >>
> >> Signed-off-by: Rob Herring (Arm) <robh@...nel.org>
> >> ---
> >> v2:
> >>   - Add a define for excluded platforms to help clarify the intent
> >>     is to have an exclude list and make adding platforms easier.
> >>   - Also warn when walking parent nodes.
> >> ---
> >>   drivers/of/base.c | 28 ++++++++++++++++++++++------
> >>   drivers/of/fdt.c  |  4 ++--
> >>   2 files changed, 24 insertions(+), 8 deletions(-)
> >
> > This patch landed in today's linux-next as commit 4b28a0dec185 ("of:
> > WARN on deprecated #address-cells/#size-cells handling"). In my tests I
> > found that it introduces warnings on almost all of my test systems. I
> > took a look at the first one I got in my logs (Samsung Exynos Rinato
> > board: arch/arm/boot/dts/samsung/exynos3250-rinato.dts):
>
> Just a "me too" for rk3288-firefly.dtb:
>
> [    0.138735] WARNING: CPU: 0 PID: 1 at drivers/of/base.c:106 of_bus_n_addr_cells+0x9c/0xd8
> [    0.138776] Missing '#address-cells' in /power-management@...30000
>
> I'm sure it's easy to fix up the DTB, but we shouldn't be breaking long existing DTBs.

What broke?

The intent here is to exclude any platforms/arch which actually need
the deprecated behavior, not change DTBs. That's spelled out at the
WARN which I assume people would read before fixing "Missing
'#address-cells' in /power-management@...30000". I tried to make the
warn message indicate that on v1 with:

WARN_ONCE(!IS_ENABLED(CONFIG_SPARC), "Only listed platforms should
rely on default '#address-cells'\n");

But Conor thought that wasn't clear. So I'm open to suggestions...

Rob