linux-kernel - Re: [PATCH] of: WARN on using default root node #address-cells/#size-cells

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Date: Thu, 30 May 2024 19:33:57 -0500
From: Rob Herring <robh@...nel.org>
To: Conor Dooley <conor@...nel.org>
Cc: Saravana Kannan <saravanak@...gle.com>, Andreas Larsson <andreas@...sler.com>, 
	Sam Ravnborg <sam@...nborg.org>, sparclinux@...r.kernel.org, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] of: WARN on using default root node #address-cells/#size-cells

On Thu, May 30, 2024 at 2:21 PM Conor Dooley <conor@...nel.org> wrote:
>
> On Thu, May 30, 2024 at 01:50:48PM -0500, Rob Herring (Arm) wrote:
> > While OpenFirmware originally allowed default values of #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.
> >
> > I have no idea what exists for Sparc, so disabling the warning for it.
> > If any other platforms hit the warning, then the warning can be
> > disabled for them.
> >
> > Signed-off-by: Rob Herring (Arm) <robh@...nel.org>
> > ---
> > Sparc folks, If anyone can dump DTs from some Sparc systems it would be
> > helpful.
> > ---
> >  drivers/of/base.c | 2 ++
> >  drivers/of/fdt.c  | 2 ++
> >  2 files changed, 4 insertions(+)
> >
> > diff --git a/drivers/of/base.c b/drivers/of/base.c
> > index 61fff13bbee5..6930aa29fec1 100644
> > --- a/drivers/of/base.c
> > +++ b/drivers/of/base.c
> > @@ -96,6 +96,7 @@ int of_bus_n_addr_cells(struct device_node *np)
> >                       return cells;
> >
> >       /* No #address-cells property for the root node */
> > +     WARN_ONCE(!IS_ENABLED(CONFIG_SPARC), "Only listed platforms should rely on default '#address-cells'\n");
>
> I assume "listed platforms" means things in the first parameter of
> WARN_ONCE()? Since that's only SPARC, why not just say it? The error
> message is rather obtuse as-is I think.

My intent is if you hit this warning, add the platform here. I imagine
it will be older stuff we can't or don't want to fix. Maybe I should
just say that as a comment instead.

Rob