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

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Date: Thu, 30 May 2024 20:21:12 +0100
From: Conor Dooley <conor@...nel.org>
To: "Rob Herring (Arm)" <robh@...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 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.

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