linux-kernel - Re: [PATCH v2] PCI: of: Downgrade error message on missing of

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Message-ID: <20251106002345.GA1934302@bhelgaas>
Date: Wed, 5 Nov 2025 18:23:45 -0600
From: Bjorn Helgaas <helgaas@...nel.org>
To: Andrea della Porta <andrea.porta@...e.com>
Cc: Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org, mbrugger@...e.com,
	guillaume.gardet@....com, tiwai@...e.com,
	Lizhi Hou <lizhi.hou@....com>
Subject: Re: [PATCH v2] PCI: of: Downgrade error message on missing of_root
 node

[+cc Lizhi]

On Wed, Nov 05, 2025 at 07:33:40PM +0100, Andrea della Porta wrote:
> When CONFIG_PCI_DYNAMIC_OF_NODES is enabled, an error message
> is generated if no 'of_root' node is defined.
> 
> On DT-based systems, this cannot happen as a root DT node is
> always present. On ACPI-based systems, this is not a true error
> because a DT is not used.
> 
> Downgrade the pr_err() to pr_info() and reword the message text
> to be less context specific.

of_pci_make_host_bridge_node() is called in the very generic
pci_register_host_bridge() path.  Does that mean every boot of a
kernel with CONFIG_PCI_DYNAMIC_OF_NODES on a non-DT system will see
this message?

This message seems like something that will generate user questions.
Or is this really an error, and we were supposed to have created
of_root somewhere but it failed?  If so, I would expect a message
where the of_root creation failed.

I guess I'm confused about what the point of this message is.  If it's
just a hint that loading an overlay in the future will fail, I assume
we would emit a message at that time, connected with the user action
of trying to load the overlay.

What badness would ensue if we downgraded this message even further
and removed it completely?

> Signed-off-by: Andrea della Porta <andrea.porta@...e.com>
> ---
> CHANGES in V2:
> 
> * message text reworded to be less context specific (Bjorn)
> ---
>  drivers/pci/of.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/of.c b/drivers/pci/of.c
> index 3579265f1198..872c36b195e3 100644
> --- a/drivers/pci/of.c
> +++ b/drivers/pci/of.c
> @@ -775,7 +775,7 @@ void of_pci_make_host_bridge_node(struct pci_host_bridge *bridge)
>  
>  	/* Check if there is a DT root node to attach the created node */
>  	if (!of_root) {
> -		pr_err("of_root node is NULL, cannot create PCI host bridge node\n");
> +		pr_info("Missing DeviceTree, cannot create PCI host bridge node\n");
>  		return;
>  	}
>  
> -- 
> 2.35.3
>