linux-kernel - Re: [PATCH 1/3] of: always populate a root node

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Message-ID: <YnEx5/ni1ddIFCj9@robh.at.kernel.org>
Date:   Tue, 3 May 2022 08:45:11 -0500
From:   Rob Herring <robh@...nel.org>
To:     Clément Léger <clement.leger@...tlin.com>
Cc:     Frank Rowand <frowand.list@...il.com>,
        Pantelis Antoniou <pantelis.antoniou@...sulko.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Allan Nielsen <allan.nielsen@...rochip.com>,
        Horatiu Vultur <horatiu.vultur@...rochip.com>,
        Steen Hegelund <steen.hegelund@...rochip.com>,
        Thomas Petazzoni <thomas.petazonni@...tlin.com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Mark Brown <broonie@...nel.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Hans de Goede <hdegoede@...hat.com>,
        Andrew Lunn <andrew@...n.ch>, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org
Subject: Re: [PATCH 1/3] of: always populate a root node

On Wed, Apr 27, 2022 at 11:45:00AM +0200, Clément Léger wrote:
> When enabling CONFIG_OF on a platform where of_root is not populated by
> firmware, we end up without a root node. In order to apply overlays and
> create subnodes of the root node, we need one. This commit creates an
> empty root node if not present.

The existing unittest essentially does the same thing for running the 
tests on non-DT systems. It should be modified to use this support 
instead. Maybe that's just removing the unittest code that set of_root.

I expect Frank will have some comments.

> Co-developed-by: Rob Herring <robh@...nel.org>
> Signed-off-by: Rob Herring <robh@...nel.org>
> Signed-off-by: Clément Léger <clement.leger@...tlin.com>
> ---
>  drivers/of/base.c | 16 ++++++++++++++--
>  1 file changed, 14 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/of/base.c b/drivers/of/base.c
> index e7d92b67cb8a..6b8584c39f73 100644
> --- a/drivers/of/base.c
> +++ b/drivers/of/base.c
> @@ -177,6 +177,19 @@ void __init of_core_init(void)
>  		pr_err("failed to register existing nodes\n");
>  		return;
>  	}
> +
> +	if (!of_root) {
> +		of_root = kzalloc(sizeof(*of_root), GFP_KERNEL);
> +		if (!of_root) {
> +			mutex_unlock(&of_mutex);
> +			pr_err("failed to create root node\n");
> +			return;
> +		}
> +
> +		of_root->full_name = "/";
> +		of_node_init(of_root);
> +	}
> +
>  	for_each_of_allnodes(np) {
>  		__of_attach_node_sysfs(np);
>  		if (np->phandle && !phandle_cache[of_phandle_cache_hash(np->phandle)])
> @@ -185,8 +198,7 @@ void __init of_core_init(void)
>  	mutex_unlock(&of_mutex);
>  
>  	/* Symlink in /proc as required by userspace ABI */
> -	if (of_root)
> -		proc_symlink("device-tree", NULL, "/sys/firmware/devicetree/base");
> +	proc_symlink("device-tree", NULL, "/sys/firmware/devicetree/base");
>  }
>  
>  static struct property *__of_find_property(const struct device_node *np,
> -- 
> 2.34.1
> 
>