linux-kernel - Re: [PATCH 2/3] of: Make of_find_node_by

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Date:	Thu, 15 May 2014 19:51:17 -0700
From:	Frank Rowand <frowand.list@...il.com>
To:	Grant Likely <grant.likely@...aro.org>
CC:	linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
	David Daney <david.daney@...ium.com>,
	Pantelis Antoniou <pantelis.antoniou@...sulko.com>
Subject: Re: [PATCH 2/3] of: Make of_find_node_by_path() handle /aliases

On 5/13/2014 7:58 AM, Grant Likely wrote:
> Make of_find_node_by_path() handle aliases as prefixes. To make this
> work the name search is refactored to search by path component instead
> of by full string. This should be a more efficient search, and it makes
> it possible to start a search at a subnode of a tree.
> 
> Signed-off-by: David Daney <david.daney@...ium.com>
> Signed-off-by: Pantelis Antoniou <pantelis.antoniou@...sulko.com>
> [grant.likely: Rework to not require allocating at runtime]
> Acked-by: Rob Herring <robh@...nel.org>
> Signed-off-by: Grant Likely <grant.likely@...aro.org>
> ---
>  drivers/of/base.c | 60 +++++++++++++++++++++++++++++++++++++++++++++++++++----
>  1 file changed, 56 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/of/base.c b/drivers/of/base.c
> index 6e240698353b..60089b9a3014 100644
> --- a/drivers/of/base.c
> +++ b/drivers/of/base.c
> @@ -771,9 +771,38 @@ struct device_node *of_get_child_by_name(const struct device_node *node,
>  }
>  EXPORT_SYMBOL(of_get_child_by_name);
>  
> +static struct device_node *__of_find_node_by_path(struct device_node *parent,
> +						const char *path)
> +{
> +	struct device_node *child;
> +	int len = strchrnul(path, '/') - path;
> +
> +	if (!len)
> +		return parent;

(!len) is true if the the final character of the path passed into of_find_node_by_path()
was "/".  Strictly speaking, ->full_name will never end with "/", so the return value
should be NULL, indicating that the match fails.

> +
> +	for_each_child_of_node(parent, child) {
> +		const char *name = strrchr(child->full_name, '/');
> +		if (WARN(!name, "malformed device_node %s\n", child->full_name))
> +			continue;
> +		name++;

Why go to the effort of finding the final component of child->full_name instead
of just using child->name?

> +		if (strncmp(path, name, len) == 0 && (strlen(name) == len))
> +			return child;
> +	}
> +	return NULL;
> +}
> +
>  /**
>   *	of_find_node_by_path - Find a node matching a full OF path
>   *	@path:	The full path to match
> + *	@path: Either the full path to match, or if the path does not

Delete the old @path description.


> + *	       start with '/', the name of a property of the /aliases
> + *	       node (an alias).  In the case of an alias, the node
> + *	       matching the alias' value will be returned.
> + *
> + *	Valid paths:
> + *		/foo/bar	Full path
> + *		foo		Valid alias
> + *		foo/bar		Valid alias + relative path
>   *
>   *	Returns a node pointer with refcount incremented, use
>   *	of_node_put() on it when done.
> @@ -781,13 +810,36 @@ EXPORT_SYMBOL(of_get_child_by_name);
>  struct device_node *of_find_node_by_path(const char *path)
>  {
>  	struct device_node *np = of_allnodes;
> +	struct property *pp;
>  	unsigned long flags;
>  
> +	/* The path could begin with an alias */
> +	if (*path != '/') {
> +		char *p = strchrnul(path, '/');
> +		int len = p - path;
> +
> +		/* of_aliases must not be NULL */
> +		if (!of_aliases)
> +			return NULL;
> +
> +		np = NULL;
> +		for_each_property_of_node(of_aliases, pp) {
> +			if (strlen(pp->name) == len && !strncmp(pp->name, path, len)) {
> +				np = of_find_node_by_path(pp->value);
> +				break;
> +			}
> +		}
> +		if (!np)
> +			return NULL;
> +		path = p;
> +	}
> +
> +	/* Step down the tree matching path components */
>  	raw_spin_lock_irqsave(&devtree_lock, flags);
> -	for (; np; np = np->allnext) {
> -		if (np->full_name && (of_node_cmp(np->full_name, path) == 0)
> -		    && of_node_get(np))
> -			break;
> +	while (np && *path == '/') {
> +		path++; /* Increment past '/' delimiter */
> +		np = __of_find_node_by_path(np, path);
> +		path = strchrnul(path, '/');
>  	}
>  	raw_spin_unlock_irqrestore(&devtree_lock, flags);
>  	return np;
> 

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