[v2,04/12] software_node: Enforce parent before child ordering of nodes arrays

Registering software_nodes with the .parent member set to point to a
currently unregistered software_node has the potential for problems,
so enforce parent -> child ordering in arrays passed in to
software_node_register_nodes().

Software nodes that are children of another software node should be
unregistered before their parent. To allow easy unregistering of an array
of software_nodes ordered parent to child, reverse the order in which
software_node_unregister_nodes() unregisters software_nodes.

Suggested-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Daniel Scally <djrscally@gmail.com>
---
Changes in v2:

	- Squashed the patches that originally touched these separately
	- Updated documentation

 drivers/base/swnode.c | 43 ++++++++++++++++++++++++++++++-------------
 1 file changed, 30 insertions(+), 13 deletions(-)

Hi Daniel,

Thank you for the patch.

On Thu, Dec 17, 2020 at 11:43:29PM +0000, Daniel Scally wrote:
> Registering software_nodes with the .parent member set to point to a
> currently unregistered software_node has the potential for problems,
> so enforce parent -> child ordering in arrays passed in to
> software_node_register_nodes().
> 
> Software nodes that are children of another software node should be
> unregistered before their parent. To allow easy unregistering of an array
> of software_nodes ordered parent to child, reverse the order in which
> software_node_unregister_nodes() unregisters software_nodes.
> 
> Suggested-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> Signed-off-by: Daniel Scally <djrscally@gmail.com>
> ---
> Changes in v2:
> 
> 	- Squashed the patches that originally touched these separately
> 	- Updated documentation
> 
>  drivers/base/swnode.c | 43 ++++++++++++++++++++++++++++++-------------
>  1 file changed, 30 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/base/swnode.c b/drivers/base/swnode.c
> index 615a0c93e116..cfd1faea48a7 100644
> --- a/drivers/base/swnode.c
> +++ b/drivers/base/swnode.c
> @@ -692,7 +692,10 @@ swnode_register(const struct software_node *node, struct swnode *parent,
>   * software_node_register_nodes - Register an array of software nodes
>   * @nodes: Zero terminated array of software nodes to be registered
>   *
> - * Register multiple software nodes at once.
> + * Register multiple software nodes at once. If any node in the array
> + * has it's .parent pointer set, then it's parent **must** have been
> + * registered before it is; either outside of this function or by
> + * ordering the array such that parent comes before child.
>   */
>  int software_node_register_nodes(const struct software_node *nodes)
>  {
> @@ -700,33 +703,47 @@ int software_node_register_nodes(const struct software_node *nodes)
>  	int i;
>  
>  	for (i = 0; nodes[i].name; i++) {
> -		ret = software_node_register(&nodes[i]);
> -		if (ret) {
> -			software_node_unregister_nodes(nodes);
> -			return ret;
> +		const struct software_node *parent = nodes[i].parent;
> +
> +		if (parent && !software_node_to_swnode(parent)) {
> +			ret = -EINVAL;
> +			goto err_unregister_nodes;
>  		}
> +
> +		ret = software_node_register(&nodes[i]);
> +		if (ret)
> +			goto err_unregister_nodes;
>  	}
>  
>  	return 0;
> +
> +err_unregister_nodes:
> +	software_node_unregister_nodes(nodes);
> +	return ret;
>  }
>  EXPORT_SYMBOL_GPL(software_node_register_nodes);
>  
>  /**
>   * software_node_unregister_nodes - Unregister an array of software nodes
> - * @nodes: Zero terminated array of software nodes to be unregistered
> + * @nodes: Zero terminated array of software nodes to be unregistered.

Not sure if this is needed.

>   *
> - * Unregister multiple software nodes at once.
> + * Unregister multiple software nodes at once. If parent pointers are set up
> + * in any of the software nodes then the array MUST be ordered such that

I'd either replace **must** above with MUST, or use **must** here. I'm
not sure if kerneldoc handles emphasis with **must**, if it does that
seems a bit nicer to me, but it's really up to you.

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

> + * parents come before their children.
>   *
> - * NOTE: Be careful using this call if the nodes had parent pointers set up in
> - * them before registering.  If so, it is wiser to remove the nodes
> - * individually, in the correct order (child before parent) instead of relying
> - * on the sequential order of the list of nodes in the array.
> + * NOTE: If you are uncertain whether the array is ordered such that
> + * parents will be unregistered before their children, it is wiser to
> + * remove the nodes individually, in the correct order (child before
> + * parent).
>   */
>  void software_node_unregister_nodes(const struct software_node *nodes)
>  {
> -	int i;
> +	unsigned int i = 0;
> +
> +	while (nodes[i].name)
> +		i++;
>  
> -	for (i = 0; nodes[i].name; i++)
> +	while (i--)
>  		software_node_unregister(&nodes[i]);
>  }
>  EXPORT_SYMBOL_GPL(software_node_unregister_nodes);