linux-kernel - Re: [PATCH v2 1/6] device property: Add functions for accessing node's parents

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Date:   Wed, 27 Mar 2019 13:26:25 +0100
From:   Petr Mladek <pmladek@...e.com>
To:     Sakari Ailus <sakari.ailus@...ux.intel.com>
Cc:     linux-kernel@...r.kernel.org, rafael@...nel.org,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        linux-acpi@...r.kernel.org, devicetree@...r.kernel.org,
        Rob Herring <robh@...nel.org>
Subject: Re: [PATCH v2 1/6] device property: Add functions for accessing
 node's parents

On Tue 2019-03-26 14:41:01, Sakari Ailus wrote:
> Add two convenience functions for accessing node's parents:
> 
> fwnode_count_parents() returns the number of parent nodes a given node
> has. fwnode_get_nth_parent() returns node's parent at a given distance
> from the node itself.
> 
> Also reorder fwnode_get_parent() in property.c according to the same order
> as in property.h.
> 
> diff --git a/drivers/base/property.c b/drivers/base/property.c
> index 8b91ab380d14..61eb6ceacc3f 100644
> --- a/drivers/base/property.c
> +++ b/drivers/base/property.c
> @@ -554,17 +567,49 @@ struct fwnode_handle *fwnode_get_next_parent(struct fwnode_handle *fwnode)
>  EXPORT_SYMBOL_GPL(fwnode_get_next_parent);
>  
>  /**
> - * fwnode_get_parent - Return parent firwmare node
> - * @fwnode: Firmware whose parent is retrieved
> + * fwnode_count_parents - Return the number of parents a node has
> + * @fwnode: The node the parents of which are to be counted
>   *
> - * Return parent firmware node of the given node if possible or %NULL if no
> - * parent was available.
> + * Returns the number of parents a node has.
>   */
> -struct fwnode_handle *fwnode_get_parent(const struct fwnode_handle *fwnode)
> +unsigned int fwnode_count_parents(struct fwnode_handle *fwnode)
>  {
> -	return fwnode_call_ptr_op(fwnode, get_parent);
> +	unsigned int count;
> +
> +	fwnode_handle_get(fwnode);
> +
> +	for (count = 0; fwnode; count++)
> +		fwnode = fwnode_get_next_parent(fwnode);

Is it guaranteed that all parents stay when
fwnode_get_next_parent() releases the reference count
for each counted member?

> +
> +	return count - 1;

We could start counting from count = -1;

>  }
> -EXPORT_SYMBOL_GPL(fwnode_get_parent);
> +EXPORT_SYMBOL_GPL(fwnode_count_parents);
> +

Best Regards,
Petr