linux-kernel - Re: [PATCH v9 1/2] of_graph: add of_graph_is

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Date:   Wed, 1 Jul 2020 08:45:43 +0300
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Dmitry Osipenko <digetx@...il.com>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Sam Ravnborg <sam@...nborg.org>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        dri-devel@...ts.freedesktop.org, linux-tegra@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v9 1/2] of_graph: add of_graph_is_present()

Hi Dmitry,

Thank you for the patch.

On Wed, Jul 01, 2020 at 05:16:16AM +0300, Dmitry Osipenko wrote:
> In some case, like a DRM display code for example, it's useful to silently
> check whether port node exists at all in a device-tree before proceeding
> with parsing of the graph.
> 
> This patch adds of_graph_is_present() which returns true if given
> device-tree node contains OF graph port.
> 
> Reviewed-by: Rob Herring <robh@...nel.org>
> Signed-off-by: Dmitry Osipenko <digetx@...il.com>
> ---
>  drivers/of/property.c    | 52 +++++++++++++++++++++++++++++++++-------
>  include/linux/of_graph.h |  6 +++++
>  2 files changed, 49 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/of/property.c b/drivers/of/property.c
> index 6a5760f0d6cd..e12b8b491837 100644
> --- a/drivers/of/property.c
> +++ b/drivers/of/property.c
> @@ -29,6 +29,48 @@
>  
>  #include "of_private.h"
>  
> +/**
> + * of_graph_get_first_local_port() - get first local port node
> + * @node: pointer to a local endpoint device_node

It's not an endpoint.

> + *
> + * Return: First local port node associated with local endpoint node linked
> + *	   to @node. Use of_node_put() on it when done.
> + */
> +static struct device_node *
> +of_graph_get_first_local_port(const struct device_node *node)
> +{
> +	struct device_node *ports, *port;
> +
> +	ports = of_get_child_by_name(node, "ports");
> +	if (ports)
> +		node = ports;
> +
> +	port = of_get_child_by_name(node, "port");
> +	of_node_put(ports);
> +
> +	return port;
> +}
> +
> +/**
> + * of_graph_is_present() - check graph's presence
> + * @node: pointer to a device_node checked for the graph's presence
> + *
> + * Return: True if @node has a port or ports sub-node, false otherwise.
> + */
> +bool of_graph_is_present(const struct device_node *node)
> +{
> +	struct device_node *local;
> +
> +	local = of_graph_get_first_local_port(node);
> +	if (!local)
> +		return false;
> +
> +	of_node_put(local);
> +
> +	return true;
> +}
> +EXPORT_SYMBOL(of_graph_is_present);
> +
>  /**
>   * of_property_count_elems_of_size - Count the number of elements in a property
>   *
> @@ -608,15 +650,7 @@ struct device_node *of_graph_get_next_endpoint(const struct device_node *parent,
>  	 * parent port node.
>  	 */
>  	if (!prev) {
> -		struct device_node *node;
> -
> -		node = of_get_child_by_name(parent, "ports");
> -		if (node)
> -			parent = node;
> -
> -		port = of_get_child_by_name(parent, "port");
> -		of_node_put(node);
> -
> +		port = of_graph_get_first_local_port(parent);

I think this introduces a bug below in the function, where parent is
used and is expected to point to the ports node if available. I'd leave
this part of the change out, and inline +of_graph_get_first_local_port()
in of_graph_is_present().

>  		if (!port) {
>  			pr_err("graph: no port node found in %pOF\n", parent);
>  			return NULL;
> diff --git a/include/linux/of_graph.h b/include/linux/of_graph.h
> index 01038a6aade0..4d7756087b6b 100644
> --- a/include/linux/of_graph.h
> +++ b/include/linux/of_graph.h
> @@ -38,6 +38,7 @@ struct of_endpoint {
>  	     child = of_graph_get_next_endpoint(parent, child))
>  
>  #ifdef CONFIG_OF
> +bool of_graph_is_present(const struct device_node *node);
>  int of_graph_parse_endpoint(const struct device_node *node,
>  				struct of_endpoint *endpoint);
>  int of_graph_get_endpoint_count(const struct device_node *np);
> @@ -56,6 +57,11 @@ struct device_node *of_graph_get_remote_node(const struct device_node *node,
>  					     u32 port, u32 endpoint);
>  #else
>  
> +static inline bool of_graph_is_present(const struct device_node *node)
> +{
> +	return false;
> +}
> +
>  static inline int of_graph_parse_endpoint(const struct device_node *node,
>  					struct of_endpoint *endpoint)
>  {

-- 
Regards,

Laurent Pinchart