[PATCH v9 0/2] Silence missing-graph error for DRM bridges

[PATCH v9 0/2] Silence missing-graph error for DRM bridges

[Dmitry Osipenko]

Hi!

This small series improves DRM bridges code by silencing a noisy error
coming from of-graph code for the device-trees that are missing a
display bridge graph.

  graph: no port node found in ...

One example where this error happens is an older bridge-less DTB used
in conjunction with a newer kernel which has a display controller driver
that supports DRM bridges.

Changelog:

v9: - These two patches are factored out from [1] in order to ease applying
      of the patches.

    - The of_graph_presents() is renamed to of_graph_is_present() like it
      was requested by Rob Herring in the review comment to [1].

    - Added Rob's r-b.

    [1] https://patchwork.ozlabs.org/project/linux-tegra/list/?series=184102

Dmitry Osipenko (2):
  of_graph: add of_graph_is_present()
  drm/of: Make drm_of_find_panel_or_bridge() to check graph's presence

 drivers/gpu/drm/drm_of.c |  9 +++++++
 drivers/of/property.c    | 52 +++++++++++++++++++++++++++++++++-------
 include/linux/of_graph.h |  6 +++++
 3 files changed, 58 insertions(+), 9 deletions(-)

-- 
2.26.0

[PATCH v9 1/2] of_graph: add of_graph_is_present()

[Dmitry Osipenko]

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@kernel.org>
Signed-off-by: Dmitry Osipenko <digetx@gmail.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
+ *
+ * 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);
 		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)
 {
-- 
2.26.0

Re: [PATCH v9 1/2] of_graph: add of_graph_is_present()

[Laurent Pinchart]

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@kernel.org>
> Signed-off-by: Dmitry Osipenko <digetx@gmail.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

Re: [PATCH v9 1/2] of_graph: add of_graph_is_present()

[Dmitry Osipenko]

01.07.2020 08:45, Laurent Pinchart пишет:
> 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@kernel.org>
>> Signed-off-by: Dmitry Osipenko <digetx@gmail.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.

Alright, somehow I was reading this as a "device_node that contains
endpoint (of the graph)". But after re-reading twice I can see that it's
not the case.

It should be a "pointer to device_node containing graph port", just like
the of_graph_get_remote_node() says it. Thank you :)

>> + *
>> + * 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().

Good catch! I'll correct this.

Thank you for the review :)

[PATCH v9 2/2] drm/of: Make drm_of_find_panel_or_bridge() to check graph's presence

[Dmitry Osipenko]

When graph isn't defined in a device-tree, the of_graph_get_remote_node()
prints a noisy error message, telling that port node is not found. This is
undesirable behaviour in our case because absence of a panel/bridge graph
is a valid case. Let's check the graph's presence in a device-tree before
proceeding with parsing of the graph.

Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
---
 drivers/gpu/drm/drm_of.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/gpu/drm/drm_of.c b/drivers/gpu/drm/drm_of.c
index b50b44e76279..fdb05fbf72a0 100644
--- a/drivers/gpu/drm/drm_of.c
+++ b/drivers/gpu/drm/drm_of.c
@@ -246,6 +246,15 @@ int drm_of_find_panel_or_bridge(const struct device_node *np,
 	if (panel)
 		*panel = NULL;
 
+	/*
+	 * of_graph_get_remote_node() produces a noisy error message if port
+	 * node isn't found and the absence of the port is a legit case here,
+	 * so at first we silently check whether graph presents in the
+	 * device-tree node.
+	 */
+	if (!of_graph_is_present(np))
+		return -ENODEV;
+
 	remote = of_graph_get_remote_node(np, port, endpoint);
 	if (!remote)
 		return -ENODEV;
-- 
2.26.0