Re: [PATCH v2 06/12] software_node: Add support for fwnode_graph*() family of functions

[Daniel Scally]

Hi Laurent - thanks for comments as always

On 18/12/2020 16:22, Laurent Pinchart wrote:
> Hi Daniel,
> 
> Thank you for the patch.
> 
> On Thu, Dec 17, 2020 at 11:43:31PM +0000, Daniel Scally wrote:
>> From: Heikki Krogerus <heikki.krogerus@xxxxxxxxxxxxxxx>
>>
>> This implements the remaining .graph_* callbacks in the
>> fwnode operations structure for the software nodes. That makes
>> the fwnode_graph*() functions available in the drivers also
>> when software nodes are used.
>>
>> The implementation tries to mimic the "OF graph" as much as
>> possible, but there is no support for the "reg" device
>> property. The ports will need to have the index in their
>> name which starts with "port@" (for example "port@0", "port@1",
>> ...) and endpoints will use the index of the software node
>> that is given to them during creation. The port nodes can
>> also be grouped under a specially named "ports" subnode,
>> just like in DT, if necessary.
>>
>> The remote-endpoints are reference properties under the
>> endpoint nodes that are named "remote-endpoint".
>>
>> Signed-off-by: Heikki Krogerus <heikki.krogerus@xxxxxxxxxxxxxxx>
>> Co-developed-by: Daniel Scally <djrscally@xxxxxxxxx>
>> Signed-off-by: Daniel Scally <djrscally@xxxxxxxxx>
>> ---
>> Changes in v2:
>>
>> 	- Changed commit to specify port name prefix as port@
>> 	- Accounted for that rename in *parse_endpoint()
>>
>>  drivers/base/swnode.c | 110 +++++++++++++++++++++++++++++++++++++++++-
>>  1 file changed, 109 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/base/swnode.c b/drivers/base/swnode.c
>> index 2b90d380039b..0d14d5ebe441 100644
>> --- a/drivers/base/swnode.c
>> +++ b/drivers/base/swnode.c
>> @@ -540,6 +540,110 @@ software_node_get_reference_args(const struct fwnode_handle *fwnode,
>>  	return 0;
>>  }
>>  
>> +static struct fwnode_handle *
>> +swnode_graph_find_next_port(const struct fwnode_handle *parent,
>> +			    struct fwnode_handle *port)
>> +{
>> +	struct fwnode_handle *old = port;
>> +
>> +	while ((port = software_node_get_next_child(parent, old))) {
>> +		if (!strncmp(to_swnode(port)->node->name, "port", 4))
> 
> Maybe we'll need to limit this to matching on "port" or "port@[0-9]+" to
> avoid false positives, but that can be done later, if needed.

Hmm yeah I guess that's a danger - ok, I'll stick it on the list.


>> +			return port;
>> +		old = port;
>> +	}
>> +
>> +	return NULL;
>> +}
>> +
>> +static struct fwnode_handle *
>> +software_node_graph_get_next_endpoint(const struct fwnode_handle *fwnode,
>> +				      struct fwnode_handle *endpoint)
>> +{
>> +	struct swnode *swnode = to_swnode(fwnode);
>> +	struct fwnode_handle *old = endpoint;
>> +	struct fwnode_handle *parent;
>> +	struct fwnode_handle *port;
>> +
>> +	if (!swnode)
>> +		return NULL;
>> +
>> +	if (endpoint) {
>> +		port = software_node_get_parent(endpoint);
> 
> Here the reference count to port is incremented.
> 
>> +		parent = software_node_get_parent(port);
>> +	} else {
>> +		parent = software_node_get_named_child_node(fwnode, "ports");
>> +		if (!parent)
>> +			parent = software_node_get(&swnode->fwnode);
>> +
>> +		port = swnode_graph_find_next_port(parent, NULL);
> 
> But here it isn't, software_node_get_next_child() doesn't deal with
> reference counts.

Not as in the kernel right now, but after patch one of this series, it does:

[PATCH v2 01/12] software_node: Fix refcounts in
software_node_get_next_child()

I'm not sure that one linked to the thread correctly, but it's here if
you haven't seen it:

https://lore.kernel.org/linux-media/20201217234337.1983732-2-djrscally@xxxxxxxxx/T/#u

The tl;dr of the change is that it will now get() the next node (if
found) and **always** put() if one is passed.


>> +	}
>> +
>> +	for (; port; port = swnode_graph_find_next_port(parent, port)) {
> 
> So if the loop terminates normally, the reference acquired in the first
> branch of the if will be leaked.
> 
>> +		endpoint = software_node_get_next_child(port, old);
>> +		if (endpoint) {
>> +			fwnode_handle_put(port);
> 
> While in this case the reference not acquired in the second branch of
> the if will be released incorrectly.
> 
> I think it's software_node_get_next_child() that needs to be fixed if
> I'm not mistaken.

I think that's all handled in software_node_get_next_child() as amended
by 01/12. The net effect of get_next_endpoint() should be one refcount
increased for any endpoint returned, and 0 change to parent and any ports.


>> +			break;
>> +		}
>> +
>> +		/* No more endpoints for that port, so stop passing old */
>> +		old = NULL;
> 
> I wonder if you could drop the 'old' variable and use 'enpoint' in the
> call to software_node_get_next_child(). You could then drop these two
> lines.

That won't work, because endpoint would at that point not be a child of
the port we're passing, and the function relies on it being one:

	if (!p || list_empty(&p->children) ||
	    (c && list_is_last(&c->entry, &p->children))) {
		fwnode_handle_put(child);
		return NULL;
	}

>> +	}
>> +
>> +	fwnode_handle_put(parent);
>> +
>> +	return endpoint;
>> +}
>> +
>> +static struct fwnode_handle *
>> +software_node_graph_get_remote_endpoint(const struct fwnode_handle *fwnode)
>> +{
>> +	struct swnode *swnode = to_swnode(fwnode);
>> +	const struct software_node_ref_args *ref;
>> +	const struct property_entry *prop;
>> +
>> +	if (!swnode)
>> +		return NULL;
>> +
>> +	prop = property_entry_get(swnode->node->properties, "remote-endpoint");
>> +	if (!prop || prop->type != DEV_PROP_REF || prop->is_inline)
>> +		return NULL;
>> +
>> +	ref = prop->pointer;
>> +
>> +	return software_node_get(software_node_fwnode(ref[0].node));
>> +}
>> +
>> +static struct fwnode_handle *
>> +software_node_graph_get_port_parent(struct fwnode_handle *fwnode)
>> +{
>> +	struct swnode *swnode = to_swnode(fwnode);
>> +	struct fwnode_handle *parent;
>> +
>> +	if (!strcmp(swnode->parent->node->name, "ports"))
>> +		parent = &swnode->parent->parent->fwnode;
>> +	else
>> +		parent = &swnode->parent->fwnode;
>> +
>> +	return software_node_get(parent);
>> +}
>> +
>> +static int
>> +software_node_graph_parse_endpoint(const struct fwnode_handle *fwnode,
>> +				   struct fwnode_endpoint *endpoint)
>> +{
>> +	struct swnode *swnode = to_swnode(fwnode);
>> +	int ret;
>> +
>> +	ret = kstrtou32(swnode->parent->node->name + 5, 10, &endpoint->port);
>> +	if (ret)
>> +		return ret;
>> +
>> +	endpoint->id = swnode->id;
>> +	endpoint->local_fwnode = fwnode;
>> +
>> +	return 0;
>> +}
>> +
>>  static const struct fwnode_operations software_node_ops = {
>>  	.get = software_node_get,
>>  	.put = software_node_put,
>> @@ -551,7 +655,11 @@ static const struct fwnode_operations software_node_ops = {
>>  	.get_parent = software_node_get_parent,
>>  	.get_next_child_node = software_node_get_next_child,
>>  	.get_named_child_node = software_node_get_named_child_node,
>> -	.get_reference_args = software_node_get_reference_args
>> +	.get_reference_args = software_node_get_reference_args,
>> +	.graph_get_next_endpoint = software_node_graph_get_next_endpoint,
>> +	.graph_get_remote_endpoint = software_node_graph_get_remote_endpoint,
>> +	.graph_get_port_parent = software_node_graph_get_port_parent,
>> +	.graph_parse_endpoint = software_node_graph_parse_endpoint,
>>  };
>>  
>>  /* -------------------------------------------------------------------------- */
>