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Message-ID: <1393428297.3248.92.camel@paszta.hi.pengutronix.de>
Date: Wed, 26 Feb 2014 16:24:57 +0100
From: Philipp Zabel <p.zabel@...gutronix.de>
To: Grant Likely <grant.likely@...aro.org>
Cc: Russell King - ARM Linux <linux@....linux.org.uk>,
Mauro Carvalho Chehab <m.chehab@...sung.com>,
Rob Herring <robh+dt@...nel.org>,
Sylwester Nawrocki <s.nawrocki@...sung.com>,
Laurent Pinchart <laurent.pinchart@...asonboard.com>,
Tomi Valkeinen <tomi.valkeinen@...com>,
Kyungmin Park <kyungmin.park@...sung.com>,
linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
devicetree@...r.kernel.org,
Guennadi Liakhovetski <g.liakhovetski@....de>,
Philipp Zabel <philipp.zabel@...il.com>
Subject: Re: [PATCH v4 1/3] [media] of: move graph helpers from
drivers/media/v4l2-core to drivers/of
Hi Grant,
Am Mittwoch, den 26.02.2014, 11:37 +0000 schrieb Grant Likely:
[...]
> > drivers/media/v4l2-core/v4l2-of.c | 117 ----------------------
> > drivers/of/Makefile | 1 +
> > drivers/of/of_graph.c | 134 ++++++++++++++++++++++++++
>
> Nah. Just put it into drivers/of/base.c. This isn't a separate subsystem
> and the functions are pretty basic.
Ok.
[...]
> > +struct device_node *of_graph_get_next_endpoint(const struct device_node *parent,
> > + struct device_node *prev)
> > +{
> > + struct device_node *endpoint;
> > + struct device_node *port = NULL;
> > +
> > + if (!parent)
> > + return NULL;
> > +
> > + if (!prev) {
> > + struct device_node *node;
> > + /*
> > + * It's the first call, we have to find a port subnode
> > + * within this node or within an optional 'ports' node.
> > + */
> > + node = of_get_child_by_name(parent, "ports");
> > + if (node)
> > + parent = node;
> > +
> > + port = of_get_child_by_name(parent, "port");
>
> If you've got a "ports" node, then I would expect every single child to
> be a port. Should not need the _by_name variant.
The 'ports' node is optional. It is only needed if the parent node has
its own #address-cells and #size-cells properties. If the ports are
direct children of the device node, there might be other nodes than
ports:
device {
#address-cells = <1>;
#size-cells = <0>;
port@0 {
endpoint { ... };
};
port@1 {
endpoint { ... };
};
some-other-child { ... };
};
device {
#address-cells = <x>;
#size-cells = <y>;
ports {
#address-cells = <1>;
#size-cells = <0>;
port@0 {
endpoint { ... };
};
port@1 {
endpoint { ... };
};
};
some-other-child { ... };
};
The helper should find the two endpoints in both cases.
Tomi suggests an even more compact form for devices with just one port:
device {
endpoint { ... };
some-other-child { ... };
};
> It seems that this function is merely a helper to get all grandchildren
> of a node (with some very minor constraints). That could be generalized
> and simplified. If the function takes the "ports" node as an argument
> instead of the parent, then there is a greater likelyhood that other
> code can make use of it...
>
> Thinking further. I think the semantics of this whole feature basically
> boil down to this:
>
> #define for_each_grandchild_of_node(parent, child, grandchild) \
> for_each_child_of_node(parent, child) \
> for_each_child_of_node(child, grandchild)
>
> Correct? Or in this specific case:
>
> parent = of_get_child_by_name(np, "ports")
> for_each_grandchild_of_node(parent, child, grandchild) {
> ...
> }
Hmm, that would indeed be a bit more generic, but it doesn't handle the
optional 'ports' subnode and doesn't allow for other child nodes in the
device node.
> Finally, looking at the actual patch, is any of this actually needed.
> All of the users updated by this patch only ever handle a single
> endpoint. Have I read it correctly? Are there any users supporting
> multiple endpoints?
Yes, mainline currently only contains simple cases. I have posted i.MX6
patches that use this scheme for the output path:
http://www.spinics.net/lists/arm-kernel/msg310817.html
http://www.spinics.net/lists/arm-kernel/msg310821.html
> > +
> > + if (port) {
> > + /* Found a port, get an endpoint. */
> > + endpoint = of_get_next_child(port, NULL);
> > + of_node_put(port);
> > + } else {
> > + endpoint = NULL;
> > + }
> > +
> > + if (!endpoint)
> > + pr_err("%s(): no endpoint nodes specified for %s\n",
> > + __func__, parent->full_name);
> > + of_node_put(node);
>
> If you 'return endpoint' here, then the else block can go down a level.
Note that this patch is a straight move of existing code.
I can follow up with code beautification and ...
> > + } else {
> > + port = of_get_parent(prev);
> > + if (!port)
> > + /* Hm, has someone given us the root node ?... */
> > + return NULL;
>
> WARN_ONCE(). That's a very definite coding failure if that happens.
... with a fix for this.
> > +
> > + /* Avoid dropping prev node refcount to 0. */
> > + of_node_get(prev);
> > + endpoint = of_get_next_child(port, prev);
> > + if (endpoint) {
> > + of_node_put(port);
> > + return endpoint;
> > + }
> > +
> > + /* No more endpoints under this port, try the next one. */
> > + do {
> > + port = of_get_next_child(parent, port);
> > + if (!port)
> > + return NULL;
> > + } while (of_node_cmp(port->name, "port"));
> > +
> > + /* Pick up the first endpoint in this port. */
> > + endpoint = of_get_next_child(port, NULL);
> > + of_node_put(port);
> > + }
> > +
> > + return endpoint;
> > +}
> > +EXPORT_SYMBOL(of_graph_get_next_endpoint);
> > +
> > +/**
> > + * of_graph_get_remote_port_parent() - get remote port's parent node
> > + * @node: pointer to a local endpoint device_node
> > + *
> > + * Return: Remote device node associated with remote endpoint node linked
> > + * to @node. Use of_node_put() on it when done.
> > + */
> > +struct device_node *of_graph_get_remote_port_parent(
> > + const struct device_node *node)
> > +{
> > + struct device_node *np;
> > + unsigned int depth;
> > +
> > + /* Get remote endpoint node. */
> > + np = of_parse_phandle(node, "remote-endpoint", 0);
> > +
> > + /* Walk 3 levels up only if there is 'ports' node. */
>
> This needs a some explaining. My reading of the binding pattern is that
> it will always be a fixed number of levels. Why is this test fuzzy?
[...]
See above. The ports subnode level is optional. In most cases, the port
nodes will be direct children of the device node.
Walking up 3 levels from the endpoint node will return the device if
there was a ports node. If there is no ports node, we only have to walk
up two levels.
regards
Philipp
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