Re: [RFC PATCH 19/77] dtc: Introduce export symbols

[David Gibson <david@gibson.dropbear.id.au>]

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On Mon, Jan 12, 2026 at 03:19:09PM +0100, Herve Codina wrote:
> Export symbols allow to define a list of symbols exported at a given
> node level. Those exported symbols can be used by an addon when the
> addon is applied on the node exporting the symbols.

This seems to imply an addon always applies at a single node location.
I'm not sure that's a good design choice, since I don't see how it
covers the case of something that connects to several connectors.

> In order to perform
> its symbol resolution. Any unresolved phandle value will be resolved
> using those exported symbols.
> 
> The feature is similar to __symbols__ involved with overlay but while
> all symbols are visible with __symbols__, only specific symbols
> (exported symbols) are visible with export symbols.

This paragraph doesn't make sense to me.  What's a "symbol" if it's
not something in __symbols__ or export symbols?

> Also an exported symbol has a specific name and this name has to
> used for symbol resolution. Having this specific name allows to:
> 
>   - Have several nodes providing the same exported symbols
>     name but each of them pointing to different nodes.

That's not a property of having a specific name, that's a property of
being local to a node.

>     Without looking at the detail of the syntax, node-a and node-b
>     export the same symbol foo but pointing to different node.
>       node-a {
>         /* export foo -> /path/foo1 */
>       };
>       node-b {
>         /* export foo -> /path/foo2 */
>       };
> 
>     This allow to have the exact same addon referencing 'foo' applied
>     either on node-a or node-b.
> 
>   - Have several board describing a well defined node even if resources
>     needed for exported symbols are not the same.
> 
>     On board A, the 'ctrl' exported symbols points to some ctrl device
>     available on the SoC:
>       node {
>         /* export 'ctrl' -> /soc/ctrl@1000
>       };
> 
>     On board B, the ctrl device used is on a i2c bus
>       node {
>         /* export 'ctrl' -> /soc/i2c@5000/ctrl@10
>       };
> 
>     The addon can be used on board A and board B without any
>     modification. It uses 'ctrl' exported by the node the it is applied
>     to.
> 
> Introduce the 'symbol' internal data structure and the export symbol
> list related to a node.
> 
> No functional change yet but preparation for the future support
> for export symbol parsing.
> 
> Signed-off-by: Herve Codina <herve.codina@bootlin.com>
> ---
>  dtc-parser.y |  6 +++---
>  dtc.h        | 13 ++++++++++++-
>  flattree.c   |  2 +-
>  fstree.c     |  2 +-
>  livetree.c   |  7 ++++---
>  5 files changed, 21 insertions(+), 9 deletions(-)
> 
> diff --git a/dtc-parser.y b/dtc-parser.y
> index 2e152b0..9c93673 100644
> --- a/dtc-parser.y
> +++ b/dtc-parser.y
> @@ -183,7 +183,7 @@ devicetree:
>  			else if (is_ref_relative($1))
>  				ERROR(&@2, "Label-relative reference %s not supported in plugin", $1);
>  			$$ = add_orphan_node(
> -					name_node(build_node(NULL, NULL, NULL),
> +					name_node(build_node(NULL, NULL, NULL, NULL),
>  						  ""),
>  					$2, $1);
>  		}
> @@ -270,11 +270,11 @@ devicetree:
>  nodedef:
>  	  '{' proplist subnodes '}' ';'
>  		{
> -			$$ = build_node($2, $3, &@$);
> +			$$ = build_node($2, $3, NULL, &@$);
>  		}
>  	| '{' subnodes '}' ';'
>  		{
> -			$$ = build_node(NULL, $2, &@$);
> +			$$ = build_node(NULL, $2, NULL, &@$);
>  		}
>  	;
>  
> diff --git a/dtc.h b/dtc.h
> index c0fffd2..6508694 100644
> --- a/dtc.h
> +++ b/dtc.h
> @@ -204,6 +204,16 @@ struct label {
>  	struct label *next;
>  };
>  
> +struct symbol {
> +	bool is_local;
> +	char *name;
> +	char *ref;
> +	cell_t phandle;
> +	char *fullpath;
> +	struct symbol *next;
> +	struct srcpos *srcpos;
> +};
> +
>  struct bus_type {
>  	const char *name;
>  };
> @@ -224,6 +234,7 @@ struct node {
>  	char *name;
>  	struct property *proplist;
>  	struct node *children;
> +	struct symbol *exportsymlist;
>  
>  	struct node *parent;
>  	struct node *next_sibling;
> @@ -272,7 +283,7 @@ struct property *chain_property(struct property *first, struct property *list);
>  struct property *reverse_properties(struct property *first);
>  
>  struct node *build_node(struct property *proplist, struct node *children,
> -			struct srcpos *srcpos);
> +			struct symbol *exportsymlist, struct srcpos *srcpos);
>  struct node *build_node_delete(struct srcpos *srcpos);
>  struct node *name_node(struct node *node, const char *name);
>  struct node *omit_node_if_unused(struct node *node);
> diff --git a/flattree.c b/flattree.c
> index bedb286..36b795d 100644
> --- a/flattree.c
> +++ b/flattree.c
> @@ -809,7 +809,7 @@ static struct node *unflatten_tree(struct inbuf *dtbuf,
>  	uint32_t offset;
>  	const char *str;
>  
> -	node = build_node(NULL, NULL, NULL);
> +	node = build_node(NULL, NULL, NULL, NULL);
>  
>  	flatname = flat_read_string(dtbuf);
>  
> diff --git a/fstree.c b/fstree.c
> index 0f9a534..445ae53 100644
> --- a/fstree.c
> +++ b/fstree.c
> @@ -19,7 +19,7 @@ static struct node *read_fstree(const char *dirname)
>  	if (!d)
>  		die("Couldn't opendir() \"%s\": %s\n", dirname, strerror(errno));
>  
> -	tree = build_node(NULL, NULL, NULL);
> +	tree = build_node(NULL, NULL, NULL, NULL);
>  
>  	while ((de = readdir(d)) != NULL) {
>  		char *tmpname;
> diff --git a/livetree.c b/livetree.c
> index 2a0a7ed..0050492 100644
> --- a/livetree.c
> +++ b/livetree.c
> @@ -86,7 +86,7 @@ struct property *reverse_properties(struct property *first)
>  }
>  
>  struct node *build_node(struct property *proplist, struct node *children,
> -			struct srcpos *srcpos)
> +			struct symbol *exportsymlist, struct srcpos *srcpos)
>  {
>  	struct node *new = xmalloc(sizeof(*new));
>  	struct node *child;
> @@ -95,6 +95,7 @@ struct node *build_node(struct property *proplist, struct node *children,
>  
>  	new->proplist = reverse_properties(proplist);
>  	new->children = children;
> +	new->exportsymlist = exportsymlist;
>  	new->srcpos = srcpos_copy(srcpos);
>  
>  	for_each_child(new, child) {
> @@ -248,7 +249,7 @@ struct node * add_orphan_node(struct node *dt, struct node *new_node, char *ref)
>  	xasprintf(&name, "fragment@%u",
>  			next_orphan_fragment++);
>  	name_node(new_node, "__overlay__");
> -	node = build_node(p, new_node, NULL);
> +	node = build_node(p, new_node, NULL, NULL);
>  	name_node(node, name);
>  	free(name);
>  
> @@ -892,7 +893,7 @@ static struct node *build_and_name_child_node(struct node *parent, const char *n
>  {
>  	struct node *node;
>  
> -	node = build_node(NULL, NULL, NULL);
> +	node = build_node(NULL, NULL, NULL, NULL);
>  	name_node(node, name);
>  	add_child(parent, node);
>  
> -- 
> 2.52.0
> 
> 

-- 
David Gibson (he or they)	| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you, not the other way
				| around.
http://www.ozlabs.org/~dgibson

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