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Message-ID: <aWiAmjfMiKpC4sdp@zatzit>
Date: Thu, 15 Jan 2026 16:52:26 +1100
From: David Gibson <david@...son.dropbear.id.au>
To: Herve Codina <herve.codina@...tlin.com>
Cc: Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk@...nel.org>,
Conor Dooley <conor+dt@...nel.org>,
Ayush Singh <ayush@...gleboard.org>,
Geert Uytterhoeven <geert@...ux-m68k.org>,
devicetree-compiler@...r.kernel.org, devicetree@...r.kernel.org,
linux-kernel@...r.kernel.org, devicetree-spec@...r.kernel.org,
Hui Pu <hui.pu@...ealthcare.com>,
Ian Ray <ian.ray@...ealthcare.com>,
Luca Ceresoli <luca.ceresoli@...tlin.com>,
Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Subject: Re: [RFC PATCH 19/77] dtc: Introduce export symbols
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@...0
> };
>
> On board B, the ctrl device used is on a i2c bus
> node {
> /* export 'ctrl' -> /soc/i2c@...0/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@...tlin.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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