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Message-ID: <aWiB3pDx4owt-70D@zatzit>
Date: Thu, 15 Jan 2026 16:57:50 +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 20/77] dtc: Add support for /export/ dts keyword
parsing
On Mon, Jan 12, 2026 at 03:19:10PM +0100, Herve Codina wrote:
> The /export/ dts keyword is the keyword used to define an exported
> symbol at a given node level.
>
> This keyword can be present in a node definition (after properties and
> before subnodes) to export a symbol. If several symbols need to be
> exported, several /export/ keywords are present.
>
> The syntax used is the following:
> /export/ name: reference;
>
> with:
> name: The name of the exported symbol
> reference: The reference of a node the symbol is pointing to.
>
> For instance:
> - Reference by label:
> /export/ foo: &foo1;
>
> The exported symbol foo references the node identified by
> the label foo1.
>
> - Reference by path:
> /export/ foo: &{/path/to/foo@...};
>
> The exported symbol foo references the node at /path/to/foo@....
>
> Add support for /export/ dts keyword.
>
> Signed-off-by: Herve Codina <herve.codina@...tlin.com>
> ---
> dtc-lexer.l | 6 ++++
> dtc-parser.y | 53 ++++++++++++++++++++++++++++++++++
> dtc.h | 8 ++++++
> livetree.c | 80 ++++++++++++++++++++++++++++++++++++++++++++++++++++
> 4 files changed, 147 insertions(+)
>
> diff --git a/dtc-lexer.l b/dtc-lexer.l
> index a4a8e0b..90fe70e 100644
> --- a/dtc-lexer.l
> +++ b/dtc-lexer.l
> @@ -149,6 +149,12 @@ static void PRINTF(1, 2) lexical_error(const char *fmt, ...);
> return DT_OMIT_NO_REF;
> }
>
> +<*>"/export/" {
> + DPRINT("Keyword: /export/\n");
> + BEGIN_DEFAULT();
> + return DT_EXPORT;
> + }
> +
> <*>{LABEL}: {
> DPRINT("Label: %s\n", yytext);
> yylval.labelref = xstrdup(yytext);
> diff --git a/dtc-parser.y b/dtc-parser.y
> index 9c93673..a0d0aef 100644
> --- a/dtc-parser.y
> +++ b/dtc-parser.y
> @@ -46,6 +46,8 @@ static bool is_ref_relative(const char *ref)
> struct property *proplist;
> struct node *node;
> struct node *nodelist;
> + struct symbol *symbol;
> + struct symbol *exportlist;
> struct reserve_info *re;
> uint64_t integer;
> unsigned int flags;
> @@ -60,6 +62,7 @@ static bool is_ref_relative(const char *ref)
> %token DT_DEL_PROP
> %token DT_DEL_NODE
> %token DT_OMIT_NO_REF
> +%token DT_EXPORT
> %token <propnodename> DT_PROPNODENAME
> %token <integer> DT_LITERAL
> %token <integer> DT_CHAR_LITERAL
> @@ -80,6 +83,8 @@ static bool is_ref_relative(const char *ref)
> %type <data> bytestring
> %type <prop> propdef
> %type <proplist> proplist
> +%type <symbol> exportdef
> +%type <exportlist> exportlist
> %type <labelref> dt_ref
>
> %type <node> devicetree
> @@ -276,6 +281,49 @@ nodedef:
> {
> $$ = build_node(NULL, $2, NULL, &@$);
> }
> + | '{' proplist exportlist subnodes '}' ';'
> + {
> + /*
> + * exportlist is created with chain_symbol() and so it
> + * is created in reverse order. Reverse it now to have
> + * it in correct order
> + */
> + $$ = build_node($2, $4, reverse_symbol($3), &@$);
> + }
> + | '{' exportlist subnodes '}' ';'
> + {
> + /*
> + * exportlist is created with chain_symbol() and so it
> + * is created in reverse order. Reverse it now to have
> + * it in correct order
> + */
> + $$ = build_node(NULL, $3, reverse_symbol($2), &@$);
> + }
> + ;
> +
> +exportlist:
> + exportdef
> + {
> + $$ = chain_symbol($1, NULL);
> + }
> + | exportlist exportdef
> + {
> + $$ = chain_symbol($2, $1);
> + }
> + | exportlist propdef
> + {
> + ERROR(&@2, "Properties must precede exports");
> + YYERROR;
> + }
> + ;
> +
> +exportdef:
> + DT_EXPORT DT_LABEL dt_ref ';'
> + {
> + $$ = build_exportsym($2, $3, 0, &@$);
> + free($2);
> + free($3);
I mostly don't bother with free()s in dtc, on the grounds that it's
generally a short-lived process - essentially using the process
context as a crude pool allocator.
> + }
> ;
>
> proplist:
> @@ -576,6 +624,11 @@ subnodes:
> ERROR(&@2, "Properties must precede subnodes");
> YYERROR;
> }
> + | subnode exportdef
> + {
> + ERROR(&@2, "Exports must precede subnodes");
> + YYERROR;
> + }
> ;
>
> subnode:
> diff --git a/dtc.h b/dtc.h
> index 6508694..0bf5ba5 100644
> --- a/dtc.h
> +++ b/dtc.h
> @@ -273,6 +273,9 @@ struct node {
> for_each_child_withdel(n, c) \
> if (!(c)->deleted)
>
> +#define for_each_symbol(s0, s) \
> + for ((s) = (s0); (s); (s) = (s)->next)
> +
> void add_label(struct label **labels, char *label);
> void delete_labels(struct label **labels);
>
> @@ -282,6 +285,11 @@ struct property *build_property_delete(const char *name);
> struct property *chain_property(struct property *first, struct property *list);
> struct property *reverse_properties(struct property *first);
>
> +struct symbol *build_exportsym(const char *name, const char *ref, cell_t phandle,
> + struct srcpos *srcpos);
> +struct symbol *chain_symbol(struct symbol *first, struct symbol *list);
> +struct symbol *reverse_symbol(struct symbol *list);
> +
> struct node *build_node(struct property *proplist, struct node *children,
> struct symbol *exportsymlist, struct srcpos *srcpos);
> struct node *build_node_delete(struct srcpos *srcpos);
> diff --git a/livetree.c b/livetree.c
> index 0050492..4458437 100644
> --- a/livetree.c
> +++ b/livetree.c
> @@ -36,6 +36,57 @@ void delete_labels(struct label **labels)
> label->deleted = 1;
> }
>
> +struct symbol *build_exportsym(const char *name, const char *ref, cell_t phandle,
> + struct srcpos *srcpos)
> +{
> + struct symbol *new = xmalloc(sizeof(*new));
> +
> + memset(new, 0, sizeof(*new));
> +
> + new->name = xstrdup(name);
> + new->ref = ref ? xstrdup(ref) : NULL;
> + new->phandle = phandle;
> + new->srcpos = srcpos_copy(srcpos);
> +
> + return new;
> +}
> +
> +struct symbol *chain_symbol(struct symbol *first, struct symbol *list)
> +{
> + assert(first->next == NULL);
> +
> + first->next = list;
> + return first;
> +}
> +
> +struct symbol *reverse_symbol(struct symbol *list)
> +{
> + struct symbol *p = list;
> + struct symbol *head = NULL;
> + struct symbol *next;
> +
> + while (p) {
> + next = p->next;
> + p->next = head;
> + head = p;
> + p = next;
> + }
> + return head;
> +}
> +
> +static void add_symbol(struct symbol **list, struct symbol *new)
> +{
> + struct symbol **s;
> +
> + new->next = NULL;
> +
> + s = list;
> + while (*s)
> + s = &((*s)->next);
> +
> + *s = new;
> +}
> +
> struct property *build_property(const char *name, struct data val,
> struct srcpos *srcpos)
> {
> @@ -144,6 +195,7 @@ struct node *merge_nodes(struct node *old_node, struct node *new_node)
> {
> struct property *new_prop, *old_prop;
> struct node *new_child, *old_child;
> + struct symbol *new_sym, *old_sym;
> struct label *l;
>
> old_node->deleted = 0;
> @@ -217,6 +269,34 @@ struct node *merge_nodes(struct node *old_node, struct node *new_node)
> add_child(old_node, new_child);
> }
>
> + /* Merge exported symbols. If there is a collision, keep the new one */
> + while (new_node->exportsymlist) {
> + /* Pop the symbol off the list */
> + new_sym = new_node->exportsymlist;
> + new_node->exportsymlist = new_sym->next;
> + new_sym->next = NULL;
> +
> + /* Look for a collision, set new value if there is */
> + for_each_symbol(old_node->exportsymlist, old_sym) {
> + if (streq(old_sym->name, new_sym->name)) {
> + old_sym->is_local = new_sym->is_local;
> + free(old_sym->ref);
> + old_sym->ref = new_sym->ref;
> + old_sym->phandle = new_sym->phandle;
> + old_sym->fullpath = new_sym->fullpath;
> + srcpos_free(old_sym->srcpos);
> + old_sym->srcpos = new_sym->srcpos;
> + free(new_sym);
> + new_sym = NULL;
> + break;
> + }
> + }
> +
> + /* if no collision occurred, add symbol to the old node list. */
> + if (new_sym)
> + add_symbol(&old_node->exportsymlist, new_sym);
> + }
> +
> old_node->srcpos = srcpos_extend(old_node->srcpos, new_node->srcpos);
>
> /* The new node contents are now merged into the old node. Free
> --
> 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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