Re: [PATCH 02/13] dtc: Add a list for the top-level fragments of a dts file

[Herve Codina <herve.codina@bootlin.com>]

On Sun,  1 Nov 2026 09:36:56 -0700
Simon Glass <sjg@chromium.org> wrote:

> A dts file is made up of top-level fragments: the root node, later
> definitions of a node by label or path, and /delete-node/ or
> /omit-if-no-ref/ with a reference. We would like to deal with each
> fragment on its own before it is merged, for example to apply deletes
> consistently or to run some checks on each one, but that requires
> keeping the fragments apart. At present the parser merges each one into
> the tree as soon as it is parsed.
> 
> Add a struct fragment to hold one of these, functions to build one, to
> append it to a list and to free it, and a list of them in struct dt_info
> 
> These are not used yet.
> 
> Assisted-by: Claude:claude-opus-5-5
> Signed-off-by: Simon Glass <sjg@chromium.org>
> ---
> 
>  dtc.h      | 47 ++++++++++++++++++++++++++++++++++++++++++
>  livetree.c | 60 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 107 insertions(+)
> 
> diff --git a/dtc.h b/dtc.h
> index 473552e..c0d8e8f 100644
> --- a/dtc.h
> +++ b/dtc.h
> @@ -322,12 +322,59 @@ struct reserve_info *chain_reserve_entry(struct reserve_info *first,
>  struct reserve_info *add_reserve_entry(struct reserve_info *list,
>  				       struct reserve_info *new);
>  
> +/*
> + * A fragment is one top-level part of a dts file, after the header and any
> + * memory reservations: the root node, a later definition of a node which
> + * refers to it by label or path, or a /delete-node/ or /omit-if-no-ref/ with
> + * a reference. Fragments are kept apart until they are merged into a single
> + * tree.
> + *
> + * This is not the same as an overlay fragment (a fragment@N node), although
> + * in a plugin a fragment may become one when it is merged.
> + */
> +
> +enum fragment_type {
> +	FRAGMENT_ROOT,		/* / { ... }; */
> +	FRAGMENT_REF,		/* [label:] &ref { ... }; */
> +	FRAGMENT_DELETE_NODE,	/* /delete-node/ &ref; */
> +	FRAGMENT_OMIT_IF_NO_REF, /* /omit-if-no-ref/ &ref; */
> +};
> +
> +/*
> + * Which fields are used depends on the type:
> + *
> + *   FRAGMENT_ROOT            node
> + *   FRAGMENT_REF             ref, path_ref, ref_srcpos and node, plus label
> + *                            and label_srcpos if there is a label
> + *   FRAGMENT_DELETE_NODE     ref, path_ref and ref_srcpos
> + *   FRAGMENT_OMIT_IF_NO_REF  ref, path_ref and ref_srcpos
> + *
> + * Unused fields are NULL or false.
> + */
> +struct fragment {
> +	enum fragment_type type;
> +	char *ref;			/* label or path referred to */
> +	bool path_ref;			/* ref is a path, i.e. &{...} */
> +	struct srcpos *ref_srcpos;	/* position of ref */
> +	char *label;			/* label to add to the target */
> +	struct srcpos *label_srcpos;	/* position of label */
> +	struct node *node;		/* the node definition */
> +
> +	struct fragment *next;		/* NULL at the end of the list */
> +};
> +
> +struct fragment *build_fragment(enum fragment_type type, struct node *node);
> +struct fragment *build_fragment_ref(char *ref, bool path_ref,
> +				    struct srcpos *srcpos);
> +struct fragment *append_fragment(struct fragment *list, struct fragment *new);
> +void free_fragment(struct fragment *f);
>  
>  struct dt_info {
>  	unsigned int dtsflags;
>  	struct reserve_info *reservelist;
>  	uint32_t boot_cpuid_phys;
>  	struct node *dt;		/* the device tree */
> +	struct fragment *fragments;	/* not yet merged into dt */

Why to we need the fragment list in struct dt_info ?

This list is a temporary list built_dt_info() could have the list as parameter and
handle it leading to the struct node *dt fully updated.

Other function using the struct dt_info should never see the temporary fragment 
list and so, IMHO, there is no reason to store it in the struct dt_info.

Best regards,
Hervé