On Thu, May 03, 2018 at 10:27:26PM +0200, Maxime Ripard wrote:
> A number of platforms have a need to reduce the number of DT nodes,
> mostly because of two similar constraints: the size of the DT blob, and
> the time it takes to parse it.
>
> As the DT is used in more and more SoCs, and by more projects, some
> constraints start to appear in bootloaders running from SRAM with an
> order of magnitude of 10kB. A typical DT is in the same order of
> magnitude, so any effort to reduce the blob size is welcome in such an
> environment.
>
> Some platforms also want to reach very fast boot time, and the time it
> takes to parse a typical DT starts to be noticeable.
>
> Both of these issues can be mitigated by reducing the number of nodes in
> the DT. The biggest provider of nodes is usually the pin controller and
> its subnodes, usually one for each valid pin configuration in a given
> SoC.
>
> Obviously, a single, fixed, set of these nodes will be used by a given
> board, so we can introduce a node property that will tell the DT
> compiler to drop the nodes when they are not referenced in the tree, and
> as such wouldn't be useful in the targetted system.
>
> Signed-off-by: Maxime Ripard <maxime.ripard@xxxxxxxxxxx>
Applied, thanks.
>
> ---
> Changes from v1:
> - Rename the property from delete-if-unreferenced to omit-if-no-ref
> - Change the various variables in the code to reflect this
> - Added support to set the property on a label instead of a full node
> - Also take into account the reference by path, and not only by
> phandle
> - Prune the unused nodes in a fixup pass, and not during the tree
> flattening that allows to have the same behaviour when having an
> output to a format other than dtb or asm
> - Rebased on current master
> ---
> checks.c | 13 +++++++++++++
> dtc-lexer.l | 7 +++++++
> dtc-parser.y | 17 +++++++++++++++++
> dtc.h | 4 ++++
> livetree.c | 14 ++++++++++++++
> 5 files changed, 55 insertions(+)
>
> diff --git a/checks.c b/checks.c
> index dca45aca73d7..a2cc1036c915 100644
> --- a/checks.c
> +++ b/checks.c
> @@ -584,6 +584,8 @@ static void fixup_phandle_references(struct check *c, struct dt_info *dti,
>
> phandle = get_node_phandle(dt, refnode);
> *((fdt32_t *)(prop->val.val + m->offset)) = cpu_to_fdt32(phandle);
> +
> + reference_node(refnode);
> }
> }
> }
> @@ -614,11 +616,21 @@ static void fixup_path_references(struct check *c, struct dt_info *dti,
> path = refnode->fullpath;
> prop->val = data_insert_at_marker(prop->val, m, path,
> strlen(path) + 1);
> +
> + reference_node(refnode);
> }
> }
> }
> ERROR(path_references, fixup_path_references, NULL, &duplicate_node_names);
>
> +static void fixup_omit_unused_nodes(struct check *c, struct dt_info *dti,
> + struct node *node)
> +{
> + if (node->omit_if_unused && !node->is_referenced)
> + delete_node(node);
> +}
> +ERROR(omit_unused_nodes, fixup_omit_unused_nodes, NULL, &phandle_references, &path_references);
> +
> /*
> * Semantic checks
> */
> @@ -1547,6 +1559,7 @@ static struct check *check_table[] = {
>
> &explicit_phandles,
> &phandle_references, &path_references,
> + &omit_unused_nodes,
>
> &address_cells_is_cell, &size_cells_is_cell, &interrupt_cells_is_cell,
> &device_type_is_string, &model_is_string, &status_is_string,
> diff --git a/dtc-lexer.l b/dtc-lexer.l
> index fd825ebba69c..615b7ec6588f 100644
> --- a/dtc-lexer.l
> +++ b/dtc-lexer.l
> @@ -153,6 +153,13 @@ static void PRINTF(1, 2) lexical_error(const char *fmt, ...);
> return DT_DEL_NODE;
> }
>
> +<*>"/omit-if-no-ref/" {
> + DPRINT("Keyword: /omit-if-no-ref/\n");
> + DPRINT("<PROPNODENAME>\n");
> + BEGIN(PROPNODENAME);
> + return DT_OMIT_NO_REF;
> + }
> +
> <*>{LABEL}: {
> DPRINT("Label: %s\n", yytext);
> yylval.labelref = xstrdup(yytext);
> diff --git a/dtc-parser.y b/dtc-parser.y
> index 25e92d64305c..011a5b25539a 100644
> --- a/dtc-parser.y
> +++ b/dtc-parser.y
> @@ -63,6 +63,7 @@ extern bool treesource_error;
> %token DT_BITS
> %token DT_DEL_PROP
> %token DT_DEL_NODE
> +%token DT_OMIT_NO_REF
> %token <propnodename> DT_PROPNODENAME
> %token <integer> DT_LITERAL
> %token <integer> DT_CHAR_LITERAL
> @@ -217,6 +218,18 @@ devicetree:
> ERROR(&@3, "Label or path %s not found", $3);
>
>
> + $$ = $1;
> + }
> + | devicetree DT_OMIT_NO_REF DT_REF ';'
> + {
> + struct node *target = get_node_by_ref($1, $3);
> +
> + if (target)
> + omit_node_if_unused(target);
> + else
> + ERROR(&@3, "Label or path %s not found", $3);
> +
> +
> $$ = $1;
> }
> ;
> @@ -523,6 +536,10 @@ subnode:
> {
> $$ = name_node(build_node_delete(), $2);
> }
> + | DT_OMIT_NO_REF subnode
> + {
> + $$ = omit_node_if_unused($2);
> + }
> | DT_LABEL subnode
> {
> add_label(&$2->labels, $1);
> diff --git a/dtc.h b/dtc.h
> index 3b18a42b866e..6d667701ab6a 100644
> --- a/dtc.h
> +++ b/dtc.h
> @@ -168,6 +168,8 @@ struct node {
>
> struct label *labels;
> const struct bus_type *bus;
> +
> + bool omit_if_unused, is_referenced;
> };
>
> #define for_each_label_withdel(l0, l) \
> @@ -202,6 +204,8 @@ struct property *reverse_properties(struct property *first);
> struct node *build_node(struct property *proplist, struct node *children);
> struct node *build_node_delete(void);
> struct node *name_node(struct node *node, char *name);
> +struct node *omit_node_if_unused(struct node *node);
> +struct node *reference_node(struct node *node);
> struct node *chain_node(struct node *first, struct node *list);
> struct node *merge_nodes(struct node *old_node, struct node *new_node);
> struct node *add_orphan_node(struct node *old_node, struct node *new_node, char *ref);
> diff --git a/livetree.c b/livetree.c
> index f691c9b5c935..6e4c367f54b3 100644
> --- a/livetree.c
> +++ b/livetree.c
> @@ -134,6 +134,20 @@ struct node *name_node(struct node *node, char *name)
> return node;
> }
>
> +struct node *omit_node_if_unused(struct node *node)
> +{
> + node->omit_if_unused = 1;
> +
> + return node;
> +}
> +
> +struct node *reference_node(struct node *node)
> +{
> + node->is_referenced = 1;
> +
> + return node;
> +}
> +
> struct node *merge_nodes(struct node *old_node, struct node *new_node)
> {
> struct property *new_prop, *old_prop;
--
David Gibson | 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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