[RFC PATCH 1/1] of/irq: create interrupts-extended-2 property

[Mark Rutland]

> 
> Another, more invasive option would be extend the dts syntax and teach
> dtc to handle property appending. Then the soc dts could stay as it is,
> and the board dts could have something like:
> 
> 	/append-property/ interrupts = <&intc1 6 1>;
> 	/append-property/ interrupt-names = "board-specific-irq";
> 
> Both these options solve the issue at the source, are general to other
> properties, and allow more than one level of hierarchy (the proposed
> interrupts-extended-2 only allows one level).

I've just had a go at implementing the append-property mechanism above
in dtc, and it was far easier than I expected (patch below).

Does anyone have any issues with the /append-property/ idea?

Thanks,
Mark.

---->8----

>From 88be0036b6a966bd7506f58e3cb9ce9ea4c5ac48 Mon Sep 17 00:00:00 2001
From: Mark Rutland <mark.rutland at arm.com>
Date: Wed, 15 Jan 2014 15:43:51 +0000
Subject: [PATCH] dtc: add ability to append properties

When dealing with hierarchies of dtsi files, handling minute differences
between individual boards can become very painful. Adding a single
board-specific interrupt requires duplicating the entire interrupts
property, which requires duplication of common values. This makes bug
fixing painful and if not handled very carefully files diverge rapdily.

To ameliorate this, this patch adds the ability to append properties,
allowing board files to describe only the additional values required in
a property. This functionality also works with strings, so parallel
properties like interupts and interrupt-names stay in sync. Properties
may be appended multiple times, and deleting properties clears all
previous appended values.

To append a property, secondary definitions must be prefixed with
/append-property/. This is longer than a possible '+=' syntax, but makes
it far easier to spot when appending behaviour is requested, and so
hopefully will lead to fewer buggy dts files.

For example, if the following dts fragements are compiled together:

  / {
      interrupts = <0>, <1>;
      interrupt-names = "zero", "one";
  };

  / {
      /append-property/ interrupts = <2>, <3>;
      /append-property/ interrupt-names = "two", "three";
  };

They will result in a dtb equivalent to the following dts fragment:

  / {
      interrupts = <0>, <1>, <2>, <3>;
      interrupt-names = "zero", "one", "two", "three";
  };

Signed-off-by: Mark Rutland <mark.rutland at arm.com>
---
 dtc-lexer.l  |  7 +++++++
 dtc-parser.y |  5 +++++
 dtc.h        |  2 ++
 livetree.c   | 15 ++++++++++++++-
 4 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/dtc-lexer.l b/dtc-lexer.l
index 0cd7e67..7989abe 100644
--- a/dtc-lexer.l
+++ b/dtc-lexer.l
@@ -131,6 +131,13 @@ static bool pop_input_file(void);
 			return DT_DEL_PROP;
 		}
 
+<*>"/append-property/"	{
+			DPRINT("Keyword: /append-property/\n");
+			DPRINT("<PROPNODENAME>\n");
+			BEGIN(PROPNODENAME);
+			return DT_APPEND_PROP;
+		}
+
 <*>"/delete-node/"	{
 			DPRINT("Keyword: /delete-node/\n");
 			DPRINT("<PROPNODENAME>\n");
diff --git a/dtc-parser.y b/dtc-parser.y
index 4864631..a8409ed 100644
--- a/dtc-parser.y
+++ b/dtc-parser.y
@@ -63,6 +63,7 @@ static unsigned char eval_char_literal(const char *s);
 %token DT_LSHIFT DT_RSHIFT DT_LE DT_GE DT_EQ DT_NE DT_AND DT_OR
 %token DT_BITS
 %token DT_DEL_PROP
+%token DT_APPEND_PROP
 %token DT_DEL_NODE
 %token <propnodename> DT_PROPNODENAME
 %token <literal> DT_LITERAL
@@ -195,6 +196,10 @@ propdef:
 		{
 			$$ = build_property($1, empty_data);
 		}
+	| DT_APPEND_PROP DT_PROPNODENAME '=' propdata ';'
+		{
+			$$ = build_property_append($2, $4);
+		}
 	| DT_DEL_PROP DT_PROPNODENAME ';'
 		{
 			$$ = build_property_delete($2);
diff --git a/dtc.h b/dtc.h
index 20e4d56..8687530 100644
--- a/dtc.h
+++ b/dtc.h
@@ -133,6 +133,7 @@ struct label {
 };
 
 struct property {
+	bool appended;
 	bool deleted;
 	char *name;
 	struct data val;
@@ -186,6 +187,7 @@ void delete_labels(struct label **labels);
 
 struct property *build_property(char *name, struct data val);
 struct property *build_property_delete(char *name);
+struct property *build_property_append(char *name, struct data val);
 struct property *chain_property(struct property *first, struct property *list);
 struct property *reverse_properties(struct property *first);
 
diff --git a/livetree.c b/livetree.c
index b61465f..894e42b 100644
--- a/livetree.c
+++ b/livetree.c
@@ -74,6 +74,15 @@ struct property *build_property_delete(char *name)
 	return new;
 }
 
+struct property *build_property_append(char *name, struct data val)
+{
+	struct property *new = build_property(name, val);
+
+	new->appended = 1;
+
+	return new;
+}
+
 struct property *chain_property(struct property *first, struct property *list)
 {
 	assert(first->next == NULL);
@@ -167,7 +176,11 @@ struct node *merge_nodes(struct node *old_node, struct node *new_node)
 				for_each_label_withdel(new_prop->labels, l)
 					add_label(&old_prop->labels, l->label);
 
-				old_prop->val = new_prop->val;
+				if (new_prop->appended)
+					old_prop->val = data_merge(old_prop->val, new_prop->val);
+				else
+					old_prop->val = new_prop->val;
+
 				old_prop->deleted = 0;
 				free(new_prop);
 				new_prop = NULL;
-- 
1.8.1.1