acpigen: Support writing a package

A package collects together several elements. Add an easy way of writing
a package header and updating its length later.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Wolfgang Wallner <wolfgang.wallner@br-automation.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>

include/acpi/acpigen.h

@@ -17,6 +17,11 @@ struct acpi_ctx;
 /* Top 4 bits of the value used to indicate a three-byte length value */
 #define ACPI_PKG_LEN_3_BYTES	0x80
 
+/* ACPI Op/Prefix codes */
+enum {
+	PACKAGE_OP		= 0x12,
+};
+
 /**
  * acpigen_get_current() - Get the current ACPI code output pointer
  *
@@ -106,4 +111,31 @@ void acpigen_write_len_f(struct acpi_ctx *ctx);
  */
 void acpigen_pop_len(struct acpi_ctx *ctx);
 
+/**
+ * acpigen_write_package() - Start writing a package
+ *
+ * A package collects together a number of elements in the ACPI code. To write
+ * a package use:
+ *
+ * acpigen_write_package(ctx, 3);
+ * ...write things
+ * acpigen_pop_len()
+ *
+ * If you don't know the number of elements in advance, acpigen_write_package()
+ * returns a pointer to the value so you can update it later:
+ *
+ * char *num_elements = acpigen_write_package(ctx, 0);
+ * ...write things
+ * *num_elements += 1;
+ * ...write things
+ * *num_elements += 1;
+ * acpigen_pop_len()
+ *
+ * @ctx: ACPI context pointer
+ * @nr_el: Number of elements (0 if not known)
+ * @returns pointer to the number of elements, which can be updated by the
+ *	caller if needed
+ */
+char *acpigen_write_package(struct acpi_ctx *ctx, int nr_el);
+
 #endif

lib/acpi/acpigen.c

@@ -71,6 +71,18 @@ void acpigen_pop_len(struct acpi_ctx *ctx)
 	p[2] = len >> 12 & 0xff;
 }
 
+char *acpigen_write_package(struct acpi_ctx *ctx, int nr_el)
+{
+	char *p;
+
+	acpigen_emit_byte(ctx, PACKAGE_OP);
+	acpigen_write_len_f(ctx);
+	p = ctx->current;
+	acpigen_emit_byte(ctx, nr_el);
+
+	return p;
+}
+
 void acpigen_emit_stream(struct acpi_ctx *ctx, const char *data, int size)
 {
 	int i;

test/dm/acpigen.c

@@ -404,3 +404,30 @@ static int dm_test_acpi_len(struct unit_test_state *uts)
 	return 0;
 }
 DM_TEST(dm_test_acpi_len, 0);
+
+/* Test writing a package */
+static int dm_test_acpi_package(struct unit_test_state *uts)
+{
+	struct acpi_ctx *ctx;
+	char *num_elements;
+	u8 *ptr;
+
+	ut_assertok(alloc_context(&ctx));
+
+	ptr = acpigen_get_current(ctx);
+
+	num_elements = acpigen_write_package(ctx, 3);
+	ut_asserteq_ptr(num_elements, ptr + 4);
+
+	/* For ease of testing, just emit a byte, not valid package contents */
+	acpigen_emit_byte(ctx, 0x23);
+	acpigen_pop_len(ctx);
+	ut_asserteq(PACKAGE_OP, ptr[0]);
+	ut_asserteq(5, get_length(ptr + 1));
+	ut_asserteq(3, ptr[4]);
+
+	free_context(&ctx);
+
+	return 0;
+}
+DM_TEST(dm_test_acpi_package, 0);