acpigen: Support writing a length

It is convenient to write a length value for preceding a block of data.
Of course the length is not known or is hard to calculate a priori. So add
a way to mark the start on a stack, so the length can be updated when
known.

Signed-off-by: Simon Glass <[email protected]>
Reviewed-by: Wolfgang Wallner <[email protected]>
Reviewed-by: Bin Meng <[email protected]>

2 files changed, 49 insertions, 1 deletions

diff --git a/include/acpi/acpigen.h b/include/acpi/acpigen.h
index 9c1faf7bf2b..18409b613c6 100644
--- a/include/acpi/acpigen.h
+++ b/include/acpi/acpigen.h
@@ -14,6 +14,9 @@
 
 struct acpi_ctx;
 
+/* Top 4 bits of the value used to indicate a three-byte length value */
+#define ACPI_PKG_LEN_3_BYTES	0x80
+
 /**
  * acpigen_get_current() - Get the current ACPI code output pointer
  *
@@ -65,4 +68,42 @@ void acpigen_emit_stream(struct acpi_ctx *ctx, const char *data, int size);
  */
 void acpigen_emit_string(struct acpi_ctx *ctx, const char *str);
 
+/**
+ * acpigen_write_len_f() - Write a 'forward' length placeholder
+ *
+ * This adds space for a length value in the ACPI stream and pushes the current
+ * position (before the length) on the stack. After calling this you can write
+ * some data and then call acpigen_pop_len() to update the length value.
+ *
+ * Usage:
+ *
+ *    acpigen_write_len_f() ------\
+ *    acpigen_write...()          |
+ *    acpigen_write...()          |
+ *      acpigen_write_len_f() --\ |
+ *      acpigen_write...()      | |
+ *      acpigen_write...()      | |
+ *      acpigen_pop_len() ------/ |
+ *    acpigen_write...()          |
+ *    acpigen_pop_len() ----------/
+ *
+ * See ACPI 6.3 section 20.2.4 Package Length Encoding
+ *
+ * This implementation always uses a 3-byte packet length for simplicity. It
+ * could be adjusted to support other lengths.
+ *
+ * @ctx: ACPI context pointer
+ */
+void acpigen_write_len_f(struct acpi_ctx *ctx);
+
+/**
+ * acpigen_pop_len() - Update the previously stacked length placeholder
+ *
+ * Call this after the data for the block has been written. It updates the
+ * top length value in the stack and pops it off.
+ *
+ * @ctx: ACPI context pointer
+ */
+void acpigen_pop_len(struct acpi_ctx *ctx);
+
 #endif
diff --git a/include/dm/acpi.h b/include/dm/acpi.h
index 696b1a96a09..dfda88e4931 100644
--- a/include/dm/acpi.h
+++ b/include/dm/acpi.h
@@ -16,12 +16,15 @@
 #define ACPI_OPS_PTR(_ptr)
 #endif
 
-/* Length of an ACPI name string, excluding nul terminator */
+/* Length of an ACPI name string, excluding null terminator */
 #define ACPI_NAME_LEN	4
 
 /* Length of an ACPI name string including nul terminator */
 #define ACPI_NAME_MAX	(ACPI_NAME_LEN + 1)
 
+/* Number of nested objects supported */
+#define ACPIGEN_LENSTACK_SIZE 10
+
 #if !defined(__ACPI__)
 
 /**
@@ -35,6 +38,8 @@
  *	adding a new table. The RSDP holds pointers to the RSDT and XSDT.
  * @rsdt: Pointer to the Root System Description Table
  * @xsdt: Pointer to the Extended System Description Table
+ * @len_stack: Stack of 'length' words to fix up later
+ * @ltop: Points to current top of stack (0 = empty)
  */
 struct acpi_ctx {
 	void *base;
@@ -42,6 +47,8 @@ struct acpi_ctx {
 	struct acpi_rsdp *rsdp;
 	struct acpi_rsdt *rsdt;
 	struct acpi_xsdt *xsdt;
+	char *len_stack[ACPIGEN_LENSTACK_SIZE];
+	int ltop;
 };
 
 /**