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

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

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;
 };
 
 /**

lib/acpi/acpigen.c

@@ -10,6 +10,7 @@
 
 #include <common.h>
 #include <dm.h>
+#include <log.h>
 #include <acpi/acpigen.h>
 #include <dm/acpi.h>
 
@@ -38,6 +39,38 @@ void acpigen_emit_dword(struct acpi_ctx *ctx, uint data)
 	acpigen_emit_byte(ctx, (data >> 24) & 0xff);
 }
 
+/*
+ * Maximum length for an ACPI object generated by this code,
+ *
+ * If you need to change this, change acpigen_write_len_f(ctx) and
+ * acpigen_pop_len(ctx)
+ */
+#define ACPIGEN_MAXLEN 0xfffff
+
+void acpigen_write_len_f(struct acpi_ctx *ctx)
+{
+	assert(ctx->ltop < (ACPIGEN_LENSTACK_SIZE - 1));
+	ctx->len_stack[ctx->ltop++] = ctx->current;
+	acpigen_emit_byte(ctx, 0);
+	acpigen_emit_byte(ctx, 0);
+	acpigen_emit_byte(ctx, 0);
+}
+
+void acpigen_pop_len(struct acpi_ctx *ctx)
+{
+	int len;
+	char *p;
+
+	assert(ctx->ltop > 0);
+	p = ctx->len_stack[--ctx->ltop];
+	len = ctx->current - (void *)p;
+	assert(len <= ACPIGEN_MAXLEN);
+	/* generate store length for 0xfffff max */
+	p[0] = ACPI_PKG_LEN_3_BYTES | (len & 0xf);
+	p[1] = len >> 4 & 0xff;
+	p[2] = len >> 12 & 0xff;
+}
+
 void acpigen_emit_stream(struct acpi_ctx *ctx, const char *data, int size)
 {
 	int i;

test/dm/acpigen.c

@@ -25,7 +25,7 @@
 #define TEST_STRING	"frogmore"
 #define TEST_STREAM2	"\xfa\xde"
 
-static int alloc_context(struct acpi_ctx **ctxp)
+static int alloc_context_size(struct acpi_ctx **ctxp, int size)
 {
 	struct acpi_ctx *ctx;
 
@@ -33,17 +33,23 @@ static int alloc_context(struct acpi_ctx **ctxp)
 	ctx = malloc(sizeof(*ctx));
 	if (!ctx)
 		return -ENOMEM;
-	ctx->base = malloc(ACPI_CONTEXT_SIZE);
+	ctx->base = malloc(size);
 	if (!ctx->base) {
 		free(ctx);
 		return -ENOMEM;
 	}
+	ctx->ltop = 0;
 	ctx->current = ctx->base;
 	*ctxp = ctx;
 
 	return 0;
 }
 
+static int alloc_context(struct acpi_ctx **ctxp)
+{
+	return alloc_context_size(ctxp, ACPI_CONTEXT_SIZE);
+}
+
 static void free_context(struct acpi_ctx **ctxp)
 {
 	free((*ctxp)->base);
@@ -344,3 +350,57 @@ static int dm_test_acpi_spi(struct unit_test_state *uts)
 	return 0;
 }
 DM_TEST(dm_test_acpi_spi, DM_TESTF_SCAN_PDATA | DM_TESTF_SCAN_FDT);
+
+/**
+ * get_length() - decode a three-byte length field
+ *
+ * @ptr: Length encoded as per ACPI
+ * @return decoded length, or -EINVAL on error
+ */
+static int get_length(u8 *ptr)
+{
+	if (!(*ptr & 0x80))
+		return -EINVAL;
+
+	return (*ptr & 0xf) | ptr[1] << 4 | ptr[2] << 12;
+}
+
+/* Test emitting a length */
+static int dm_test_acpi_len(struct unit_test_state *uts)
+{
+	const int size = 0xc0000;
+	struct acpi_ctx *ctx;
+	u8 *ptr;
+	int i;
+
+	ut_assertok(alloc_context_size(&ctx, size));
+
+	ptr = acpigen_get_current(ctx);
+
+	/* Write a byte and a 3-byte length */
+	acpigen_write_len_f(ctx);
+	acpigen_emit_byte(ctx, 0x23);
+	acpigen_pop_len(ctx);
+	ut_asserteq(1 + 3, get_length(ptr));
+
+	/* Write 200 bytes so we need two length bytes */
+	ptr = ctx->current;
+	acpigen_write_len_f(ctx);
+	for (i = 0; i < 200; i++)
+		acpigen_emit_byte(ctx, 0x23);
+	acpigen_pop_len(ctx);
+	ut_asserteq(200 + 3, get_length(ptr));
+
+	/* Write 40KB so we need three length bytes */
+	ptr = ctx->current;
+	acpigen_write_len_f(ctx);
+	for (i = 0; i < 40000; i++)
+		acpigen_emit_byte(ctx, 0x23);
+	acpigen_pop_len(ctx);
+	ut_asserteq(40000 + 3, get_length(ptr));
+
+	free_context(&ctx);
+
+	return 0;
+}
+DM_TEST(dm_test_acpi_len, 0);