acpi: add utility acpi_keyvalue to retrieve from _DSM

Adapt code written for AMBA acpi driver to generic case for fetching
key/value pairs from _DSM method.

Signed-off-by: Brandon Anderson <brandon.anderson@amd.com>
Signed-off-by: Graeme Gregory <graeme.gregory@linaro.org>
Acked-by: Tomasz Nowicki <tomasz.nowicki@linaro.org>

3 files changed, 124 insertions, 0 deletions

diff --git a/drivers/acpi/Makefile b/drivers/acpi/Makefile
index 3433c9e9ca75..8f584067d0ad 100644
--- a/drivers/acpi/Makefile
+++ b/drivers/acpi/Makefile
@@ -15,6 +15,7 @@ obj-$(CONFIG_X86)		+= blacklist.o
 # ACPI Core Subsystem (Interpreter)
 #
 obj-y				+= acpi.o \
+					acpi_keyvalue.o \
 					acpica/
 
 # All the builtin files are in the "acpi." module_param namespace.
diff --git a/drivers/acpi/acpi_keyvalue.c b/drivers/acpi/acpi_keyvalue.c
new file mode 100644
index 000000000000..5c3cde921b22
--- /dev/null
+++ b/drivers/acpi/acpi_keyvalue.c
@@ -0,0 +1,115 @@
+/*
+ * Key/Value handler from _DSM method
+ *
+ * Copyright (C) 2013 Linaro Ltd
+ *
+ * Author: Graeme Gregory <graeme.gregory@linaro.org>
+ *
+ * Original based on code :-
+ *
+ * Copyright (C) 2013 Advanced Micro Devices, Inc.
+ *
+ * Author: Brandon Anderson <brandon.anderson@amd.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include <linux/acpi.h>
+
+/* UUID: a706b112-bf0b-48d2-9fa3-95591a3c4c06 (randomly generated) */
+static const char acpi_amba_dsm_uuid[] = {
+	0xa7, 0x06, 0xb1, 0x12, 0xbf, 0x0b, 0x48, 0xd2,
+	0x9f, 0xa3, 0x95, 0x59, 0x1a, 0x3c, 0x4c, 0x06
+};
+
+/* acpi_dsm_lookup_value()
+ *
+ * Helper to parse through ACPI _DSM object for a device. Each entry
+ * has three fields.
+ */
+int acpi_dsm_lookup_value(acpi_handle handle,
+		const char *tag, int index,
+		struct acpi_dsm_entry *entry)
+{
+	acpi_status status;
+	struct acpi_object_list input;
+	struct acpi_buffer output = { ACPI_ALLOCATE_BUFFER, NULL };
+	union acpi_object params[4];
+	union acpi_object *obj;
+	int len, match_count, i;
+
+	/* invalidate output in case there's no entry to supply */
+	entry->key = NULL;
+	entry->value = NULL;
+
+	if (!acpi_has_method(handle, "_DSM"))
+		return -ENOENT;
+
+	input.count = 4;
+	params[0].type = ACPI_TYPE_BUFFER;		/* UUID */
+	params[0].buffer.length = sizeof(acpi_amba_dsm_uuid);
+	params[0].buffer.pointer = (char *)acpi_amba_dsm_uuid;
+	params[1].type = ACPI_TYPE_INTEGER;		/* Revision */
+	params[1].integer.value = 1;
+	params[2].type = ACPI_TYPE_INTEGER;		/* Function # */
+	params[2].integer.value = 1;
+	params[3].type = ACPI_TYPE_PACKAGE;		/* Arguments */
+	params[3].package.count = 0;
+	params[3].package.elements = NULL;
+	input.pointer = params;
+
+	status = acpi_evaluate_object_typed(handle, "_DSM",
+			&input, &output, ACPI_TYPE_PACKAGE);
+	if (ACPI_FAILURE(status)) {
+		pr_err("failed to get _DSM package for this device\n");
+		return -ENOENT;
+	}
+
+	obj = (union acpi_object *)output.pointer;
+
+	/* parse 2 objects per entry */
+	match_count = 0;
+	for (i = 0; (i + 2) <= obj->package.count; i += 2) {
+		/* key must be a string */
+		len = obj->package.elements[i].string.length;
+		if (len <= 0)
+			continue;
+
+		/* check to see if this is the entry to return */
+		if (strncmp(tag, obj->package.elements[i].string.pointer,
+				len) != 0 ||
+				match_count < index) {
+			match_count++;
+			continue;
+		}
+
+		/* copy the key */
+		entry->key = kmalloc(len + 1, GFP_KERNEL);
+		strncpy(entry->key,
+				obj->package.elements[i].string.pointer,
+				len);
+		entry->key[len] = '\0';
+
+		/* value is a string with space-delimited fields if necessary */
+		len = obj->package.elements[i + 1].string.length;
+		if (len > 0) {
+			entry->value = kmalloc(len + 1, GFP_KERNEL);
+			strncpy(entry->value,
+				obj->package.elements[i+1].string.pointer,
+				len);
+			entry->value[len] = '\0';
+		}
+
+		break;
+	}
+
+	kfree(output.pointer);
+
+	if (entry->key == NULL)
+		return -ENOENT;
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(acpi_dsm_lookup_value);
diff --git a/include/linux/acpi.h b/include/linux/acpi.h
index 651abc4cde29..ca3290d22b78 100644
--- a/include/linux/acpi.h
+++ b/include/linux/acpi.h
@@ -446,6 +446,14 @@ static inline bool acpi_driver_match_device(struct device *dev,
 
 int acpi_device_uevent_modalias(struct device *, struct kobj_uevent_env *);
 int acpi_device_modalias(struct device *, char *, int);
+struct acpi_dsm_entry {
+	char *key;
+	char *value;
+};
+
+int acpi_dsm_lookup_value(acpi_handle handle,
+		const char *tag, int index,
+		struct acpi_dsm_entry *entry);
 
 #define ACPI_PTR(_ptr)	(_ptr)