[PATCH v1 1/2] ACPI: utils: Add api to read _SUB from ACPI

[Stefan Binding <sbinding@opensource.cirrus.com>]

Add a wrapper function to read the _SUB string from ACPI.

Signed-off-by: Stefan Binding <sbinding@opensource.cirrus.com>
---
 drivers/acpi/utils.c | 26 ++++++++++++++++++++++++++
 include/linux/acpi.h |  8 ++++++++
 2 files changed, 34 insertions(+)

diff --git a/drivers/acpi/utils.c b/drivers/acpi/utils.c
index 3a9773a09e19..5d1bdb79e372 100644
--- a/drivers/acpi/utils.c
+++ b/drivers/acpi/utils.c
@@ -291,6 +291,32 @@ int acpi_get_local_address(acpi_handle handle, u32 *addr)
 }
 EXPORT_SYMBOL(acpi_get_local_address);
 
+int acpi_get_sub(acpi_handle handle, char *sub, size_t size)
+{
+	struct acpi_buffer buffer = { ACPI_ALLOCATE_BUFFER, NULL };
+	union acpi_object *obj;
+	acpi_status status;
+	int ret;
+
+	status = acpi_evaluate_object(handle, METHOD_NAME__SUB, NULL, &buffer);
+	if (!ACPI_SUCCESS(status)) {
+		acpi_handle_debug(handle, "Reading ACPI _SUB failed: %#x\n", status);
+		return -ENOENT;
+	}
+
+	obj = buffer.pointer;
+	if (obj->type == ACPI_TYPE_STRING) {
+		ret = strscpy(sub, obj->string.pointer, size);
+	} else {
+		acpi_handle_warn(handle, "Warning ACPI _SUB did not return a string\n");
+		ret = -EINVAL;
+	}
+	acpi_os_free(buffer.pointer);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(acpi_get_sub);
+
 acpi_status
 acpi_evaluate_reference(acpi_handle handle,
 			acpi_string pathname,
diff --git a/include/linux/acpi.h b/include/linux/acpi.h
index 4f82a5bc6d98..9bf18adf5920 100644
--- a/include/linux/acpi.h
+++ b/include/linux/acpi.h
@@ -21,6 +21,8 @@
 #endif
 #include <acpi/acpi.h>
 
+#define ACPI_MAX_SUB_BUF_SIZE	9
+
 #ifdef	CONFIG_ACPI
 
 #include <linux/list.h>
@@ -762,6 +764,7 @@ static inline u64 acpi_arch_get_root_pointer(void)
 #endif
 
 int acpi_get_local_address(acpi_handle handle, u32 *addr);
+int acpi_get_sub(acpi_handle handle, char *sub, size_t size);
 
 #else	/* !CONFIG_ACPI */
 
@@ -1023,6 +1026,11 @@ static inline int acpi_get_local_address(acpi_handle handle, u32 *addr)
 	return -ENODEV;
 }
 
+static int acpi_get_sub(acpi_handle handle, char *sub, size_t size)
+{
+	return -ENODEV;
+}
+
 static inline int acpi_register_wakeup_handler(int wake_irq,
 	bool (*wakeup)(void *context), void *context)
 {
-- 
2.25.1