diff --git a/include/hardware/hardware.h b/include/hardware/hardware.h
index 7774b2b..db6640d 100644
--- a/include/hardware/hardware.h
+++ b/include/hardware/hardware.h
@@ -47,11 +47,40 @@
     /** tag must be initialized to HARDWARE_MODULE_TAG */
     uint32_t tag;
 
-    /** major version number for the module */
-    uint16_t version_major;
+    /**
+     * The API version of the implemented module. The module owner is
+     * responsible for updating the version when a module interface has
+     * changed.
+     *
+     * The derived modules such as gralloc and audio own and manage this field.
+     * The module user must interpret the version field to decide whether or
+     * not to inter-operate with the supplied module implementation.
+     * For example, SurfaceFlinger is responsible for making sure that
+     * it knows how to manage different versions of the gralloc-module API,
+     * and AudioFlinger must know how to do the same for audio-module API.
+     *
+     * The module API version should include a major and a minor component.
+     * For example, version 1.0 could be represented as 0x0100. This format
+     * implies that versions 0x0100-0x01ff are all API-compatible.
+     *
+     * In the future, libhardware will expose a hw_get_module_version()
+     * (or equivalent) function that will take minimum/maximum supported
+     * versions as arguments and would be able to reject modules with
+     * versions outside of the supplied range.
+     */
+    uint16_t module_api_version;
 
-    /** minor version number of the module */
-    uint16_t version_minor;
+    /**
+     * The API version of the HAL module interface. This is meant to
+     * version the hw_module_t, hw_module_methods_t, and hw_device_t
+     * structures and definitions.
+     *
+     * The HAL interface owns this field. Module users/implementations
+     * must NOT rely on this value for version information.
+     *
+     * Presently, 0 is the only valid value.
+     */
+    uint16_t hal_api_version;
 
     /** Identifier of module */
     const char *id;
@@ -88,7 +117,22 @@
     /** tag must be initialized to HARDWARE_DEVICE_TAG */
     uint32_t tag;
 
-    /** version number for hw_device_t */
+    /**
+     * Version of the module-specific device API. This value is used by
+     * the derived-module user to manage different device implementations.
+     *
+     * The module user is responsible for checking the module_api_version
+     * and device version fields to ensure that the user is capable of
+     * communicating with the specific module implementation.
+     *
+     * One module can support multiple devices with different versions. This
+     * can be useful when a device interface changes in an incompatible way
+     * but it is still necessary to support older implementations at the same
+     * time. One such example is the Camera 2.0 API.
+     *
+     * This field is interpreted by the module user and is ignored by the
+     * HAL interface itself.
+     */
     uint32_t version;
 
     /** reference to the module this device belongs to */