commit 84d35492b145cebc000f8fd72818eb25b8e65c04
author Stewart Miles <smiles@google.com> Thu May 01 09:03:27 2014 -0700
committer Stewart Miles <smiles@google.com> Mon May 12 12:35:37 2014 -0700
tree 0a7adfd3f93de27984377aa1e210685540891ff8
parent 4c847f2b79d99b1fecf487b167dd5bbe3ea7da06

Described restrictions for common HAL object methods.

Inheritance of HAL object is performed by composing a child structure of a
single parent structure located at offset 0 followed by new data members
and function pointers in the child structure.

For example,

struct child {
  struct parent common;
  int a_data_member;
  void (*a_method)(struct child *c, int v);
};

HAL code assumes this layout when accessing child structures given a pointer
to a parent structure such that users write code like the following...

void child_method(struct *parent, int v) {
  struct child * c = (struct child*)parent;
  // do stuff with c
}

Code above will break if a member is added before "common" in "struct child".

This change adds comments that describe the restriction on the location of
parent HAL objects within a derived HAL object.  HAL objects that already
have comments that describe the required location of parent objects are not
modified.

Change-Id: Ibe4300275286ef275b2097534c84f1029d761d87

include/hardware/hdmi_cec.h

diff --git a/include/hardware/hdmi_cec.h b/include/hardware/hdmi_cec.h
index f049952..1906153 100644
--- a/include/hardware/hdmi_cec.h
+++ b/include/hardware/hdmi_cec.h
@@ -211,6 +211,11 @@
 typedef void (*event_callback_t)(const hdmi_event_t* event, void* arg);
 
 typedef struct hdmi_cec_module {
+    /**
+     * Common methods of the HDMI CEC module.  This *must* be the first member of
+     * hdmi_cec_module as users of this structure will cast a hw_module_t to hdmi_cec_module
+     * pointer in contexts where it's known the hw_module_t references a hdmi_cec_module.
+     */
     struct hw_module_t common;
 } hdmi_module_t;
 
@@ -218,6 +223,11 @@
  * HDMI-CEC HAL interface definition.
  */
 typedef struct hdmi_cec_device {
+    /**
+     * Common methods of the HDMI CEC device.  This *must* be the first member of
+     * hdmi_cec_device as users of this structure will cast a hw_device_t to hdmi_cec_device
+     * pointer in contexts where it's known the hw_device_t references a hdmi_cec_device.
+     */
     struct hw_device_t common;
 
     /*