Camera: clarify external camera device ID requirements

Bug: 64874137
Change-Id: Ibf45a0077952d2ec42cdef80659a019b6d24051f
diff --git a/camera/provider/2.4/ICameraProvider.hal b/camera/provider/2.4/ICameraProvider.hal
index 3015b7d..abb6366 100644
--- a/camera/provider/2.4/ICameraProvider.hal
+++ b/camera/provider/2.4/ICameraProvider.hal
@@ -35,22 +35,23 @@
  * where
  *   - <major>/<minor> is the provider HAL HIDL version,
  *   - <type> is the type of devices this provider knows about, such as
- *     "internal", "legacy", "usb", or "remote"
+ *     "internal", "legacy", "external", or "remote"
  *   - <instance> is a non-negative integer starting from 0 to disambiguate
  *     between multiple HALs of the same type.
  *
  * The "legacy" type is only used for passthrough legacy HAL mode, and must
  * not be used by a standalone binderized HAL.
  *
- * The device instance names enumerated by the provider must be of the form
+ * The device instance names enumerated by the provider in getCameraIdList() or
+ * ICameraProviderCallback::cameraDeviceStatusChange() must be of the form
  * "device@<major>.<minor>/<type>/<id>" where
  * <major>/<minor> is the HIDL version of the interface. <id> is either a small
  * incrementing integer for "internal" device types, with 0 being the main
  * back-facing camera and 1 being the main front-facing camera, if they exist.
- * Or, for external devices such as type "usb", a unique serial number that can
- * be used to identify the device reliably when it is disconnected and
- * reconnected. Multiple providers may not enumerate the same device ID.
+ * Or, for external devices, a unique serial number (if possible) that can be
+ * used to identify the device reliably when it is disconnected and reconnected.
  *
+ * Multiple providers must not enumerate the same device ID.
  */
 interface ICameraProvider {
 
@@ -97,7 +98,7 @@
     getVendorTags() generates (Status status, vec<VendorTagSection> sections);
 
     /**
-     * getCameraDeviceList:
+     * getCameraIdList:
      *
      * Returns the list of internal camera device interfaces known to this
      * camera provider. These devices can then be accessed via the hardware