diff --git a/Documentation/acpi/apei/einj.txt b/Documentation/acpi/apei/einj.txt
index e20b6daaced4..a58b63da1a36 100644
--- a/Documentation/acpi/apei/einj.txt
+++ b/Documentation/acpi/apei/einj.txt
@@ -47,11 +47,16 @@ directory apei/einj. The following files are provided.
 
 - param1
   This file is used to set the first error parameter value. Effect of
-  parameter depends on error_type specified.
+  parameter depends on error_type specified. For example, if error
+  type is memory related type, the param1 should be a valid physical
+  memory address.
 
 - param2
   This file is used to set the second error parameter value. Effect of
-  parameter depends on error_type specified.
+  parameter depends on error_type specified. For example, if error
+  type is memory related type, the param2 should be a physical memory
+  address mask. Linux requires page or narrower granularity, say,
+  0xfffffffffffff000.
 
 - notrigger
   The EINJ mechanism is a two step process. First inject the error, then