ACPI, APEI, Document for APEI

Add document for APEI, including kernel parameters and EINJ debug file
sytem interface.

Signed-off-by: Huang Ying <ying.huang@intel.com>
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>

Documentation/acpi/apei/einj.txt

@@ -0,0 +1,49 @@
+			APEI Error INJection
+			~~~~~~~~~~~~~~~~~~~~
+
+EINJ provides a hardware error injection mechanism
+It is very useful for debugging and testing of other APEI and RAS features.
+
+To use EINJ, make sure the following are enabled in your kernel
+configuration:
+
+CONFIG_DEBUG_FS
+CONFIG_ACPI_APEI
+CONFIG_ACPI_APEI_EINJ
+
+The user interface of EINJ is debug file system, under the
+directory apei/einj. The following files are provided.
+
+- available_error_type
+  Reading this file returns the error injection capability of the
+  platform, that is, which error types are supported. The error type
+  definition is as follow, the left field is the error type value, the
+  right field is error description.
+
+    0x00000001	Processor Correctable
+    0x00000002	Processor Uncorrectable non-fatal
+    0x00000004	Processor Uncorrectable fatal
+    0x00000008  Memory Correctable
+    0x00000010  Memory Uncorrectable non-fatal
+    0x00000020  Memory Uncorrectable fatal
+    0x00000040	PCI Express Correctable
+    0x00000080	PCI Express Uncorrectable fatal
+    0x00000100	PCI Express Uncorrectable non-fatal
+    0x00000200	Platform Correctable
+    0x00000400	Platform Uncorrectable non-fatal
+    0x00000800	Platform Uncorrectable fatal
+
+  The format of file contents are as above, except there are only the
+  available error type lines.
+
+- error_type
+  This file is used to set the error type value. The error type value
+  is defined in "available_error_type" description.
+
+- error_inject
+  Write any integer to this file to trigger the error
+  injection. Before this, please specify all necessary error
+  parameters.
+
+For more information about EINJ, please refer to ACPI specification
+version 4.0, section 17.5.