[PATCH v2 8/8] nvdimm docs: add nvdimm Read FIT function

[Xiao Guangrong <guangrong.xiao@linux.intel.com>]

Add the specification of Read FIT function

Signed-off-by: Xiao Guangrong <guangrong.xiao@linux.intel.com>
---
 docs/specs/acpi_nvdimm.txt | 38 +++++++++++++++++++++++++++++++++++---
 1 file changed, 35 insertions(+), 3 deletions(-)

diff --git a/docs/specs/acpi_nvdimm.txt b/docs/specs/acpi_nvdimm.txt
index 0fdd251..1a31b19 100644
--- a/docs/specs/acpi_nvdimm.txt
+++ b/docs/specs/acpi_nvdimm.txt
@@ -127,6 +127,38 @@ _DSM process diagram:
  | result from the page     |      |              |
  +--------------------------+      +--------------+
 
- _FIT implementation
- -------------------
- TODO (will fill it when nvdimm hotplug is introduced)
+ QEMU internal use only _DSM function
+ ------------------------------------
+ There is the function introduced by QEMU and only used by QEMU internal.
+
+ 1) Read FIT
+ As we only reserved one page for NVDIMM ACPI it is impossible to map the
+ whole FIT data to guest's address space. This function is for NVDIMM root
+ device and is used by _FIT method to read a piece of FIT data from QEMU.
+
+ Input parameters:
+ Arg0 – UUID {set to 2f10e7a4-9e91-11e4-89d3-123b93f75cba}
+ Arg1 – Revision ID (set to 1)
+ Arg2 - 0xFFFFFFFF
+ Arg3 - A package containing a buffer whose layout is as follows:
+
+ +----------+-------------+-------------+-----------------------------------+
+ |  Filed   | Byte Length | Byte Offset | Description                       |
+ +----------+-------------+-------------+-----------------------------------+
+ | offset   | 4           | 0           | the offset of FIT buffer          |
+ +----------+-------------+-------------+-----------------------------------+
+
+ Output:
+ +----------+-------------+-------------+-----------------------------------+
+ |  Filed   | Byte Length | Byte Offset | Description                       |
+ +----------+-------------+-------------+-----------------------------------+
+ | status   | 4           | 0           | return status codes following     |
+ |          |             |             | Chapter 3 in DSM Spec Rev1        |
+ +----------+-------------+-------------+-----------------------------------+
+ | fit data | Varies      | 8           | FIT data                          |
+ |          |             |             |                                   |
+ +----------+-------------+-------------+-----------------------------------+
+
+ The FIT offset is maintained by the caller itself, current offset plugs
+ the length returned by the function is the next offset we should read.
+ When all the FIT data has been read out, zero length is returned.
-- 
1.8.3.1