It describes the basic concepts of NVDIMM ACPI and the interface
between QEMU and the ACPI BIOS
Signed-off-by: Xiao Guangrong <guangrong.xiao@xxxxxxxxxxxxxxx>
---
docs/specs/acpi_nvdimm.txt | 179 +++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 179 insertions(+)
create mode 100644 docs/specs/acpi_nvdimm.txt
diff --git a/docs/specs/acpi_nvdimm.txt b/docs/specs/acpi_nvdimm.txt
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+QEMU<->ACPI BIOS NVDIMM interface
+---------------------------------
+
+QEMU supports NVDIMM via ACPI. This document describes the basic concepts of
+NVDIMM ACPI and the interface between QEMU and the ACPI BIOS.
+
+NVDIMM ACPI Background
+----------------------
+NVDIMM is introduced in ACPI 6.0 which defines an NVDIMM root device under
+_SB scope with a _HID of “ACPI0012”. For each NVDIMM present or intended
+to be supported by platform, platform firmware also exposes an ACPI
+Namespace Device under the root device.
+
+The NVDIMM child devices under the NVDIMM root device are defined with _ADR
+corresponding to the NFIT device handle. The NVDIMM root device and the
+NVDIMM devices can have device specific methods (_DSM) to provide additional
+functions specific to a particular NVDIMM implementation.
+
+This is an example from ACPI 6.0, a platform contains one NVDIMM:
+
+Scope (\_SB){
+ Device (NVDR) // Root device
+ {
+ Name (_HID, “ACPI0012”)
+ Method (_STA) {...}
+ Method (_FIT) {...}
+ Method (_DSM, ...) {...}
+ Device (NVD)
+ {
+ Name(_ADR, h) //where h is NFIT Device Handle for this NVDIMM
+ Method (_DSM, ...) {...}
+ }
+ }
+}
+
+Methods supported on both NVDIMM root device and NVDIMM device are
+1) _STA(Status)
+ It returns the current status of a device, which can be one of the
+ following: enabled, disabled, or removed.
+
+ Arguments: None
+
+ Return Value:
+ It returns an An Integer which is defined as followings:
+ Bit [0] – Set if the device is present.
+ Bit [1] – Set if the device is enabled and decoding its resources.
+ Bit [2] – Set if the device should be shown in the UI.
+ Bit [3] – Set if the device is functioning properly (cleared if device
+ failed its diagnostics).
+ Bit [4] – Set if the battery is present.
+ Bits [31:5] – Reserved (must be cleared).
+
+2) _DSM (Device Specific Method)
+ It is a control method that enables devices to provide device specific
+ control functions that are consumed by the device driver.
+ The NVDIMM DSM specification can be found at:
+ http://pmem.io/documents/NVDIMM_DSM_Interface_Example.pdf
+
+ Arguments:
+ Arg0 – A Buffer containing a UUID (16 Bytes)
+ Arg1 – An Integer containing the Revision ID (4 Bytes)
+ Arg2 – An Integer containing the Function Index (4 Bytes)
+ Arg3 – A package containing parameters for the function specified by the
+ UUID, Revision ID, and Function Index
+
+ Return Value:
+ If Function Index = 0, a Buffer containing a function index bitfield.
+ Otherwise, the return value and type depends on the UUID, revision ID
+ and function index which are described in the DSM specification.
+
+Methods on NVDIMM ROOT Device
+_FIT(Firmware Interface Table)
+ It evaluates to a buffer returning data in the format of a series of NFIT
+ Type Structure.
+
+ Arguments: None
+
+ Return Value:
+ A Buffer containing a list of NFIT Type structure entries.
+
+ The detailed definition of the structure can be found at ACPI 6.0: 5.2.25
+ NVDIMM Firmware Interface Table (NFIT).
+
+QEMU NVDIMM Implemention
+========================
+QEMU reserves a page starting from 0xFF00000 and 4 bytes IO Port starting
+from 0x0a18 for NVDIMM ACPI.
+
+Memory 0xFF00000 - 0xFF00FFF:
+ This page is RAM-based and it is used to transfer data between _DSM
+ method and QEMU. If ACPI has control, this pages is owned by ACPI which
+ writes _DSM input data to it, otherwise, it is owned by QEMU which
+ emulates _DSM access and writes the output data to it.
+
+ ACPI Writes _DSM Input Data:
+ [0xFF00000 - 0xFF00003]: 4 bytes, NVDIMM Devcie Handle, 0 is reserved
+ for NVDIMM Root device.
+ [0xFF00004 - 0xFF00007]: 4 bytes, Revision ID, that is the Arg1 of _DSM
+ method.
+ [0xFF00008 - 0xFF0000B]: 4 bytes. Function Index, that is the Arg2 of
+ _DSM method.
+ [0xFF0000C - 0xFF00FFF]: 4084 bytes, the Arg3 of _DSM method
+
+ QEMU Writes Output Data:
+ [0xFF00000 - 0xFF00FFF]: the DSM return result filled by QEMU
+
+IO Port 0x0a18 - 0xa1b:
+ ACPI uses it to transfer control from guest to QEMU and read the size
+ of return result filled by QEMU
+
+ Read Access:
+ [0x0a18 - 0xa1b]: 4 bytes, the buffer size of _DSM output data.
+
+_DSM process diagram:
+---------------------
+The page, 0xFF00000 - 0xFF00FFF, is used by _DSM Virtualization.
+
+ +----------------------+ +-----------------------+
+ | 1. OSPM | | 2. OSPM |
+ | save _DSM input data | | read 0x0a18 | Exit to QEMU
+ | to the page +----->| +------------+
+ | | | | |
+ +----------------------+ +-----------------------+ |
+ |
+ v
+ +------------- ----+ +-----------+ +------------------+--------+
+ | 5 QEMU | | 4 QEMU | | 3. QEMU |
+ | write _DSM result | | emulate | | get _DSM input parameters |
+ | to the page +<------+ _DSM +<-----+ from the page |
+ | | | | | |
+ +--------+-----------+ +-----------+ +---------------------------+
+ |
+ | Enter Guest
+ |
+ v
+ +--------------------------+ +--------------+
+ | 6 OSPM | | 7 OSPM |
+ | result size is returned | | _DSM return |
+ | by read and get DSM +----->+ |
+ | result from the page | | |
+ +--------------------------+ +--------------+
+
+ 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 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 |
+ +----------+-------------+-------------+-----------------------------------+
+ | length | 4 | 4 | the length of FIT buffer read out |
+ +----------+-------------+-------------+-----------------------------------+
+ | fit data | Varies | 8 | FIT data, its size is indicated |
+ | | | | by length field above |
+ +----------+-------------+-------------+-----------------------------------+
+
+ 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
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