It describes the basic concepts of NVDIMM ACPI and the interfaces
between QEMU and the ACPI BIOS
Signed-off-by: Xiao Guangrong <guangrong.xiao@xxxxxxxxxxxxxxx>
---
docs/specs/acpi_nvdimm.txt | 132 +++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 132 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, ...) {...}
+ }
+ }
+}
+
+Method supported on both NVDIMM root device and NVDIMM device
+_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 uses 4 bytes IO Port starting from 0x0a18 and a RAM-based memory page
+for NVDIMM ACPI.
+
+Memory:
+ QEMU uses BIOS Linker/loader feature to ask BIOS to allocate a memory
+ page and dynamically patch its into a int32 object named "MEMA" in ACPI.
+
+ 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 (based on the offset in the page):
+ [0x0 - 0x3]: 4 bytes, NVDIMM Device Handle, 0 is reserved for NVDIMM
+ Root device.
+ [0x4 - 0x7]: 4 bytes, Revision ID, that is the Arg1 of _DSM method.
+ [0x8 - 0xB]: 4 bytes. Function Index, that is the Arg2 of _DSM method.
+ [0xC - 0xFFF]: 4084 bytes, the Arg3 of _DSM method.
+
+ QEMU Writes Output Data (based on the offset in the page):
+ [0x0 - 0x3]: 4 bytes, the length of result
+ [0x4 - 0xFFF]: 4092 bytes, the DSM result filled by QEMU
+
+IO Port 0x0a18 - 0xa1b:
+ ACPI writes the address of the memory page allocated by BIOS to this
+ port then QEMU gets the control and fills the result in the memory page.
+
+ write Access:
+ [0x0a18 - 0xa1b]: 4 bytes, the address of the memory page allocated
+ by BIOS.
+
+_DSM process diagram:
+---------------------
+"MEMA" indicates the address of memory page allocated by BIOS.
+
+ +----------------------+ +-----------------------+
+ | 1. OSPM | | 2. OSPM |
+ | save _DSM input data | | write "MEMA" to | Exit to QEMU
+ | to the page +----->| IO port 0x0a18 +------------+
+ | indicated by "MEMA" | | | |
+ +----------------------+ +-----------------------+ |
+ |
+ v
+ +------------- ----+ +-----------+ +------------------+--------+
+ | 5 QEMU | | 4 QEMU | | 3. QEMU |
+ | write _DSM result | | emulate | | get _DSM input data from |
+ | to the page +<------+ _DSM +<-----+ the page indicated by the |
+ | | | | | value from the IO port |
+ +--------+-----------+ +-----------+ +---------------------------+
+ |
+ | Enter Guest
+ |
+ v
+ +--------------------------+ +--------------+
+ | 6 OSPM | | 7 OSPM |
+ | result size is returned | | _DSM return |
+ | by reading DSM +----->+ |
+ | result from the page | | |
+ +--------------------------+ +--------------+
+
+ _FIT implementation
+ -------------------
+ TODO (will fill it when nvdimm hotplug is introduced)
\ No newline at end of file
--
1.8.3.1
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