| 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 |
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ |
| |
| _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 Implementation |
| -------------------------- |
| |
| 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 address into an 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. |
| |
| The handle is completely QEMU internal thing, the values in |
| range [1, 0xFFFF] indicate nvdimm device. Other values are |
| reserved for other purposes. |
| |
| Reserved handles: |
| |
| - 0 is reserved for nvdimm root device named NVDR. |
| - 0x10000 is reserved for QEMU internal DSM function called on |
| the 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 | | | |
| +--------------------------+ +--------------+ |
| |
| NVDIMM hotplug |
| -------------- |
| |
| ACPI BIOS GPE.4 handler is dedicated for notifying OS about nvdimm device |
| hot-add event. |
| |
| QEMU internal use only _DSM functions |
| ------------------------------------- |
| |
| Read FIT |
| ^^^^^^^^ |
| |
| _FIT method uses _DSM method to fetch NFIT structures blob from QEMU |
| in 1 page sized increments which are then concatenated and returned |
| as _FIT method result. |
| |
| Input parameters: |
| |
| Arg0 |
| UUID {set to 648B9CF2-CDA1-4312-8AD9-49C4AF32BD62} |
| Arg1 |
| Revision ID (set to 1) |
| Arg2 |
| Function Index, 0x1 |
| Arg3 |
| A package containing a buffer whose layout is as follows: |
| |
| +----------+--------+--------+-------------------------------------------+ |
| | Field | Length | Offset | Description | |
| +----------+--------+--------+-------------------------------------------+ |
| | offset | 4 | 0 | offset in QEMU's NFIT structures blob to | |
| | | | | read from | |
| +----------+--------+--------+-------------------------------------------+ |
| |
| Output layout in the dsm memory page: |
| |
| +----------+--------+--------+-------------------------------------------+ |
| | Field | Length | Offset | Description | |
| +----------+--------+--------+-------------------------------------------+ |
| | length | 4 | 0 | length of entire returned data | |
| | | | | (including this header) | |
| +----------+--------+--------+-------------------------------------------+ |
| | | | | return status codes | |
| | | | | | |
| | | | | - 0x0 - success | |
| | | | | - 0x100 - error caused by NFIT update | |
| | status | 4 | 4 | while read by _FIT wasn't completed | |
| | | | | - other codes follow Chapter 3 in | |
| | | | | DSM Spec Rev1 | |
| +----------+--------+--------+-------------------------------------------+ |
| | fit data | Varies | 8 | contains FIT data. This field is present | |
| | | | | if status field is 0. | |
| +----------+--------+--------+-------------------------------------------+ |
| |
| The FIT offset is maintained by the OSPM itself, current offset plus |
| the size of the fit data returned by the function is the next offset |
| OSPM should read. When all FIT data has been read out, zero fit data |
| size is returned. |
| |
| If it returns status code 0x100, OSPM should restart to read FIT (read |
| from offset 0 again). |
