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diff --git a/docs/specs/acpi_nvdimm.rst b/docs/specs/acpi_nvdimm.rst new file mode 100644 index 0000000000..ab0335253d --- /dev/null +++ b/docs/specs/acpi_nvdimm.rst @@ -0,0 +1,228 @@ +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). |