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Improve the description and clearly document the length field Suggested-by: Igor Mammedov <imammedo@redhat.com> Signed-off-by: Xiao Guangrong <guangrong.xiao@linux.intel.com> Reviewed-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: Michael S. Tsirkin <mst@redhat.com> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com> Reviewed-by: Igor Mammedov <imammedo@redhat.com>
188 lines
8.2 KiB
Plaintext
188 lines
8.2 KiB
Plaintext
QEMU<->ACPI BIOS NVDIMM interface
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---------------------------------
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QEMU supports NVDIMM via ACPI. This document describes the basic concepts of
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NVDIMM ACPI and the interface between QEMU and the ACPI BIOS.
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NVDIMM ACPI Background
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----------------------
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NVDIMM is introduced in ACPI 6.0 which defines an NVDIMM root device under
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_SB scope with a _HID of “ACPI0012”. For each NVDIMM present or intended
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to be supported by platform, platform firmware also exposes an ACPI
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Namespace Device under the root device.
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The NVDIMM child devices under the NVDIMM root device are defined with _ADR
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corresponding to the NFIT device handle. The NVDIMM root device and the
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NVDIMM devices can have device specific methods (_DSM) to provide additional
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functions specific to a particular NVDIMM implementation.
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This is an example from ACPI 6.0, a platform contains one NVDIMM:
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Scope (\_SB){
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Device (NVDR) // Root device
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{
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Name (_HID, “ACPI0012”)
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Method (_STA) {...}
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Method (_FIT) {...}
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Method (_DSM, ...) {...}
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Device (NVD)
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{
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Name(_ADR, h) //where h is NFIT Device Handle for this NVDIMM
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Method (_DSM, ...) {...}
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}
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}
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}
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Method supported on both NVDIMM root device and NVDIMM device
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_DSM (Device Specific Method)
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It is a control method that enables devices to provide device specific
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control functions that are consumed by the device driver.
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The NVDIMM DSM specification can be found at:
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http://pmem.io/documents/NVDIMM_DSM_Interface_Example.pdf
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Arguments:
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Arg0 – A Buffer containing a UUID (16 Bytes)
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Arg1 – An Integer containing the Revision ID (4 Bytes)
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Arg2 – An Integer containing the Function Index (4 Bytes)
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Arg3 – A package containing parameters for the function specified by the
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UUID, Revision ID, and Function Index
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Return Value:
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If Function Index = 0, a Buffer containing a function index bitfield.
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Otherwise, the return value and type depends on the UUID, revision ID
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and function index which are described in the DSM specification.
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Methods on NVDIMM ROOT Device
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_FIT(Firmware Interface Table)
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It evaluates to a buffer returning data in the format of a series of NFIT
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Type Structure.
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Arguments: None
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Return Value:
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A Buffer containing a list of NFIT Type structure entries.
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The detailed definition of the structure can be found at ACPI 6.0: 5.2.25
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NVDIMM Firmware Interface Table (NFIT).
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QEMU NVDIMM Implementation
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==========================
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QEMU uses 4 bytes IO Port starting from 0x0a18 and a RAM-based memory page
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for NVDIMM ACPI.
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Memory:
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QEMU uses BIOS Linker/loader feature to ask BIOS to allocate a memory
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page and dynamically patch its into a int32 object named "MEMA" in ACPI.
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This page is RAM-based and it is used to transfer data between _DSM
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method and QEMU. If ACPI has control, this pages is owned by ACPI which
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writes _DSM input data to it, otherwise, it is owned by QEMU which
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emulates _DSM access and writes the output data to it.
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ACPI writes _DSM Input Data (based on the offset in the page):
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[0x0 - 0x3]: 4 bytes, NVDIMM Device Handle.
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The handle is completely QEMU internal thing, the values in
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range [1, 0xFFFF] indicate nvdimm device. Other values are
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reserved for other purposes.
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Reserved handles:
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0 is reserved for nvdimm root device named NVDR.
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0x10000 is reserved for QEMU internal DSM function called on
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the root device.
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[0x4 - 0x7]: 4 bytes, Revision ID, that is the Arg1 of _DSM method.
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[0x8 - 0xB]: 4 bytes. Function Index, that is the Arg2 of _DSM method.
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[0xC - 0xFFF]: 4084 bytes, the Arg3 of _DSM method.
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QEMU Writes Output Data (based on the offset in the page):
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[0x0 - 0x3]: 4 bytes, the length of result
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[0x4 - 0xFFF]: 4092 bytes, the DSM result filled by QEMU
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IO Port 0x0a18 - 0xa1b:
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ACPI writes the address of the memory page allocated by BIOS to this
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port then QEMU gets the control and fills the result in the memory page.
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write Access:
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[0x0a18 - 0xa1b]: 4 bytes, the address of the memory page allocated
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by BIOS.
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_DSM process diagram:
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---------------------
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"MEMA" indicates the address of memory page allocated by BIOS.
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+----------------------+ +-----------------------+
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| 1. OSPM | | 2. OSPM |
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| save _DSM input data | | write "MEMA" to | Exit to QEMU
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| to the page +----->| IO port 0x0a18 +------------+
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| indicated by "MEMA" | | | |
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+----------------------+ +-----------------------+ |
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v
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+------------- ----+ +-----------+ +------------------+--------+
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| 5 QEMU | | 4 QEMU | | 3. QEMU |
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| write _DSM result | | emulate | | get _DSM input data from |
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| to the page +<------+ _DSM +<-----+ the page indicated by the |
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| | | | | value from the IO port |
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+--------+-----------+ +-----------+ +---------------------------+
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| Enter Guest
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v
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+--------------------------+ +--------------+
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| 6 OSPM | | 7 OSPM |
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| result size is returned | | _DSM return |
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| by reading DSM +----->+ |
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| result from the page | | |
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+--------------------------+ +--------------+
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NVDIMM hotplug
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--------------
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ACPI BIOS GPE.4 handler is dedicated for notifying OS about nvdimm device
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hot-add event.
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QEMU internal use only _DSM function
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------------------------------------
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1) Read FIT
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_FIT method uses _DSM method to fetch NFIT structures blob from QEMU
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in 1 page sized increments which are then concatenated and returned
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as _FIT method result.
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Input parameters:
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Arg0 – UUID {set to 648B9CF2-CDA1-4312-8AD9-49C4AF32BD62}
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Arg1 – Revision ID (set to 1)
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Arg2 - Function Index, 0x1
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Arg3 - A package containing a buffer whose layout is as follows:
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+----------+--------+--------+-------------------------------------------+
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| Field | Length | Offset | Description |
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+----------+--------+--------+-------------------------------------------+
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| offset | 4 | 0 | offset in QEMU's NFIT structures blob to |
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| | | | read from |
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+----------+--------+--------+-------------------------------------------+
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Output layout in the dsm memory page:
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+----------+--------+--------+-------------------------------------------+
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| Field | Length | Offset | Description |
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+----------+--------+--------+-------------------------------------------+
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| length | 4 | 0 | length of entire returned data |
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| | | | (including this header) |
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+----------+-----------------+-------------------------------------------+
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| | | | return status codes |
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| | | | 0x0 - success |
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| | | | 0x100 - error caused by NFIT update while |
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| status | 4 | 4 | read by _FIT wasn't completed, other |
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| | | | codes follow Chapter 3 in DSM Spec Rev1 |
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+----------+-----------------+-------------------------------------------+
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| fit data | Varies | 8 | contains FIT data, this field is present |
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| | | | if status field is 0; |
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+----------+--------+--------+-------------------------------------------+
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The FIT offset is maintained by the OSPM itself, current offset plus
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the size of the fit data returned by the function is the next offset
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OSPM should read. When all FIT data has been read out, zero fit data
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size is returned.
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If it returns status code 0x100, OSPM should restart to read FIT (read
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from offset 0 again).
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