| 1 | QEMU<->ACPI BIOS NVDIMM interface |
| 2 | ================================= |
| 3 | |
| 4 | QEMU supports NVDIMM via ACPI. This document describes the basic concepts of |
| 5 | NVDIMM ACPI and the interface between QEMU and the ACPI BIOS. |
| 6 | |
| 7 | NVDIMM ACPI Background |
| 8 | ---------------------- |
| 9 | |
| 10 | NVDIMM is introduced in ACPI 6.0 which defines an NVDIMM root device under |
| 11 | _SB scope with a _HID of "ACPI0012". For each NVDIMM present or intended |
| 12 | to be supported by platform, platform firmware also exposes an ACPI |
| 13 | Namespace Device under the root device. |
| 14 | |
| 15 | The NVDIMM child devices under the NVDIMM root device are defined with _ADR |
| 16 | corresponding to the NFIT device handle. The NVDIMM root device and the |
| 17 | NVDIMM devices can have device specific methods (_DSM) to provide additional |
| 18 | functions specific to a particular NVDIMM implementation. |
| 19 | |
| 20 | This is an example from ACPI 6.0, a platform contains one NVDIMM:: |
| 21 | |
| 22 | Scope (\_SB){ |
| 23 | Device (NVDR) // Root device |
| 24 | { |
| 25 | Name (_HID, "ACPI0012") |
| 26 | Method (_STA) {...} |
| 27 | Method (_FIT) {...} |
| 28 | Method (_DSM, ...) {...} |
| 29 | Device (NVD) |
| 30 | { |
| 31 | Name(_ADR, h) //where h is NFIT Device Handle for this NVDIMM |
| 32 | Method (_DSM, ...) {...} |
| 33 | } |
| 34 | } |
| 35 | } |
| 36 | |
| 37 | Methods supported on both NVDIMM root device and NVDIMM device |
| 38 | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ |
| 39 | |
| 40 | _DSM (Device Specific Method) |
| 41 | It is a control method that enables devices to provide device specific |
| 42 | control functions that are consumed by the device driver. |
| 43 | The NVDIMM DSM specification can be found at |
| 44 | http://pmem.io/documents/NVDIMM_DSM_Interface_Example.pdf |
| 45 | |
| 46 | Arguments: |
| 47 | |
| 48 | Arg0 |
| 49 | A Buffer containing a UUID (16 Bytes) |
| 50 | Arg1 |
| 51 | An Integer containing the Revision ID (4 Bytes) |
| 52 | Arg2 |
| 53 | An Integer containing the Function Index (4 Bytes) |
| 54 | Arg3 |
| 55 | A package containing parameters for the function specified by the |
| 56 | UUID, Revision ID, and Function Index |
| 57 | |
| 58 | Return Value: |
| 59 | |
| 60 | If Function Index = 0, a Buffer containing a function index bitfield. |
| 61 | Otherwise, the return value and type depends on the UUID, revision ID |
| 62 | and function index which are described in the DSM specification. |
| 63 | |
| 64 | Methods on NVDIMM ROOT Device |
| 65 | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ |
| 66 | |
| 67 | _FIT(Firmware Interface Table) |
| 68 | It evaluates to a buffer returning data in the format of a series of NFIT |
| 69 | Type Structure. |
| 70 | |
| 71 | Arguments: None |
| 72 | |
| 73 | Return Value: |
| 74 | A Buffer containing a list of NFIT Type structure entries. |
| 75 | |
| 76 | The detailed definition of the structure can be found at ACPI 6.0: 5.2.25 |
| 77 | NVDIMM Firmware Interface Table (NFIT). |
| 78 | |
| 79 | QEMU NVDIMM Implementation |
| 80 | -------------------------- |
| 81 | |
| 82 | QEMU uses 4 bytes IO Port starting from 0x0a18 and a RAM-based memory page |
| 83 | for NVDIMM ACPI. |
| 84 | |
| 85 | Memory: |
| 86 | QEMU uses BIOS Linker/loader feature to ask BIOS to allocate a memory |
| 87 | page and dynamically patch its address into an int32 object named "MEMA" |
| 88 | in ACPI. |
| 89 | |
| 90 | This page is RAM-based and it is used to transfer data between _DSM |
| 91 | method and QEMU. If ACPI has control, this pages is owned by ACPI which |
| 92 | writes _DSM input data to it, otherwise, it is owned by QEMU which |
| 93 | emulates _DSM access and writes the output data to it. |
| 94 | |
| 95 | ACPI writes _DSM Input Data (based on the offset in the page): |
| 96 | |
| 97 | [0x0 - 0x3] |
| 98 | 4 bytes, NVDIMM Device Handle. |
| 99 | |
| 100 | The handle is completely QEMU internal thing, the values in |
| 101 | range [1, 0xFFFF] indicate nvdimm device. Other values are |
| 102 | reserved for other purposes. |
| 103 | |
| 104 | Reserved handles: |
| 105 | |
| 106 | - 0 is reserved for nvdimm root device named NVDR. |
| 107 | - 0x10000 is reserved for QEMU internal DSM function called on |
| 108 | the root device. |
| 109 | |
| 110 | [0x4 - 0x7] |
| 111 | 4 bytes, Revision ID, that is the Arg1 of _DSM method. |
| 112 | |
| 113 | [0x8 - 0xB] |
| 114 | 4 bytes. Function Index, that is the Arg2 of _DSM method. |
| 115 | |
| 116 | [0xC - 0xFFF] |
| 117 | 4084 bytes, the Arg3 of _DSM method. |
| 118 | |
| 119 | QEMU writes Output Data (based on the offset in the page): |
| 120 | |
| 121 | [0x0 - 0x3] |
| 122 | 4 bytes, the length of result |
| 123 | |
| 124 | [0x4 - 0xFFF] |
| 125 | 4092 bytes, the DSM result filled by QEMU |
| 126 | |
| 127 | IO Port 0x0a18 - 0xa1b: |
| 128 | ACPI writes the address of the memory page allocated by BIOS to this |
| 129 | port then QEMU gets the control and fills the result in the memory page. |
| 130 | |
| 131 | Write Access: |
| 132 | |
| 133 | [0x0a18 - 0xa1b] |
| 134 | 4 bytes, the address of the memory page allocated by BIOS. |
| 135 | |
| 136 | _DSM process diagram |
| 137 | -------------------- |
| 138 | |
| 139 | "MEMA" indicates the address of memory page allocated by BIOS. |
| 140 | |
| 141 | :: |
| 142 | |
| 143 | +----------------------+ +-----------------------+ |
| 144 | | 1. OSPM | | 2. OSPM | |
| 145 | | save _DSM input data | | write "MEMA" to | Exit to QEMU |
| 146 | | to the page +----->| IO port 0x0a18 +------------+ |
| 147 | | indicated by "MEMA" | | | | |
| 148 | +----------------------+ +-----------------------+ | |
| 149 | | |
| 150 | v |
| 151 | +--------------------+ +-----------+ +------------------+--------+ |
| 152 | | 5 QEMU | | 4 QEMU | | 3. QEMU | |
| 153 | | write _DSM result | | emulate | | get _DSM input data from | |
| 154 | | to the page +<------+ _DSM +<-----+ the page indicated by the | |
| 155 | | | | | | value from the IO port | |
| 156 | +--------+-----------+ +-----------+ +---------------------------+ |
| 157 | | |
| 158 | | Enter Guest |
| 159 | | |
| 160 | v |
| 161 | +--------------------------+ +--------------+ |
| 162 | | 6 OSPM | | 7 OSPM | |
| 163 | | result size is returned | | _DSM return | |
| 164 | | by reading DSM +----->+ | |
| 165 | | result from the page | | | |
| 166 | +--------------------------+ +--------------+ |
| 167 | |
| 168 | NVDIMM hotplug |
| 169 | -------------- |
| 170 | |
| 171 | ACPI BIOS GPE.4 handler is dedicated for notifying OS about nvdimm device |
| 172 | hot-add event. |
| 173 | |
| 174 | QEMU internal use only _DSM functions |
| 175 | ------------------------------------- |
| 176 | |
| 177 | Read FIT |
| 178 | ^^^^^^^^ |
| 179 | |
| 180 | _FIT method uses _DSM method to fetch NFIT structures blob from QEMU |
| 181 | in 1 page sized increments which are then concatenated and returned |
| 182 | as _FIT method result. |
| 183 | |
| 184 | Input parameters: |
| 185 | |
| 186 | Arg0 |
| 187 | UUID {set to 648B9CF2-CDA1-4312-8AD9-49C4AF32BD62} |
| 188 | Arg1 |
| 189 | Revision ID (set to 1) |
| 190 | Arg2 |
| 191 | Function Index, 0x1 |
| 192 | Arg3 |
| 193 | A package containing a buffer whose layout is as follows: |
| 194 | |
| 195 | +----------+--------+--------+-------------------------------------------+ |
| 196 | | Field | Length | Offset | Description | |
| 197 | +----------+--------+--------+-------------------------------------------+ |
| 198 | | offset | 4 | 0 | offset in QEMU's NFIT structures blob to | |
| 199 | | | | | read from | |
| 200 | +----------+--------+--------+-------------------------------------------+ |
| 201 | |
| 202 | Output layout in the dsm memory page: |
| 203 | |
| 204 | +----------+--------+--------+-------------------------------------------+ |
| 205 | | Field | Length | Offset | Description | |
| 206 | +----------+--------+--------+-------------------------------------------+ |
| 207 | | length | 4 | 0 | length of entire returned data | |
| 208 | | | | | (including this header) | |
| 209 | +----------+--------+--------+-------------------------------------------+ |
| 210 | | | | | return status codes | |
| 211 | | | | | | |
| 212 | | | | | - 0x0 - success | |
| 213 | | | | | - 0x100 - error caused by NFIT update | |
| 214 | | status | 4 | 4 | while read by _FIT wasn't completed | |
| 215 | | | | | - other codes follow Chapter 3 in | |
| 216 | | | | | DSM Spec Rev1 | |
| 217 | +----------+--------+--------+-------------------------------------------+ |
| 218 | | fit data | Varies | 8 | contains FIT data. This field is present | |
| 219 | | | | | if status field is 0. | |
| 220 | +----------+--------+--------+-------------------------------------------+ |
| 221 | |
| 222 | The FIT offset is maintained by the OSPM itself, current offset plus |
| 223 | the size of the fit data returned by the function is the next offset |
| 224 | OSPM should read. When all FIT data has been read out, zero fit data |
| 225 | size is returned. |
| 226 | |
| 227 | If it returns status code 0x100, OSPM should restart to read FIT (read |
| 228 | from offset 0 again). |