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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). |