summaryrefslogtreecommitdiffstats
path: root/Documentation/firmware-guide/acpi/namespace.rst
blob: 6193582a2204db02f16d928160709edb5b11d5fb (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
.. SPDX-License-Identifier: GPL-2.0
.. include:: <isonum.txt>

===================================================
ACPI Device Tree - Representation of ACPI Namespace
===================================================

:Copyright: |copy| 2013, Intel Corporation

:Author: Lv Zheng <lv.zheng@intel.com>

:Credit:   Thanks for the help from Zhang Rui <rui.zhang@intel.com> and
           Rafael J.Wysocki <rafael.j.wysocki@intel.com>.

Abstract
========
The Linux ACPI subsystem converts ACPI namespace objects into a Linux
device tree under the /sys/devices/LNXSYSTEM:00 and updates it upon
receiving ACPI hotplug notification events.  For each device object
in this hierarchy there is a corresponding symbolic link in the
/sys/bus/acpi/devices.

This document illustrates the structure of the ACPI device tree.

ACPI Definition Blocks
======================

The ACPI firmware sets up RSDP (Root System Description Pointer) in the
system memory address space pointing to the XSDT (Extended System
Description Table).  The XSDT always points to the FADT (Fixed ACPI
Description Table) using its first entry, the data within the FADT
includes various fixed-length entries that describe fixed ACPI features
of the hardware.  The FADT contains a pointer to the DSDT
(Differentiated System Descripition Table).  The XSDT also contains
entries pointing to possibly multiple SSDTs (Secondary System
Description Table).

The DSDT and SSDT data is organized in data structures called definition
blocks that contain definitions of various objects, including ACPI
control methods, encoded in AML (ACPI Machine Language).  The data block
of the DSDT along with the contents of SSDTs represents a hierarchical
data structure called the ACPI namespace whose topology reflects the
structure of the underlying hardware platform.

The relationships between ACPI System Definition Tables described above
are illustrated in the following diagram::

   +---------+    +-------+    +--------+    +------------------------+
   |  RSDP   | +->| XSDT  | +->|  FADT  |    |  +-------------------+ |
   +---------+ |  +-------+ |  +--------+  +-|->|       DSDT        | |
   | Pointer | |  | Entry |-+  | ...... |  | |  +-------------------+ |
   +---------+ |  +-------+    | X_DSDT |--+ |  | Definition Blocks | |
   | Pointer |-+  | ..... |    | ...... |    |  +-------------------+ |
   +---------+    +-------+    +--------+    |  +-------------------+ |
                  | Entry |------------------|->|       SSDT        | |
                  +- - - -+                  |  +-------------------| |
                  | Entry | - - - - - - - -+ |  | Definition Blocks | |
                  +- - - -+                | |  +-------------------+ |
                                           | |  +- - - - - - - - - -+ |
                                           +-|->|       SSDT        | |
                                             |  +-------------------+ |
                                             |  | Definition Blocks | |
                                             |  +- - - - - - - - - -+ |
                                             +------------------------+
                                                          |
                                             OSPM Loading |
                                                         \|/
                                                   +----------------+
                                                   | ACPI Namespace |
                                                   +----------------+

                  Figure 1. ACPI Definition Blocks

.. note:: RSDP can also contain a pointer to the RSDT (Root System
   Description Table).  Platforms provide RSDT to enable
   compatibility with ACPI 1.0 operating systems.  The OS is expected
   to use XSDT, if present.


Example ACPI Namespace
======================

All definition blocks are loaded into a single namespace.  The namespace
is a hierarchy of objects identified by names and paths.
The following naming conventions apply to object names in the ACPI
namespace:

   1. All names are 32 bits long.
   2. The first byte of a name must be one of 'A' - 'Z', '_'.
   3. Each of the remaining bytes of a name must be one of 'A' - 'Z', '0'
      - '9', '_'.
   4. Names starting with '_' are reserved by the ACPI specification.
   5. The '\' symbol represents the root of the namespace (i.e. names
      prepended with '\' are relative to the namespace root).
   6. The '^' symbol represents the parent of the current namespace node
      (i.e. names prepended with '^' are relative to the parent of the
      current namespace node).

The figure below shows an example ACPI namespace::

   +------+
   | \    |                     Root
   +------+
     |
     | +------+
     +-| _PR  |                 Scope(_PR): the processor namespace
     | +------+
     |   |
     |   | +------+
     |   +-| CPU0 |             Processor(CPU0): the first processor
     |     +------+
     |
     | +------+
     +-| _SB  |                 Scope(_SB): the system bus namespace
     | +------+
     |   |
     |   | +------+
     |   +-| LID0 |             Device(LID0); the lid device
     |   | +------+
     |   |   |
     |   |   | +------+
     |   |   +-| _HID |         Name(_HID, "PNP0C0D"): the hardware ID
     |   |   | +------+
     |   |   |
     |   |   | +------+
     |   |   +-| _STA |         Method(_STA): the status control method
     |   |     +------+
     |   |
     |   | +------+
     |   +-| PCI0 |             Device(PCI0); the PCI root bridge
     |     +------+
     |       |
     |       | +------+
     |       +-| _HID |         Name(_HID, "PNP0A08"): the hardware ID
     |       | +------+
     |       |
     |       | +------+
     |       +-| _CID |         Name(_CID, "PNP0A03"): the compatible ID
     |       | +------+
     |       |
     |       | +------+
     |       +-| RP03 |         Scope(RP03): the PCI0 power scope
     |       | +------+
     |       |   |
     |       |   | +------+
     |       |   +-| PXP3 |     PowerResource(PXP3): the PCI0 power resource
     |       |     +------+
     |       |
     |       | +------+
     |       +-| GFX0 |         Device(GFX0): the graphics adapter
     |         +------+
     |           |
     |           | +------+
     |           +-| _ADR |     Name(_ADR, 0x00020000): the PCI bus address
     |           | +------+
     |           |
     |           | +------+
     |           +-| DD01 |     Device(DD01): the LCD output device
     |             +------+
     |               |
     |               | +------+
     |               +-| _BCL | Method(_BCL): the backlight control method
     |                 +------+
     |
     | +------+
     +-| _TZ  |                 Scope(_TZ): the thermal zone namespace
     | +------+
     |   |
     |   | +------+
     |   +-| FN00 |             PowerResource(FN00): the FAN0 power resource
     |   | +------+
     |   |
     |   | +------+
     |   +-| FAN0 |             Device(FAN0): the FAN0 cooling device
     |   | +------+
     |   |   |
     |   |   | +------+
     |   |   +-| _HID |         Name(_HID, "PNP0A0B"): the hardware ID
     |   |     +------+
     |   |
     |   | +------+
     |   +-| TZ00 |             ThermalZone(TZ00); the FAN thermal zone
     |     +------+
     |
     | +------+
     +-| _GPE |                 Scope(_GPE): the GPE namespace
       +------+

                     Figure 2. Example ACPI Namespace


Linux ACPI Device Objects
=========================

The Linux kernel's core ACPI subsystem creates struct acpi_device
objects for ACPI namespace objects representing devices, power resources
processors, thermal zones.  Those objects are exported to user space via
sysfs as directories in the subtree under /sys/devices/LNXSYSTM:00.  The
format of their names is <bus_id:instance>, where 'bus_id' refers to the
ACPI namespace representation of the given object and 'instance' is used
for distinguishing different object of the same 'bus_id' (it is
two-digit decimal representation of an unsigned integer).

The value of 'bus_id' depends on the type of the object whose name it is
part of as listed in the table below::

                +---+-----------------+-------+----------+
                |   | Object/Feature  | Table | bus_id   |
                +---+-----------------+-------+----------+
                | N | Root            | xSDT  | LNXSYSTM |
                +---+-----------------+-------+----------+
                | N | Device          | xSDT  | _HID     |
                +---+-----------------+-------+----------+
                | N | Processor       | xSDT  | LNXCPU   |
                +---+-----------------+-------+----------+
                | N | ThermalZone     | xSDT  | LNXTHERM |
                +---+-----------------+-------+----------+
                | N | PowerResource   | xSDT  | LNXPOWER |
                +---+-----------------+-------+----------+
                | N | Other Devices   | xSDT  | device   |
                +---+-----------------+-------+----------+
                | F | PWR_BUTTON      | FADT  | LNXPWRBN |
                +---+-----------------+-------+----------+
                | F | SLP_BUTTON      | FADT  | LNXSLPBN |
                +---+-----------------+-------+----------+
                | M | Video Extension | xSDT  | LNXVIDEO |
                +---+-----------------+-------+----------+
                | M | ATA Controller  | xSDT  | LNXIOBAY |
                +---+-----------------+-------+----------+
                | M | Docking Station | xSDT  | LNXDOCK  |
                +---+-----------------+-------+----------+

                 Table 1. ACPI Namespace Objects Mapping

The following rules apply when creating struct acpi_device objects on
the basis of the contents of ACPI System Description Tables (as
indicated by the letter in the first column and the notation in the
second column of the table above):

   N:
      The object's source is an ACPI namespace node (as indicated by the
      named object's type in the second column).  In that case the object's
      directory in sysfs will contain the 'path' attribute whose value is
      the full path to the node from the namespace root.
   F:
      The struct acpi_device object is created for a fixed hardware
      feature (as indicated by the fixed feature flag's name in the second
      column), so its sysfs directory will not contain the 'path'
      attribute.
   M:
      The struct acpi_device object is created for an ACPI namespace node
      with specific control methods (as indicated by the ACPI defined
      device's type in the second column).  The 'path' attribute containing
      its namespace path will be present in its sysfs directory.  For
      example, if the _BCL method is present for an ACPI namespace node, a
      struct acpi_device object with LNXVIDEO 'bus_id' will be created for
      it.

The third column of the above table indicates which ACPI System
Description Tables contain information used for the creation of the
struct acpi_device objects represented by the given row (xSDT means DSDT
or SSDT).

The fourth column of the above table indicates the 'bus_id' generation
rule of the struct acpi_device object:

   _HID:
      _HID in the last column of the table means that the object's bus_id
      is derived from the _HID/_CID identification objects present under
      the corresponding ACPI namespace node. The object's sysfs directory
      will then contain the 'hid' and 'modalias' attributes that can be
      used to retrieve the _HID and _CIDs of that object.
   LNXxxxxx:
      The 'modalias' attribute is also present for struct acpi_device
      objects having bus_id of the "LNXxxxxx" form (pseudo devices), in
      which cases it contains the bus_id string itself.
   device:
      'device' in the last column of the table indicates that the object's
      bus_id cannot be determined from _HID/_CID of the corresponding
      ACPI namespace node, although that object represents a device (for
      example, it may be a PCI device with _ADR defined and without _HID
      or _CID).  In that case the string 'device' will be used as the
      object's bus_id.


Linux ACPI Physical Device Glue
===============================

ACPI device (i.e. struct acpi_device) objects may be linked to other
objects in the Linux' device hierarchy that represent "physical" devices
(for example, devices on the PCI bus).  If that happens, it means that
the ACPI device object is a "companion" of a device otherwise
represented in a different way and is used (1) to provide configuration
information on that device which cannot be obtained by other means and
(2) to do specific things to the device with the help of its ACPI
control methods.  One ACPI device object may be linked this way to
multiple "physical" devices.

If an ACPI device object is linked to a "physical" device, its sysfs
directory contains the "physical_node" symbolic link to the sysfs
directory of the target device object.  In turn, the target device's
sysfs directory will then contain the "firmware_node" symbolic link to
the sysfs directory of the companion ACPI device object.
The linking mechanism relies on device identification provided by the
ACPI namespace.  For example, if there's an ACPI namespace object
representing a PCI device (i.e. a device object under an ACPI namespace
object representing a PCI bridge) whose _ADR returns 0x00020000 and the
bus number of the parent PCI bridge is 0, the sysfs directory
representing the struct acpi_device object created for that ACPI
namespace object will contain the 'physical_node' symbolic link to the
/sys/devices/pci0000:00/0000:00:02:0/ sysfs directory of the
corresponding PCI device.

The linking mechanism is generally bus-specific.  The core of its
implementation is located in the drivers/acpi/glue.c file, but there are
complementary parts depending on the bus types in question located
elsewhere.  For example, the PCI-specific part of it is located in
drivers/pci/pci-acpi.c.


Example Linux ACPI Device Tree
=================================

The sysfs hierarchy of struct acpi_device objects corresponding to the
example ACPI namespace illustrated in Figure 2 with the addition of
fixed PWR_BUTTON/SLP_BUTTON devices is shown below::

   +--------------+---+-----------------+
   | LNXSYSTEM:00 | \ | acpi:LNXSYSTEM: |
   +--------------+---+-----------------+
     |
     | +-------------+-----+----------------+
     +-| LNXPWRBN:00 | N/A | acpi:LNXPWRBN: |
     | +-------------+-----+----------------+
     |
     | +-------------+-----+----------------+
     +-| LNXSLPBN:00 | N/A | acpi:LNXSLPBN: |
     | +-------------+-----+----------------+
     |
     | +-----------+------------+--------------+
     +-| LNXCPU:00 | \_PR_.CPU0 | acpi:LNXCPU: |
     | +-----------+------------+--------------+
     |
     | +-------------+-------+----------------+
     +-| LNXSYBUS:00 | \_SB_ | acpi:LNXSYBUS: |
     | +-------------+-------+----------------+
     |   |
     |   | +- - - - - - - +- - - - - - +- - - - - - - -+
     |   +-| PNP0C0D:00 | \_SB_.LID0 | acpi:PNP0C0D: |
     |   | +- - - - - - - +- - - - - - +- - - - - - - -+
     |   |
     |   | +------------+------------+-----------------------+
     |   +-| PNP0A08:00 | \_SB_.PCI0 | acpi:PNP0A08:PNP0A03: |
     |     +------------+------------+-----------------------+
     |       |
     |       | +-----------+-----------------+-----+
     |       +-| device:00 | \_SB_.PCI0.RP03 | N/A |
     |       | +-----------+-----------------+-----+
     |       |   |
     |       |   | +-------------+----------------------+----------------+
     |       |   +-| LNXPOWER:00 | \_SB_.PCI0.RP03.PXP3 | acpi:LNXPOWER: |
     |       |     +-------------+----------------------+----------------+
     |       |
     |       | +-------------+-----------------+----------------+
     |       +-| LNXVIDEO:00 | \_SB_.PCI0.GFX0 | acpi:LNXVIDEO: |
     |         +-------------+-----------------+----------------+
     |           |
     |           | +-----------+-----------------+-----+
     |           +-| device:01 | \_SB_.PCI0.DD01 | N/A |
     |             +-----------+-----------------+-----+
     |
     | +-------------+-------+----------------+
     +-| LNXSYBUS:01 | \_TZ_ | acpi:LNXSYBUS: |
       +-------------+-------+----------------+
         |
         | +-------------+------------+----------------+
         +-| LNXPOWER:0a | \_TZ_.FN00 | acpi:LNXPOWER: |
         | +-------------+------------+----------------+
         |
         | +------------+------------+---------------+
         +-| PNP0C0B:00 | \_TZ_.FAN0 | acpi:PNP0C0B: |
         | +------------+------------+---------------+
         |
         | +-------------+------------+----------------+
         +-| LNXTHERM:00 | \_TZ_.TZ00 | acpi:LNXTHERM: |
           +-------------+------------+----------------+

                  Figure 3. Example Linux ACPI Device Tree

.. note:: Each node is represented as "object/path/modalias", where:

   1. 'object' is the name of the object's directory in sysfs.
   2. 'path' is the ACPI namespace path of the corresponding
      ACPI namespace object, as returned by the object's 'path'
      sysfs attribute.
   3. 'modalias' is the value of the object's 'modalias' sysfs
      attribute (as described earlier in this document).

.. note:: N/A indicates the device object does not have the 'path' or the
   'modalias' attribute.