summaryrefslogtreecommitdiff
path: root/Documentation/devicetree/bindings/arm/idle-states.txt
blob: 45730ba60af5411f1f0c13a8d3078d37a9b94c25 (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
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
==========================================
ARM idle states binding description
==========================================

==========================================
1 - Introduction
==========================================

ARM systems contain HW capable of managing power consumption dynamically,
where cores can be put in different low-power states (ranging from simple
wfi to power gating) according to OS PM policies. The CPU states representing
the range of dynamic idle states that a processor can enter at run-time, can be
specified through device tree bindings representing the parameters required
to enter/exit specific idle states on a given processor.

According to the Server Base System Architecture document (SBSA, [3]), the
power states an ARM CPU can be put into are identified by the following list:

- Running
- Idle_standby
- Idle_retention
- Sleep
- Off

The power states described in the SBSA document define the basic CPU states on
top of which ARM platforms implement power management schemes that allow an OS
PM implementation to put the processor in different idle states (which include
states listed above; "off" state is not an idle state since it does not have
wake-up capabilities, hence it is not considered in this document).

Idle state parameters (eg entry latency) are platform specific and need to be
characterized with bindings that provide the required information to OS PM
code so that it can build the required tables and use them at runtime.

The device tree binding definition for ARM idle states is the subject of this
document.

===========================================
2 - idle-states definitions
===========================================

Idle states are characterized for a specific system through a set of
timing and energy related properties, that underline the HW behaviour
triggered upon idle states entry and exit.

The following diagram depicts the CPU execution phases and related timing
properties required to enter and exit an idle state:

..__[EXEC]__|__[PREP]__|__[ENTRY]__|__[IDLE]__|__[EXIT]__|__[EXEC]__..
	    |          |           |          |          |

	    |<------ entry ------->|
	    |       latency        |
					      |<- exit ->|
					      |  latency |
	    |<-------- min-residency -------->|
		       |<-------  wakeup-latency ------->|

		Diagram 1: CPU idle state execution phases

EXEC:	Normal CPU execution.

PREP:	Preparation phase before committing the hardware to idle mode
	like cache flushing. This is abortable on pending wake-up
	event conditions. The abort latency is assumed to be negligible
	(i.e. less than the ENTRY + EXIT duration). If aborted, CPU
	goes back to EXEC. This phase is optional. If not abortable,
	this should be included in the ENTRY phase instead.

ENTRY:	The hardware is committed to idle mode. This period must run
	to completion up to IDLE before anything else can happen.

IDLE:	This is the actual energy-saving idle period. This may last
	between 0 and infinite time, until a wake-up event occurs.

EXIT:	Period during which the CPU is brought back to operational
	mode (EXEC).

entry-latency: Worst case latency required to enter the idle state. The
exit-latency may be guaranteed only after entry-latency has passed.

min-residency: Minimum period, including preparation and entry, for a given
idle state to be worthwhile energywise.

wakeup-latency: Maximum delay between the signaling of a wake-up event and the
CPU being able to execute normal code again. If not specified, this is assumed
to be entry-latency + exit-latency.

These timing parameters can be used by an OS in different circumstances.

An idle CPU requires the expected min-residency time to select the most
appropriate idle state based on the expected expiry time of the next IRQ
(ie wake-up) that causes the CPU to return to the EXEC phase.

An operating system scheduler may need to compute the shortest wake-up delay
for CPUs in the system by detecting how long will it take to get a CPU out
of an idle state, eg:

wakeup-delay = exit-latency + max(entry-latency - (now - entry-timestamp), 0)

In other words, the scheduler can make its scheduling decision by selecting
(eg waking-up) the CPU with the shortest wake-up latency.
The wake-up latency must take into account the entry latency if that period
has not expired. The abortable nature of the PREP period can be ignored
if it cannot be relied upon (e.g. the PREP deadline may occur much sooner than
the worst case since it depends on the CPU operating conditions, ie caches
state).

An OS has to reliably probe the wakeup-latency since some devices can enforce
latency constraints guarantees to work properly, so the OS has to detect the
worst case wake-up latency it can incur if a CPU is allowed to enter an
idle state, and possibly to prevent that to guarantee reliable device
functioning.

The min-residency time parameter deserves further explanation since it is
expressed in time units but must factor in energy consumption coefficients.

The energy consumption of a cpu when it enters a power state can be roughly
characterised by the following graph:

               |
               |
               |
           e   |
           n   |                                      /---
           e   |                               /------
           r   |                        /------
           g   |                  /-----
           y   |           /------
               |       ----
               |      /|
               |     / |
               |    /  |
               |   /   |
               |  /    |
               | /     |
               |/      |
          -----|-------+----------------------------------
              0|       1                              time(ms)

		Graph 1: Energy vs time example

The graph is split in two parts delimited by time 1ms on the X-axis.
The graph curve with X-axis values = { x | 0 < x < 1ms } has a steep slope
and denotes the energy costs incurred while entering and leaving the idle
state.
The graph curve in the area delimited by X-axis values = {x | x > 1ms } has
shallower slope and essentially represents the energy consumption of the idle
state.

min-residency is defined for a given idle state as the minimum expected
residency time for a state (inclusive of preparation and entry) after
which choosing that state become the most energy efficient option. A good
way to visualise this, is by taking the same graph above and comparing some
states energy consumptions plots.

For sake of simplicity, let's consider a system with two idle states IDLE1,
and IDLE2:

          |
          |
          |
          |                                                  /-- IDLE1
       e  |                                              /---
       n  |                                         /----
       e  |                                     /---
       r  |                                /-----/--------- IDLE2
       g  |                    /-------/---------
       y  |        ------------    /---|
          |       /           /----    |
          |      /        /---         |
          |     /    /----             |
          |    / /---                  |
          |   ---                      |
          |  /                         |
          | /                          |
          |/                           |                  time
       ---/----------------------------+------------------------
          |IDLE1-energy < IDLE2-energy | IDLE2-energy < IDLE1-energy
                                       |
                                IDLE2-min-residency

		Graph 2: idle states min-residency example

In graph 2 above, that takes into account idle states entry/exit energy
costs, it is clear that if the idle state residency time (ie time till next
wake-up IRQ) is less than IDLE2-min-residency, IDLE1 is the better idle state
choice energywise.

This is mainly down to the fact that IDLE1 entry/exit energy costs are lower
than IDLE2.

However, the lower power consumption (ie shallower energy curve slope) of idle
state IDLE2 implies that after a suitable time, IDLE2 becomes more energy
efficient.

The time at which IDLE2 becomes more energy efficient than IDLE1 (and other
shallower states in a system with multiple idle states) is defined
IDLE2-min-residency and corresponds to the time when energy consumption of
IDLE1 and IDLE2 states breaks even.

The definitions provided in this section underpin the idle states
properties specification that is the subject of the following sections.

===========================================
3 - idle-states node
===========================================

ARM processor idle states are defined within the idle-states node, which is
a direct child of the cpus node [1] and provides a container where the
processor idle states, defined as device tree nodes, are listed.

- idle-states node

	Usage: Optional - On ARM systems, it is a container of processor idle
			  states nodes. If the system does not provide CPU
			  power management capabilities or the processor just
			  supports idle_standby an idle-states node is not
			  required.

	Description: idle-states node is a container node, where its
		     subnodes describe the CPU idle states.

	Node name must be "idle-states".

	The idle-states node's parent node must be the cpus node.

	The idle-states node's child nodes can be:

	- one or more state nodes

	Any other configuration is considered invalid.

	An idle-states node defines the following properties:

	- entry-method
		Value type: <stringlist>
		Usage and definition depend on ARM architecture version.
			# On ARM v8 64-bit this property is required and must
			  be:
			   - "psci"
			# On ARM 32-bit systems this property is optional

The nodes describing the idle states (state) can only be defined within the
idle-states node, any other configuration is considered invalid and therefore
must be ignored.

===========================================
4 - state node
===========================================

A state node represents an idle state description and must be defined as
follows:

- state node

	Description: must be child of the idle-states node

	The state node name shall follow standard device tree naming
	rules ([5], 2.2.1 "Node names"), in particular state nodes which
	are siblings within a single common parent must be given a unique name.

	The idle state entered by executing the wfi instruction (idle_standby
	SBSA,[3][4]) is considered standard on all ARM platforms and therefore
	must not be listed.

	With the definitions provided above, the following list represents
	the valid properties for a state node:

	- compatible
		Usage: Required
		Value type: <stringlist>
		Definition: Must be "arm,idle-state".

	- local-timer-stop
		Usage: See definition
		Value type: <none>
		Definition: if present the CPU local timer control logic is
			    lost on state entry, otherwise it is retained.

	- entry-latency-us
		Usage: Required
		Value type: <prop-encoded-array>
		Definition: u32 value representing worst case latency in
			    microseconds required to enter the idle state.
			    The exit-latency-us duration may be guaranteed
			    only after entry-latency-us has passed.

	- exit-latency-us
		Usage: Required
		Value type: <prop-encoded-array>
		Definition: u32 value representing worst case latency
			    in microseconds required to exit the idle state.

	- min-residency-us
		Usage: Required
		Value type: <prop-encoded-array>
		Definition: u32 value representing minimum residency duration
			    in microseconds, inclusive of preparation and
			    entry, for this idle state to be considered
			    worthwhile energy wise (refer to section 2 of
			    this document for a complete description).

	- wakeup-latency-us:
		Usage: Optional
		Value type: <prop-encoded-array>
		Definition: u32 value representing maximum delay between the
			    signaling of a wake-up event and the CPU being
			    able to execute normal code again. If omitted,
			    this is assumed to be equal to:

				entry-latency-us + exit-latency-us

			    It is important to supply this value on systems
			    where the duration of PREP phase (see diagram 1,
			    section 2) is non-neglibigle.
			    In such systems entry-latency-us + exit-latency-us
			    will exceed wakeup-latency-us by this duration.

	- status:
		Usage: Optional
		Value type: <string>
		Definition: A standard device tree property [5] that indicates
			    the operational status of an idle-state.
			    If present, it shall be:
			    "okay": to indicate that the idle state is
				    operational.
			    "disabled": to indicate that the idle state has
					been disabled in firmware so it is not
					operational.
			    If the property is not present the idle-state must
			    be considered operational.

	- idle-state-name:
		Usage: Optional
		Value type: <string>
		Definition: A string used as a descriptive name for the idle
			    state.

	In addition to the properties listed above, a state node may require
	additional properties specifics to the entry-method defined in the
	idle-states node, please refer to the entry-method bindings
	documentation for properties definitions.

===========================================
4 - Examples
===========================================

Example 1 (ARM 64-bit, 16-cpu system, PSCI enable-method):

cpus {
	#size-cells = <0>;
	#address-cells = <2>;

	CPU0: cpu@0 {
		device_type = "cpu";
		compatible = "arm,cortex-a57";
		reg = <0x0 0x0>;
		enable-method = "psci";
		cpu-idle-states = <&CPU_RETENTION_0_0 &CPU_SLEEP_0_0
				   &CLUSTER_RETENTION_0 &CLUSTER_SLEEP_0>;
	};

	CPU1: cpu@1 {
		device_type = "cpu";
		compatible = "arm,cortex-a57";
		reg = <0x0 0x1>;
		enable-method = "psci";
		cpu-idle-states = <&CPU_RETENTION_0_0 &CPU_SLEEP_0_0
				   &CLUSTER_RETENTION_0 &CLUSTER_SLEEP_0>;
	};

	CPU2: cpu@100 {
		device_type = "cpu";
		compatible = "arm,cortex-a57";
		reg = <0x0 0x100>;
		enable-method = "psci";
		cpu-idle-states = <&CPU_RETENTION_0_0 &CPU_SLEEP_0_0
				   &CLUSTER_RETENTION_0 &CLUSTER_SLEEP_0>;
	};

	CPU3: cpu@101 {
		device_type = "cpu";
		compatible = "arm,cortex-a57";
		reg = <0x0 0x101>;
		enable-method = "psci";
		cpu-idle-states = <&CPU_RETENTION_0_0 &CPU_SLEEP_0_0
				   &CLUSTER_RETENTION_0 &CLUSTER_SLEEP_0>;
	};

	CPU4: cpu@10000 {
		device_type = "cpu";
		compatible = "arm,cortex-a57";
		reg = <0x0 0x10000>;
		enable-method = "psci";
		cpu-idle-states = <&CPU_RETENTION_0_0 &CPU_SLEEP_0_0
				   &CLUSTER_RETENTION_0 &CLUSTER_SLEEP_0>;
	};

	CPU5: cpu@10001 {
		device_type = "cpu";
		compatible = "arm,cortex-a57";
		reg = <0x0 0x10001>;
		enable-method = "psci";
		cpu-idle-states = <&CPU_RETENTION_0_0 &CPU_SLEEP_0_0
				   &CLUSTER_RETENTION_0 &CLUSTER_SLEEP_0>;
	};

	CPU6: cpu@10100 {
		device_type = "cpu";
		compatible = "arm,cortex-a57";
		reg = <0x0 0x10100>;
		enable-method = "psci";
		cpu-idle-states = <&CPU_RETENTION_0_0 &CPU_SLEEP_0_0
				   &CLUSTER_RETENTION_0 &CLUSTER_SLEEP_0>;
	};

	CPU7: cpu@10101 {
		device_type = "cpu";
		compatible = "arm,cortex-a57";
		reg = <0x0 0x10101>;
		enable-method = "psci";
		cpu-idle-states = <&CPU_RETENTION_0_0 &CPU_SLEEP_0_0
				   &CLUSTER_RETENTION_0 &CLUSTER_SLEEP_0>;
	};

	CPU8: cpu@100000000 {
		device_type = "cpu";
		compatible = "arm,cortex-a53";
		reg = <0x1 0x0>;
		enable-method = "psci";
		cpu-idle-states = <&CPU_RETENTION_1_0 &CPU_SLEEP_1_0
				   &CLUSTER_RETENTION_1 &CLUSTER_SLEEP_1>;
	};

	CPU9: cpu@100000001 {
		device_type = "cpu";
		compatible = "arm,cortex-a53";
		reg = <0x1 0x1>;
		enable-method = "psci";
		cpu-idle-states = <&CPU_RETENTION_1_0 &CPU_SLEEP_1_0
				   &CLUSTER_RETENTION_1 &CLUSTER_SLEEP_1>;
	};

	CPU10: cpu@100000100 {
		device_type = "cpu";
		compatible = "arm,cortex-a53";
		reg = <0x1 0x100>;
		enable-method = "psci";
		cpu-idle-states = <&CPU_RETENTION_1_0 &CPU_SLEEP_1_0
				   &CLUSTER_RETENTION_1 &CLUSTER_SLEEP_1>;
	};

	CPU11: cpu@100000101 {
		device_type = "cpu";
		compatible = "arm,cortex-a53";
		reg = <0x1 0x101>;
		enable-method = "psci";
		cpu-idle-states = <&CPU_RETENTION_1_0 &CPU_SLEEP_1_0
				   &CLUSTER_RETENTION_1 &CLUSTER_SLEEP_1>;
	};

	CPU12: cpu@100010000 {
		device_type = "cpu";
		compatible = "arm,cortex-a53";
		reg = <0x1 0x10000>;
		enable-method = "psci";
		cpu-idle-states = <&CPU_RETENTION_1_0 &CPU_SLEEP_1_0
				   &CLUSTER_RETENTION_1 &CLUSTER_SLEEP_1>;
	};

	CPU13: cpu@100010001 {
		device_type = "cpu";
		compatible = "arm,cortex-a53";
		reg = <0x1 0x10001>;
		enable-method = "psci";
		cpu-idle-states = <&CPU_RETENTION_1_0 &CPU_SLEEP_1_0
				   &CLUSTER_RETENTION_1 &CLUSTER_SLEEP_1>;
	};

	CPU14: cpu@100010100 {
		device_type = "cpu";
		compatible = "arm,cortex-a53";
		reg = <0x1 0x10100>;
		enable-method = "psci";
		cpu-idle-states = <&CPU_RETENTION_1_0 &CPU_SLEEP_1_0
				   &CLUSTER_RETENTION_1 &CLUSTER_SLEEP_1>;
	};

	CPU15: cpu@100010101 {
		device_type = "cpu";
		compatible = "arm,cortex-a53";
		reg = <0x1 0x10101>;
		enable-method = "psci";
		cpu-idle-states = <&CPU_RETENTION_1_0 &CPU_SLEEP_1_0
				   &CLUSTER_RETENTION_1 &CLUSTER_SLEEP_1>;
	};

	idle-states {
		entry-method = "psci";

		CPU_RETENTION_0_0: cpu-retention-0-0 {
			compatible = "arm,idle-state";
			arm,psci-suspend-param = <0x0010000>;
			entry-latency-us = <20>;
			exit-latency-us = <40>;
			min-residency-us = <80>;
		};

		CLUSTER_RETENTION_0: cluster-retention-0 {
			compatible = "arm,idle-state";
			local-timer-stop;
			arm,psci-suspend-param = <0x1010000>;
			entry-latency-us = <50>;
			exit-latency-us = <100>;
			min-residency-us = <250>;
			wakeup-latency-us = <130>;
		};

		CPU_SLEEP_0_0: cpu-sleep-0-0 {
			compatible = "arm,idle-state";
			local-timer-stop;
			arm,psci-suspend-param = <0x0010000>;
			entry-latency-us = <250>;
			exit-latency-us = <500>;
			min-residency-us = <950>;
		};

		CLUSTER_SLEEP_0: cluster-sleep-0 {
			compatible = "arm,idle-state";
			local-timer-stop;
			arm,psci-suspend-param = <0x1010000>;
			entry-latency-us = <600>;
			exit-latency-us = <1100>;
			min-residency-us = <2700>;
			wakeup-latency-us = <1500>;
		};

		CPU_RETENTION_1_0: cpu-retention-1-0 {
			compatible = "arm,idle-state";
			arm,psci-suspend-param = <0x0010000>;
			entry-latency-us = <20>;
			exit-latency-us = <40>;
			min-residency-us = <90>;
		};

		CLUSTER_RETENTION_1: cluster-retention-1 {
			compatible = "arm,idle-state";
			local-timer-stop;
			arm,psci-suspend-param = <0x1010000>;
			entry-latency-us = <50>;
			exit-latency-us = <100>;
			min-residency-us = <270>;
			wakeup-latency-us = <100>;
		};

		CPU_SLEEP_1_0: cpu-sleep-1-0 {
			compatible = "arm,idle-state";
			local-timer-stop;
			arm,psci-suspend-param = <0x0010000>;
			entry-latency-us = <70>;
			exit-latency-us = <100>;
			min-residency-us = <300>;
			wakeup-latency-us = <150>;
		};

		CLUSTER_SLEEP_1: cluster-sleep-1 {
			compatible = "arm,idle-state";
			local-timer-stop;
			arm,psci-suspend-param = <0x1010000>;
			entry-latency-us = <500>;
			exit-latency-us = <1200>;
			min-residency-us = <3500>;
			wakeup-latency-us = <1300>;
		};
	};

};

Example 2 (ARM 32-bit, 8-cpu system, two clusters):

cpus {
	#size-cells = <0>;
	#address-cells = <1>;

	CPU0: cpu@0 {
		device_type = "cpu";
		compatible = "arm,cortex-a15";
		reg = <0x0>;
		cpu-idle-states = <&CPU_SLEEP_0_0 &CLUSTER_SLEEP_0>;
	};

	CPU1: cpu@1 {
		device_type = "cpu";
		compatible = "arm,cortex-a15";
		reg = <0x1>;
		cpu-idle-states = <&CPU_SLEEP_0_0 &CLUSTER_SLEEP_0>;
	};

	CPU2: cpu@2 {
		device_type = "cpu";
		compatible = "arm,cortex-a15";
		reg = <0x2>;
		cpu-idle-states = <&CPU_SLEEP_0_0 &CLUSTER_SLEEP_0>;
	};

	CPU3: cpu@3 {
		device_type = "cpu";
		compatible = "arm,cortex-a15";
		reg = <0x3>;
		cpu-idle-states = <&CPU_SLEEP_0_0 &CLUSTER_SLEEP_0>;
	};

	CPU4: cpu@100 {
		device_type = "cpu";
		compatible = "arm,cortex-a7";
		reg = <0x100>;
		cpu-idle-states = <&CPU_SLEEP_1_0 &CLUSTER_SLEEP_1>;
	};

	CPU5: cpu@101 {
		device_type = "cpu";
		compatible = "arm,cortex-a7";
		reg = <0x101>;
		cpu-idle-states = <&CPU_SLEEP_1_0 &CLUSTER_SLEEP_1>;
	};

	CPU6: cpu@102 {
		device_type = "cpu";
		compatible = "arm,cortex-a7";
		reg = <0x102>;
		cpu-idle-states = <&CPU_SLEEP_1_0 &CLUSTER_SLEEP_1>;
	};

	CPU7: cpu@103 {
		device_type = "cpu";
		compatible = "arm,cortex-a7";
		reg = <0x103>;
		cpu-idle-states = <&CPU_SLEEP_1_0 &CLUSTER_SLEEP_1>;
	};

	idle-states {
		CPU_SLEEP_0_0: cpu-sleep-0-0 {
			compatible = "arm,idle-state";
			local-timer-stop;
			entry-latency-us = <200>;
			exit-latency-us = <100>;
			min-residency-us = <400>;
			wakeup-latency-us = <250>;
		};

		CLUSTER_SLEEP_0: cluster-sleep-0 {
			compatible = "arm,idle-state";
			local-timer-stop;
			entry-latency-us = <500>;
			exit-latency-us = <1500>;
			min-residency-us = <2500>;
			wakeup-latency-us = <1700>;
		};

		CPU_SLEEP_1_0: cpu-sleep-1-0 {
			compatible = "arm,idle-state";
			local-timer-stop;
			entry-latency-us = <300>;
			exit-latency-us = <500>;
			min-residency-us = <900>;
			wakeup-latency-us = <600>;
		};

		CLUSTER_SLEEP_1: cluster-sleep-1 {
			compatible = "arm,idle-state";
			local-timer-stop;
			entry-latency-us = <800>;
			exit-latency-us = <2000>;
			min-residency-us = <6500>;
			wakeup-latency-us = <2300>;
		};
	};

};

===========================================
5 - References
===========================================

[1] ARM Linux Kernel documentation - CPUs bindings
    Documentation/devicetree/bindings/arm/cpus.yaml

[2] ARM Linux Kernel documentation - PSCI bindings
    Documentation/devicetree/bindings/arm/psci.txt

[3] ARM Server Base System Architecture (SBSA)
    http://infocenter.arm.com/help/index.jsp

[4] ARM Architecture Reference Manuals
    http://infocenter.arm.com/help/index.jsp

[5] Devicetree Specification
    https://www.devicetree.org/specifications/