xref: /linux/Documentation/driver-api/thermal/exynos_thermal_emulation.rst (revision 976e3645923bdd2fe7893aae33fd7a21098bfb28) 
1=====================
2Exynos Emulation Mode
3=====================
4
5Copyright (C) 2012 Samsung Electronics
6
7Written by Jonghwa Lee <jonghwa3.lee@samsung.com>
8
9Description
10-----------
11
12Exynos 4x12 (4212, 4412) and 5 series provide emulation mode for thermal
13management unit. Thermal emulation mode supports software debug for
14TMU's operation. User can set temperature manually with software code
15and TMU will read current temperature from user value not from sensor's
16value.
17
18Enabling CONFIG_THERMAL_EMULATION option will make this support
19available. When it's enabled, sysfs node will be created as
20/sys/devices/virtual/thermal/thermal_zone'zone id'/emul_temp.
21
22The sysfs node, 'emul_node', will contain value 0 for the initial state.
23When you input any temperature you want to update to sysfs node, it
24automatically enable emulation mode and current temperature will be
25changed into it.
26
27(Exynos also supports user changeable delay time which would be used to
28delay of changing temperature. However, this node only uses same delay
29of real sensing time, 938us.)
30
31Exynos emulation mode requires synchronous of value changing and
32enabling. It means when you want to update the any value of delay or
33next temperature, then you have to enable emulation mode at the same
34time. (Or you have to keep the mode enabling.) If you don't, it fails to
35change the value to updated one and just use last succeessful value
36repeatedly. That's why this node gives users the right to change
37termerpature only. Just one interface makes it more simply to use.
38
39Disabling emulation mode only requires writing value 0 to sysfs node.
40
41::
42
43
44  TEMP	120 |
45	    |
46	100 |
47	    |
48	 80 |
49	    |				 +-----------
50	 60 |      			 |	    |
51	    |		   +-------------|          |
52	 40 |              |         	 |          |
53	    |		   |		 |          |
54	 20 |		   |		 |          +----------
55	    |		   |		 |          |          |
56	  0 |______________|_____________|__________|__________|_________
57		   A		 A	    A		       A     TIME
58		   |<----->|	 |<----->|  |<----->|	       |
59		   | 938us |  	 |	 |  |       |          |
60  emulation   : 0  50	   |  	 70      |  20      |          0
61  current temp:   sensor   50		 70         20	      sensor
62