1 ==============================================
2 rotary-encoder - a generic driver for GPIO con
3 ==============================================
4
5 :Author: Daniel Mack <daniel@caiaq.de>, Feb 200
6
7 Function
8 --------
9
10 Rotary encoders are devices which are connecte
11 peripherals with two wires. The outputs are ph
12 and by triggering on falling and rising edges,
13 be determined.
14
15 Some encoders have both outputs low in stable
16 a stable state with both outputs high (half-pe
17 a stable state in all steps (quarter-period mo
18
19 The phase diagram of these two outputs look li
20
21 _____ _____ ____
22 | | | | |
23 Channel A ____| |_____| |_____|
24
25 : : : : : : : : : :
26 __ _____ _____ _
27 | | | | | |
28 Channel B |_____| |_____| |_____|
29
30 : : : : : : : : : :
31 Event a b c d a b c d a b
32
33 |<-------->|
34 one step
35
36 |<-->|
37 one step (half-period mode)
38
39 |<>|
40 one step (quarter-period mod
41
42 For more information, please see
43 https://en.wikipedia.org/wiki/Rotary_e
44
45
46 Events / state machine
47 ----------------------
48
49 In half-period mode, state a) and c) above are
50 rotational direction based on the last stable
51 states b) and d) given that the new stable sta
52 (i.e. the rotation was not reversed half-way).
53
54 Otherwise, the following apply:
55
56 a) Rising edge on channel A, channel B in low
57 This state is used to recognize a cloc
58
59 b) Rising edge on channel B, channel A in high
60 When entering this state, the encoder
61 meaning that there it has seen half th
62
63 c) Falling edge on channel A, channel B in hig
64 This state is used to recognize a coun
65
66 d) Falling edge on channel B, channel A in low
67 Parking position. If the encoder enter
68 should have happened, unless it flippe
69 'armed' state tells us about that.
70
71 Platform requirements
72 ---------------------
73
74 As there is no hardware dependent call in this
75 used with must support gpiolib. Another requir
76 able to fire on both edges.
77
78
79 Board integration
80 -----------------
81
82 To use this driver in your system, register a
83 name 'rotary-encoder' and associate the IRQs a
84 data with it. Because the driver uses generic
85 be done either via device tree, ACPI, or using
86 example below:
87
88 ::
89
90 /* board support file example */
91
92 #include <linux/input.h>
93 #include <linux/gpio/machine.h>
94 #include <linux/property.h>
95
96 #define GPIO_ROTARY_A 1
97 #define GPIO_ROTARY_B 2
98
99 static struct gpiod_lookup_table rotar
100 .dev_id = "rotary-encoder.0",
101 .table = {
102 GPIO_LOOKUP_IDX("gpio-
103 GPIO_R
104 GPIO_LOOKUP_IDX("gpio-
105 GPIO_R
106 { },
107 },
108 };
109
110 static const struct property_entry rot
111 PROPERTY_ENTRY_U32("rotary-enc
112 PROPERTY_ENTRY_U32("linux,axis
113 PROPERTY_ENTRY_U32("rotary-enc
114 { },
115 };
116
117 static const struct software_node rota
118 .properties = rotary_encoder_p
119 };
120
121 static struct platform_device rotary_e
122 .name = "rotary-enco
123 .id = 0,
124 };
125
126 ...
127
128 gpiod_add_lookup_table(&rotary_encoder
129 device_add_software_node(&rotary_encod
130 platform_device_register(&rotary_encod
131
132 ...
133
134 Please consult device tree binding documentati
135 supported by the driver.
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