1# Copyright (c) 2022 Espressif Systems (Shanghai) Co., Ltd.
2# SPDX-License-Identifier: Apache-2.0
3
4description: |
5    Espressif's pin controller is in charge of controlling pin configurations, pin
6    functionalities and pin properties as defined by pin states. In its turn, pin
7    states are composed by groups of pre-defined pin muxing definitions and user
8    provided pin properties.
9
10    Each Zephyr-based application has its own set of pin muxing/pin configuration
11    requirements. The next steps use ESP-WROVER-KIT's I2C_0 to illustrate how one
12    could change a node's pin state properties. Though based on a particular board,
13    the same steps can be tweaked to address specifics of any other target board.
14
15    Suppose an application running on top of the ESP-WROVER-KIT board, for some
16    reason it needs I2C_0's SDA signal to be routed to GPIO_33. When looking at
17    that board's original device tree source file (i.e., 'esp_wrover_kit.dts'),
18    you'll notice that the I2C_0 node is already assigned to a pre-defined state.
19    Below is highlighted the information that most interests us on that file
20
21
22        #include "esp_wrover_kit-pinctrl.dtsi"
23
24        &i2c0 {
25                ...
26                pinctrl-0 = <&i2c0_default>;
27                pinctrl-names = "default";
28        };
29
30
31    From the above excerpt, the pincrl-0 property is assigned the 'i2c0_default'
32    state value. This and other pin states of the board are defined on another file
33    (in this case, 'esp_wrover_kit-pinctrl.dtsi') on the same folder of the DTS file.
34    Check below the excerpt describing I2C_0's default state on that file
35
36
37        i2c0_default: i2c0_default {
38                group1 {
39                        pinmux = <I2C0_SDA_GPIO21>,
40                                 <I2C0_SCL_GPIO22>;
41                        bias-pull-up;
42                        drive-open-drain;
43                        output-high;
44                };
45        };
46
47
48    Only the 'pinmux' property above is actually required, other properties can
49    be chosen if meaningful for the target application and, of course, supported
50    by your target hardware. For example, some custom board may have an external
51    pull-up resistor soldered to GPIO_21's pin pad, in which case, 'bias-pull-up'
52    could be no longer required.
53
54    Back to our fictional application, the previous I2C_0 state definition does not
55    meet our expectations as we would like to route I2C_0's SDA signal to GPIO_33
56    instead of to GPIO_21. To achieve it, we need to update the 'pinmux' property
57    accordingly.
58
59    Note that replacing 'I2C0_SDA_GPIO21' by 'I2C0_SDA_GPIO33' is very tempting and
60    may even work, however, unless you have checked the hardware documentation first,
61    it is not recommended. That's because there are no guarantees that a particular
62    IO pin has the capability to route any specific signal.
63
64    The recommendation is to check the pinmux macros definitions available for the
65    target SoC in the following URL
66
67
68    https://github.com/zephyrproject-rtos/hal_espressif/tree/zephyr/include/dt-bindings/pinctrl
69
70
71    The ESP-WROVER-KIT board is based on the ESP32 SoC, in that case, we search
72    through the file 'esp32-pinctrl.h' in the above URL. Luckily for us, there is
73    one definition on that file that corresponds to our needs
74
75
76        #define I2C0_SDA_GPIO33 \
77                ESP32_PINMUX(33, ESP_I2CEXT0_SDA_IN, ESP_I2CEXT0_SDA_OUT)
78
79
80    Now, we go back to edit 'esp_wrover_kit-pinctrl.dtsi' and create a new pin state
81    on that file (or replace/update the one already defined) using the pinmux macro
82    definition above, yielding
83
84
85        i2c0_default: i2c0_default {
86                group1 {
87                        pinmux = <I2C0_SDA_GPIO33>,
88                                 <I2C0_SCL_GPIO22>;
89                        bias-pull-up;
90                        drive-open-drain;
91                        output-high;
92                };
93        };
94
95
96    With proper modifications, the same steps above apply when using different
97    combinations of boards, SoCs, peripherals and peripheral pins.
98
99    Note: Not all pins are available for a given peripheral, it depends if that
100          pin supports a set of properties required by the target peripheral.
101
102          When defining a state, the pin muxing information is constrained to
103          the definitions at 'hal_espressif', however, pin properties (like
104          bias-push-pull, drive-open-drain, etc) can be freely chosen, given the
105          property is meaningful to the peripheral signal and that it is also
106          available in the target GPIO.
107
108          Another thing worth noting is that all pin properties should be grouped.
109          All pins sharing common properties go under a common group (in the above
110          example, all pins are in 'group1'). Other peripherals can have more than
111          one group.
112
113compatible: "espressif,esp32-pinctrl"
114
115include: base.yaml
116
117child-binding:
118  description: |
119    Espressif pin controller pin configuration state nodes.
120  child-binding:
121    description:
122      Espressif pin controller pin configuration group.
123
124    include:
125      - name: pincfg-node.yaml
126        property-allowlist:
127          - bias-disable
128          - bias-pull-down
129          - bias-pull-up
130          - drive-push-pull
131          - drive-open-drain
132          - input-enable
133          - output-enable
134          - output-high
135          - output-low
136
137    properties:
138      pinmux:
139        required: true
140        type: array
141        description: |
142          Each array element represents pin muxing information of an individual
143          pin. The array elements are pre-declared macros taken from Espressif's
144          HAL.
145