An example where we configure imx8mp GPIO1_IO15 (B5) to use as a PWM output.
Can configure it in several ways in the device-tree.
option 1
&pwm4 {
status = "okay";
};
&iomuxc {
pinctrl-names = "default";
pinctrl-0 = <&..>, <&pinctrl_pwm4>; // other pinctrls and pinctrl_pwm4
pinctrl_pwm4: pwm4grp {
fsl,pins = <
MX8MP_IOMUXC_GPIO1_IO15__PWM4_OUT 0x00000006
>;
};
};
option 2
&pwm4 {
pinctrl-names = "default";
pinctrl-0 = <&pinctrl_pwm4>;
status = "okay";
};
&iomuxc {
pinctrl-names = "default";
pinctrl-0 = <&..>; // other pinctrls but no pinctrl_pwm4
pinctrl_pwm4: pwm4grp {
fsl,pins = <
MX8MP_IOMUXC_GPIO1_IO15__PWM4_OUT 0x00000006
>;
};
};
Documentation/devicetree/bindings/pinctrl/fsl,imx8mp-pinctrl.yaml tells us how to interpret the pinmux settings we are seeing in the device-tree
fsl,pins:
description:
each entry consists of 6 integers and represents the mux and config
setting for one pin. The first 5 integers <mux_reg conf_reg input_reg
mux_val input_val> are specified using a PIN_FUNC_ID macro, which can
be found in <arch/arm64/boot/dts/freescale/imx8mp-pinfunc.h>. The last
integer CONFIG is the pad setting value like pull-up on this pin. Please
refer to i.MX8M Plus Reference Manual for detailed CONFIG settings.
$ref: /schemas/types.yaml#/definitions/uint32-matrix
items:
items:
- description: |
"mux_reg" indicates the offset of mux register.
- description: |
"conf_reg" indicates the offset of pad configuration register.
- description: |
"input_reg" indicates the offset of select input register.
- description: |
"mux_val" indicates the mux value to be applied.
- description: |
"input_val" indicates the select input value to be applied.
- description: |
"pad_setting" indicates the pad configuration value to be applied..
from arch/arm64/boot/dts/freescale/imx8mp-pinfunc.h
pad/pin functionality we want to
in imx8mp assign to the pad
|--------| |---------|
#define MX8MP_IOMUXC_GPIO1_IO15__GPIO1_IO15 0x050 0x2B0 0x000 0x0 0x0
#define MX8MP_IOMUXC_GPIO1_IO15__USB2_OC 0x050 0x2B0 0x000 0x1 0x0
#define MX8MP_IOMUXC_GPIO1_IO15__USDHC3_WP 0x050 0x2B0 0x634 0x4 0x0
#define MX8MP_IOMUXC_GPIO1_IO15__PWM4_OUT 0x050 0x2B0 0x000 0x5 0x0
#define MX8MP_IOMUXC_GPIO1_IO15__CCM_CLKO2 0x050 0x2B0 0x000 0x6 0x0
pin mux from the imx8mp reference manual
instance port pad mode
CCM CCM_CLKO2 GPIO1_IO15 ALT6
GPIO1 GPIO1_IO15 GPIO1_IO15 ALT0
PWM4 PWM4_OUT GPIO1_IO15 ALT5
USB2 USB2_OC GPIO1_IO15 ALT1
USDHC3 USDHC3_WP GPIO1_IO15 ALT4
from the imx8mp reference manual, we see mux_reg and conf_reg registers of iomuxc are
32-bit MUX Control Register IOMUXC_SW_MUX_CTL_PAD_x to configure ALT mode (MUX MODE)
32-bit PAD Control Register IOMUXC_SW_PAD_CTL_PAD_x to configure pad settings
for our GPIO1_IO15
SW_MUX_CTL_PAD_GPIO1_IO15 SW MUX Control Register
(IOMUXC_SW_MUX_CTL_PAD_GPIO1_IO15)
Address: 3033_0000h base + 50h offset = 3033_0050h
31 .... 5 4 3 2 1 0
[reserved][SION][reserved][mux mode]
mux_val: IOMUXC_SW_MUX_CTL_PAD_GPIO1_IO15[2:0] = 101 - ALT5_PWM4_OUT
SW_PAD_CTL_PAD_GPIO1_IO15 SW PAD Control Register
(IOMUXC_SW_PAD_CTL_PAD_GPIO1_IO15)
Address: 3033_0000h base + 2B0h offset = 3033_02B0h
31 .... 9 8 7 6 5 4 3 2..1 0
[reserved][PE][HYS][PUE][ODE][FSEL][reserved][DSE][reserved]
pad_setting = 0x00000006 : sets the drive strength
where
PE : pull resistors enable/disable
HYS : cmos/schmitt
PUE : pull up/down config
ODE : open drain enable/disable
FSEL: slew rate slow/fast
DSE : drive strength
Other than linux kernel documentation, some good documentation on pin setting can be found in
AN5078: Influence of Pin Setting on System Function and Performance