Understanding SYSFS GPIO number for Xavier NX

[jtlee]

Hello,

When I saw Xavier NX Pinmux Table, I can’t understand sysfs GPIO number.

According from Pinmux Table, GPIO06 is GPIO3_PCC.03.

As I know, Xavier NX GPIO range is below.
sudo grep tegra-gpio /sys/kernel/debug/gpio
gpiochip1: GPIOs 248-287, parent: platform/c2f0000.gpio, tegra-gpio-aon:
gpiochip0: GPIOs 288-511, parent: platform/2200000.gpio, tegra-gpio:

So, I calculated GPIO number from below formula

Linux GPIO number = (base + (8 * port) + pin)
=> 288 + (8 * 28) + 3 = 515

But, this value is over GPIO number range.

What’s the exact sysfs GPIO number for GPIO3_PCC.03?

[JerryChang]

hello jtlee,

may I know which Jetpack release version you’re using?

@jtlee

=> 288 + (8 * 28) + 3 = 515

BTW,
where did you obtain 28?

[edit] revise the erroneous.

you may refer to tegra194-gpio.h for the port index for AON GPIO, which is 2.
so, the calculation formula of GPIO3_PCC.03 should be… (248 + (2 * 8) + 3) = 267

[jtlee]

Hello, JerryChang

Your guessing is right. I’ve just guessed from Jetson Nano.

Anyway, I tried to access sysfs GPIO, but I failed.
When I run “echo 275 > /sys/class/gpio/export”, it showed below message.

-bash: echo: write error: Device or resource busy

If I checking gpiolist via “sudo cat /sys/kernel/debug/gpio”, I can’t find GPIO 275. Attached file is showing result for “sudo cat /sys/kernel/debug/gpio”
gpiolist.txt (8.9 KB)

Jetpack Version is 4.6.1.

I want to access GPIO06 because GPIO06’s SODIMM number is 130 and our custom board is using this pin.

Thank you.

[JerryChang]

@jtlee

-bash: echo: write error: Device or resource busy

hello jtlee,

it mean this pin is occupied.
as you can see in pinmux spreadsheets, this sample usage is [Baseboard CAM MUX Sel].
for example,
$public_sources/kernel_src/hardware/nvidia/platform/t19x/jakku/kernel-dts/common/tegra194-camera-jakku-rbpcv2-imx219.dtsi

#define CAM_I2C_MUX     TEGRA194_AON_GPIO(CC, 3)

for your own product design and use-case,
please update the device tree accordingly to remove this pin definition.
thanks

[jtlee]

Hello JerryChang.

I wonder that GPIO number for PCC.03 is 267.

When I reviewed tegra194-gpio.h, I found below definition.

#define TEGRA194_AON_GPIO_PORT_AA 0
#define TEGRA194_AON_GPIO_PORT_BB 1
#define TEGRA194_AON_GPIO_PORT_CC 2
#define TEGRA194_AON_GPIO_PORT_DD 3
#define TEGRA194_AON_GPIO_PORT_EE 4

And, you mentioned like below.
#define CAM_I2C_MUX TEGRA194_AON_GPIO(CC, 3)

Also, When I run “sudo cat /sys/kernel/debug/gpio”, I found below.
gpio-267 ( |i2c-mux-gpio ) out hi

So, I guessed that GPIO3_PCC.03 is 248 + (2 * 8) + 3 = 267.

Please confirm it.

Thank you.

[JerryChang]

my bad, I misread the port index of CC. you’re correct that GPIO3_PCC.03 is 248 + (2 * 8) + 3 = 267.