How to control the GPIO?

Hardware and peripherals
5

Rockchip GPIO has 5 banks, GPIO0~GPIO4, each bank has 32pins, naming as below:

GPIO0_A0 ~ A7 
GPIO0_B0 ~ B7
GPIO0_C0 ~ C7
GPIO0_D0 ~ D7

GPIO1_A0 ~ A7
....
GPIO1_D0 ~ D7

For Rockchip 4.4 kernel, the GPIO number can be calculated as below, take GPIO4_D5(PIN22 on 40PIN GPIO) as an example:

GPIO4_D5 = 32*4 + 8*3 + 5 = 157

To set GPIO4_D5 output

cd /sys/class/gpio
echo 157 > export
cd gpio157
echo out > direction
echo 1 > value     # output high
echo 0 > value     # output low
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