Abhishek Chr

Thanks @Gunjan Gupta.
 
I get following output:

a@bananapicm4io:~$ sudo cat /sys/kernel/debug/pinctrl/ff634400.bus:pinctrl@40-pinctrl-meson/pinmux-pins
Pinmux settings per pin
Format: pin (name): mux_owner gpio_owner hog?
pin 0 (GPIOZ_0): ff3f0000.ethernet (GPIO UNCLAIMED) function eth group eth_mdio
pin 1 (GPIOZ_1): ff3f0000.ethernet (GPIO UNCLAIMED) function eth group eth_mdc
pin 2 (GPIOZ_2): ff3f0000.ethernet (GPIO UNCLAIMED) function eth group eth_rgmii_rx_clk
pin 3 (GPIOZ_3): ff3f0000.ethernet (GPIO UNCLAIMED) function eth group eth_rx_dv
pin 4 (GPIOZ_4): ff3f0000.ethernet (GPIO UNCLAIMED) function eth group eth_rxd0
pin 5 (GPIOZ_5): ff3f0000.ethernet (GPIO UNCLAIMED) function eth group eth_rxd1
pin 6 (GPIOZ_6): ff3f0000.ethernet periphs-banks:518 function eth group eth_rxd2_rgmii
pin 7 (GPIOZ_7): ff3f0000.ethernet (GPIO UNCLAIMED) function eth group eth_rxd3_rgmii
pin 8 (GPIOZ_8): ff3f0000.ethernet (GPIO UNCLAIMED) function eth group eth_rgmii_tx_clk
pin 9 (GPIOZ_9): ff3f0000.ethernet (GPIO UNCLAIMED) function eth group eth_txen
pin 10 (GPIOZ_10): ff3f0000.ethernet (GPIO UNCLAIMED) function eth group eth_txd0
pin 11 (GPIOZ_11): ff3f0000.ethernet (GPIO UNCLAIMED) function eth group eth_txd1
pin 12 (GPIOZ_12): ff3f0000.ethernet (GPIO UNCLAIMED) function eth group eth_txd2_rgmii
pin 13 (GPIOZ_13): ff3f0000.ethernet (GPIO UNCLAIMED) function eth group eth_txd3_rgmii
pin 14 (GPIOZ_14): (MUX UNCLAIMED) (GPIO UNCLAIMED)
pin 15 (GPIOZ_15): (MUX UNCLAIMED) (GPIO UNCLAIMED)
pin 16 (GPIOH_0): ff600000.hdmi-tx (GPIO UNCLAIMED) function hdmitx group hdmitx_sda
pin 17 (GPIOH_1): ff600000.hdmi-tx (GPIO UNCLAIMED) function hdmitx group hdmitx_sck
pin 18 (GPIOH_2): ff600000.hdmi-tx (GPIO UNCLAIMED) function hdmitx group hdmitx_hpd_in
pin 19 (GPIOH_3): ff800280.cec (GPIO UNCLAIMED) function cec_ao_b_h group cec_ao_b_h
pin 20 (GPIOH_4): (MUX UNCLAIMED) (GPIO UNCLAIMED)
pin 21 (GPIOH_5): (MUX UNCLAIMED) (GPIO UNCLAIMED)
pin 22 (GPIOH_6): ffd1e000.i2c (GPIO UNCLAIMED) function i2c1 group i2c1_sda_h6
pin 23 (GPIOH_7): ffd1e000.i2c (GPIO UNCLAIMED) function i2c1 group i2c1_sck_h7
pin 24 (GPIOH_8): (MUX UNCLAIMED) (GPIO UNCLAIMED)
pin 25 (BOOT_0): ffe07000.mmc (GPIO UNCLAIMED) function emmc group emmc_nand_d0
pin 26 (BOOT_1): ffe07000.mmc (GPIO UNCLAIMED) function emmc group emmc_nand_d1
pin 27 (BOOT_2): ffe07000.mmc (GPIO UNCLAIMED) function emmc group emmc_nand_d2
pin 28 (BOOT_3): ffe07000.mmc (GPIO UNCLAIMED) function emmc group emmc_nand_d3
pin 29 (BOOT_4): ffe07000.mmc (GPIO UNCLAIMED) function emmc group emmc_nand_d4
pin 30 (BOOT_5): ffe07000.mmc (GPIO UNCLAIMED) function emmc group emmc_nand_d5
pin 31 (BOOT_6): ffe07000.mmc (GPIO UNCLAIMED) function emmc group emmc_nand_d6
pin 32 (BOOT_7): ffe07000.mmc (GPIO UNCLAIMED) function emmc group emmc_nand_d7
pin 33 (BOOT_8): ffe07000.mmc (GPIO UNCLAIMED) function emmc group emmc_clk
pin 34 (BOOT_9): (MUX UNCLAIMED) (GPIO UNCLAIMED)
pin 35 (BOOT_10): ffe07000.mmc (GPIO UNCLAIMED) function emmc group emmc_cmd
pin 36 (BOOT_11): (MUX UNCLAIMED) (GPIO UNCLAIMED)
pin 37 (BOOT_12): (MUX UNCLAIMED) periphs-banks:549
pin 38 (BOOT_13): ffe07000.mmc (GPIO UNCLAIMED) function emmc group emmc_nand_ds
pin 39 (BOOT_14): (MUX UNCLAIMED) (GPIO UNCLAIMED)
pin 40 (BOOT_15): (MUX UNCLAIMED) (GPIO UNCLAIMED)
pin 41 (GPIOC_0): (MUX UNCLAIMED) (GPIO UNCLAIMED)
pin 42 (GPIOC_1): (MUX UNCLAIMED) (GPIO UNCLAIMED)
pin 43 (GPIOC_2): (MUX UNCLAIMED) (GPIO UNCLAIMED)
pin 44 (GPIOC_3): (MUX UNCLAIMED) (GPIO UNCLAIMED)
pin 45 (GPIOC_4): ffe05000.mmc (GPIO UNCLAIMED) function gpio_periphs group GPIOC_4
pin 46 (GPIOC_5): (MUX UNCLAIMED) (GPIO UNCLAIMED)
pin 47 (GPIOC_6): (MUX UNCLAIMED) periphs-banks:559
pin 48 (GPIOC_7): (MUX UNCLAIMED) (GPIO UNCLAIMED)
pin 49 (GPIOA_0): (MUX UNCLAIMED) (GPIO UNCLAIMED)
pin 50 (GPIOA_1): (MUX UNCLAIMED) (GPIO UNCLAIMED)
pin 51 (GPIOA_2): (MUX UNCLAIMED) (GPIO UNCLAIMED)
pin 52 (GPIOA_3): (MUX UNCLAIMED) (GPIO UNCLAIMED)
pin 53 (GPIOA_4): (MUX UNCLAIMED) (GPIO UNCLAIMED)
pin 54 (GPIOA_5): (MUX UNCLAIMED) (GPIO UNCLAIMED)
pin 55 (GPIOA_6): (MUX UNCLAIMED) (GPIO UNCLAIMED)
pin 56 (GPIOA_7): (MUX UNCLAIMED) (GPIO UNCLAIMED)
pin 57 (GPIOA_8): (MUX UNCLAIMED) periphs-banks:569
pin 58 (GPIOA_9): (MUX UNCLAIMED) (GPIO UNCLAIMED)
pin 59 (GPIOA_10): (MUX UNCLAIMED) (GPIO UNCLAIMED)
pin 60 (GPIOA_11): (MUX UNCLAIMED) (GPIO UNCLAIMED)
pin 61 (GPIOA_12): (MUX UNCLAIMED) (GPIO UNCLAIMED)
pin 62 (GPIOA_13): (MUX UNCLAIMED) (GPIO UNCLAIMED)
pin 63 (GPIOA_14): ffd1c000.i2c (GPIO UNCLAIMED) function i2c3 group i2c3_sda_a
pin 64 (GPIOA_15): ffd1c000.i2c (GPIO UNCLAIMED) function i2c3 group i2c3_sck_a
pin 65 (GPIOX_0): ffe03000.mmc (GPIO UNCLAIMED) function sdio group sdio_d0
pin 66 (GPIOX_1): ffe03000.mmc (GPIO UNCLAIMED) function sdio group sdio_d1
pin 67 (GPIOX_2): ffe03000.mmc (GPIO UNCLAIMED) function sdio group sdio_d2
pin 68 (GPIOX_3): ffe03000.mmc (GPIO UNCLAIMED) function sdio group sdio_d3
pin 69 (GPIOX_4): ffe03000.mmc (GPIO UNCLAIMED) function sdio group sdio_clk
pin 70 (GPIOX_5): ffe03000.mmc (GPIO UNCLAIMED) function sdio group sdio_cmd
pin 71 (GPIOX_6): (MUX UNCLAIMED) (GPIO UNCLAIMED)
pin 72 (GPIOX_7): (MUX UNCLAIMED) (GPIO UNCLAIMED)
pin 73 (GPIOX_8): (MUX UNCLAIMED) (GPIO UNCLAIMED)
pin 74 (GPIOX_9): (MUX UNCLAIMED) (GPIO UNCLAIMED)
pin 75 (GPIOX_10): (MUX UNCLAIMED) (GPIO UNCLAIMED)
pin 76 (GPIOX_11): (MUX UNCLAIMED) (GPIO UNCLAIMED)
pin 77 (GPIOX_12): ffd24000.serial (GPIO UNCLAIMED) function uart_a group uart_a_tx
pin 78 (GPIOX_13): ffd24000.serial (GPIO UNCLAIMED) function uart_a group uart_a_rx
pin 79 (GPIOX_14): ffd24000.serial (GPIO UNCLAIMED) function uart_a group uart_a_cts
pin 80 (GPIOX_15): ffd24000.serial (GPIO UNCLAIMED) function uart_a group uart_a_rts
pin 81 (GPIOX_16): ffd19000.pwm (GPIO UNCLAIMED) function pwm_e group pwm_e
pin 82 (GPIOX_17): (MUX UNCLAIMED) (GPIO UNCLAIMED)
pin 83 (GPIOX_18): (MUX UNCLAIMED) periphs-banks:595
pin 84 (GPIOX_19): (MUX UNCLAIMED) periphs-banks:596
 
So my GPIOX_18 pin number is 595