在使用GPIO的时候，有时候不知道GPIO的状态，也不知道在内核中GPIO是否申请成功。
可以通过/sys/kernel/debug/gpio这个文件来查看。这个文件显示了申请成功的GPIO的输入输出状态和电平。
测试情况：
uranus-a63:/sys/kernel/debug # cat gpio
cat gpio
GPIOs 0-255, platform/pio, pio:
gpio-34 (card-pwr-gpios ) out lo
gpio-35 (SPK ) out lo
gpio-36 (sdc0 cd ) in lo
gpio-37 (ilitek-irq-gpio ) in hi
gpio-38 (ilitek-reset-gpio ) out hi
gpio-97 (vibe ) out lo 表示gpio_request函数里的字符串参数
gpio-142 (? ) in lo
gpio-143 (? ) in lo
gpio-144 (? ) in lo
gpio-145 (? ) in lo
gpio-230 (insert_det_gpio ) in hi
gpio-231 (type_det_gpio1 ) in hi
gpio-232 (? ) in lo
gpio-233 (otg_id ) in hi
gpio-235 (edp_pwr_en ) in hi
gpio-236 (bf3005_light_trig ) out lo
GPIOs 352-415, platform/r_pio, r_pio:
gpio-355 (pax,vcc5v_power ) out hi
gpio-356 (pmu_bat_chggreenled_) out lo
gpio-357 (pmu_bat_chgredled_ct) out lo
gpio-360 (? ) out hi
gpio-362 (pax,sp-interrupt ) in lo
gpio-363 (pax,sp-sleep-control) out lo
gpio-364 (pax,sp_status ) in lo
gpio-365 (pax,sp_to_ap_ack ) out lo
gpio-366 (pax,ap_to_sp_prdwn ) out lo
gpio-367 (pax,sp-power ) out hi
gpio-384 (wlan_regon ) out lo
gpio-385 (wlan_hostwake ) in lo
gpio-386 (bt_rst ) out lo
gpio-387 (bt_hostwake ) in lo
gpio-388 (bt_wake ) out lo
gpio-389 (chip_en ) out lo