brock@uncacsci-pi3-d:~$ cd /sys/bus
brock@uncacsci-pi3-d:/sys/bus$ ls
amba         container     gpio  iscsi_flashnode  platform  spi
clockevents  cpu           hid   mipi-dsi         scsi      usb
clocksource  event_source  i2c   mmc              sdio      workqueue
brock@uncacsci-pi3-d:/sys/bus$ cd /sys/bug/gpio
bash: cd: /sys/bug/gpio: No such file or directory
brock@uncacsci-pi3-d:/sys/bus$ ls -l
total 0
drwxr-xr-x 4 root root 0 Dec 31  1969 amba
drwxr-xr-x 4 root root 0 Dec 31  1969 clockevents
drwxr-xr-x 4 root root 0 Dec 31  1969 clocksource
drwxr-xr-x 4 root root 0 Dec 31  1969 container
drwxr-xr-x 4 root root 0 Dec 31  1969 cpu
drwxr-xr-x 4 root root 0 Dec 31  1969 event_source
drwxr-xr-x 4 root root 0 Dec 31  1969 gpio
drwxr-xr-x 4 root root 0 Dec 31  1969 hid
drwxr-xr-x 4 root root 0 Dec 31  1969 i2c
drwxr-xr-x 4 root root 0 Dec 31  1969 iscsi_flashnode
drwxr-xr-x 4 root root 0 Dec 31  1969 mipi-dsi
drwxr-xr-x 4 root root 0 Dec 31  1969 mmc
drwxr-xr-x 4 root root 0 Dec 31  1969 platform
drwxr-xr-x 4 root root 0 Dec 31  1969 scsi
drwxr-xr-x 4 root root 0 Dec 31  1969 sdio
drwxr-xr-x 4 root root 0 Dec 31  1969 spi
drwxr-xr-x 4 root root 0 Dec 31  1969 usb
drwxr-xr-x 4 root root 0 Dec 31  1969 workqueue
brock@uncacsci-pi3-d:/sys/bus$ ls -l /dev
total 0
crw------- 1 root root     10, 235 Feb  2 19:32 autofs
drwxr-xr-x 2 root root         600 Feb  2 19:32 block
crw------- 1 root root     10, 234 Feb  2 19:32 btrfs-control
drwxr-xr-x 3 root root          60 Dec 31  1969 bus
crw------- 1 root root     10,  63 Feb  2 19:32 cachefiles
drwxr-xr-x 2 root root        2480 Feb  2 19:32 char
crw------- 1 root root      5,   1 Feb  2 19:32 console
crw------- 1 root root     10,  62 Feb  2 19:32 cpu_dma_latency
crw------- 1 root root     10, 203 Feb  2 19:32 cuse
drwxr-xr-x 7 root root         140 Feb  2 19:32 disk
crw-rw---- 1 root video    29,   0 Feb  2 19:32 fb0
lrwxrwxrwx 1 root root          13 Dec 31  1969 fd -> /proc/self/fd
crw-rw-rw- 1 root root      1,   7 Feb  2 19:32 full
crw-rw-rw- 1 root root     10, 229 Feb  2 19:32 fuse
crw------- 1 root root    254,   0 Feb  2 19:32 gpiochip0
crw------- 1 root root    254,   1 Feb  2 19:32 gpiochip1
crw------- 1 root root    254,   2 Feb  2 19:32 gpiochip2
crw-rw---- 1 root gpio    243,   0 Feb  2 19:32 gpiomem
crw------- 1 root root     10, 183 Feb  2 19:32 hwrng
crw-rw---- 1 root i2c      89,   1 Feb  2 19:32 i2c-1
lrwxrwxrwx 1 root root          25 Dec 31  1969 initctl -> /run/systemd/initctl/fifo
drwxr-xr-x 2 root root          60 Dec 31  1969 input
crw-r--r-- 1 root root      1,  11 Feb  2 19:32 kmsg
lrwxrwxrwx 1 root root          28 Dec 31  1969 log -> /run/systemd/journal/dev-log
brw-rw---- 1 root disk      7,   0 Feb  2 19:32 loop0
brw-rw---- 1 root disk      7,   1 Feb  2 19:32 loop1
brw-rw---- 1 root disk      7,   2 Feb  2 19:32 loop2
brw-rw---- 1 root disk      7,   3 Feb  2 19:32 loop3
brw-rw---- 1 root disk      7,   4 Feb  2 19:32 loop4
brw-rw---- 1 root disk      7,   5 Feb  2 19:32 loop5
brw-rw---- 1 root disk      7,   6 Feb  2 19:32 loop6
brw-rw---- 1 root disk      7,   7 Feb  2 19:32 loop7
crw-rw---- 1 root disk     10, 237 Feb  2 19:32 loop-control
drwxr-xr-x 2 root root          60 Feb  2 19:32 mapper
crw-r----- 1 root kmem      1,   1 Feb  2 19:32 mem
crw------- 1 root root     10,  59 Feb  2 19:32 memory_bandwidth
brw-rw---- 1 root disk    179,   0 Feb  2 19:32 mmcblk0
brw-rw---- 1 root disk    179,   1 Feb  2 19:32 mmcblk0p1
brw-rw---- 1 root disk    179,   2 Feb  2 19:32 mmcblk0p2
brw-rw---- 1 root disk    179,   3 Feb  2 19:32 mmcblk0p3
drwxrwxrwt 2 root root          40 Dec 31  1969 mqueue
drwxr-xr-x 2 root root          60 Feb  2 19:32 net
crw------- 1 root root     10,  61 Feb  2 19:32 network_latency
crw------- 1 root root     10,  60 Feb  2 19:32 network_throughput
crw-rw-rw- 1 root root      1,   3 Feb  2 19:32 null
crw------- 1 root root    108,   0 Feb  2 19:32 ppp
crw-rw-rw- 1 root tty       5,   2 Feb  2 20:58 ptmx
drwxr-xr-x 2 root root           0 Dec 31  1969 pts
brw-rw---- 1 root disk      1,   0 Feb  2 19:32 ram0
brw-rw---- 1 root disk      1,   1 Feb  2 19:32 ram1
brw-rw---- 1 root disk      1,  10 Feb  2 19:32 ram10
brw-rw---- 1 root disk      1,  11 Feb  2 19:32 ram11
brw-rw---- 1 root disk      1,  12 Feb  2 19:32 ram12
brw-rw---- 1 root disk      1,  13 Feb  2 19:32 ram13
brw-rw---- 1 root disk      1,  14 Feb  2 19:32 ram14
brw-rw---- 1 root disk      1,  15 Feb  2 19:32 ram15
brw-rw---- 1 root disk      1,   2 Feb  2 19:32 ram2
brw-rw---- 1 root disk      1,   3 Feb  2 19:32 ram3
brw-rw---- 1 root disk      1,   4 Feb  2 19:32 ram4
brw-rw---- 1 root disk      1,   5 Feb  2 19:32 ram5
brw-rw---- 1 root disk      1,   6 Feb  2 19:32 ram6
brw-rw---- 1 root disk      1,   7 Feb  2 19:32 ram7
brw-rw---- 1 root disk      1,   8 Feb  2 19:32 ram8
brw-rw---- 1 root disk      1,   9 Feb  2 19:32 ram9
crw-rw-rw- 1 root root      1,   8 Feb  2 19:32 random
drwxr-xr-x 2 root root          60 Dec 31  1969 raw
crw-rw-r-- 1 root root     10,  58 Feb  2 19:32 rfkill
lrwxrwxrwx 1 root root           7 Feb  2 19:32 serial1 -> ttyAMA0
drwxrwxrwt 2 root root          40 Feb  2 19:32 shm
drwxr-xr-x 3 root root         160 Feb  2 19:32 snd
lrwxrwxrwx 1 root root          15 Dec 31  1969 stderr -> /proc/self/fd/2
lrwxrwxrwx 1 root root          15 Dec 31  1969 stdin -> /proc/self/fd/0
lrwxrwxrwx 1 root root          15 Dec 31  1969 stdout -> /proc/self/fd/1
crw-rw-rw- 1 root tty       5,   0 Feb  2 20:58 tty
crw--w---- 1 root tty       4,   0 Feb  2 19:32 tty0
crw--w---- 1 root tty       4,   1 Feb  2 19:32 tty1
crw--w---- 1 root tty       4,  10 Feb  2 19:32 tty10
crw--w---- 1 root tty       4,  11 Feb  2 19:32 tty11
crw--w---- 1 root tty       4,  12 Feb  2 19:32 tty12
crw--w---- 1 root tty       4,  13 Feb  2 19:32 tty13
crw--w---- 1 root tty       4,  14 Feb  2 19:32 tty14
crw--w---- 1 root tty       4,  15 Feb  2 19:32 tty15
crw--w---- 1 root tty       4,  16 Feb  2 19:32 tty16
crw--w---- 1 root tty       4,  17 Feb  2 19:32 tty17
crw--w---- 1 root tty       4,  18 Feb  2 19:32 tty18
crw--w---- 1 root tty       4,  19 Feb  2 19:32 tty19
crw--w---- 1 root tty       4,   2 Feb  2 19:32 tty2
crw--w---- 1 root tty       4,  20 Feb  2 19:32 tty20
crw--w---- 1 root tty       4,  21 Feb  2 19:32 tty21
crw--w---- 1 root tty       4,  22 Feb  2 19:32 tty22
crw--w---- 1 root tty       4,  23 Feb  2 19:32 tty23
crw--w---- 1 root tty       4,  24 Feb  2 19:32 tty24
crw--w---- 1 root tty       4,  25 Feb  2 19:32 tty25
crw--w---- 1 root tty       4,  26 Feb  2 19:32 tty26
crw--w---- 1 root tty       4,  27 Feb  2 19:32 tty27
crw--w---- 1 root tty       4,  28 Feb  2 19:32 tty28
crw--w---- 1 root tty       4,  29 Feb  2 19:32 tty29
crw--w---- 1 root tty       4,   3 Feb  2 19:32 tty3
crw--w---- 1 root tty       4,  30 Feb  2 19:32 tty30
crw--w---- 1 root tty       4,  31 Feb  2 19:32 tty31
crw--w---- 1 root tty       4,  32 Feb  2 19:32 tty32
crw--w---- 1 root tty       4,  33 Feb  2 19:32 tty33
crw--w---- 1 root tty       4,  34 Feb  2 19:32 tty34
crw--w---- 1 root tty       4,  35 Feb  2 19:32 tty35
crw--w---- 1 root tty       4,  36 Feb  2 19:32 tty36
crw--w---- 1 root tty       4,  37 Feb  2 19:32 tty37
crw--w---- 1 root tty       4,  38 Feb  2 19:32 tty38
crw--w---- 1 root tty       4,  39 Feb  2 19:32 tty39
crw--w---- 1 root tty       4,   4 Feb  2 19:32 tty4
crw--w---- 1 root tty       4,  40 Feb  2 19:32 tty40
crw--w---- 1 root tty       4,  41 Feb  2 19:32 tty41
crw--w---- 1 root tty       4,  42 Feb  2 19:32 tty42
crw--w---- 1 root tty       4,  43 Feb  2 19:32 tty43
crw--w---- 1 root tty       4,  44 Feb  2 19:32 tty44
crw--w---- 1 root tty       4,  45 Feb  2 19:32 tty45
crw--w---- 1 root tty       4,  46 Feb  2 19:32 tty46
crw--w---- 1 root tty       4,  47 Feb  2 19:32 tty47
crw--w---- 1 root tty       4,  48 Feb  2 19:32 tty48
crw--w---- 1 root tty       4,  49 Feb  2 19:32 tty49
crw--w---- 1 root tty       4,   5 Feb  2 19:32 tty5
crw--w---- 1 root tty       4,  50 Feb  2 19:32 tty50
crw--w---- 1 root tty       4,  51 Feb  2 19:32 tty51
crw--w---- 1 root tty       4,  52 Feb  2 19:32 tty52
crw--w---- 1 root tty       4,  53 Feb  2 19:32 tty53
crw--w---- 1 root tty       4,  54 Feb  2 19:32 tty54
crw--w---- 1 root tty       4,  55 Feb  2 19:32 tty55
crw--w---- 1 root tty       4,  56 Feb  2 19:32 tty56
crw--w---- 1 root tty       4,  57 Feb  2 19:32 tty57
crw--w---- 1 root tty       4,  58 Feb  2 19:32 tty58
crw--w---- 1 root tty       4,  59 Feb  2 19:32 tty59
crw--w---- 1 root tty       4,   6 Feb  2 19:32 tty6
crw--w---- 1 root tty       4,  60 Feb  2 19:32 tty60
crw--w---- 1 root tty       4,  61 Feb  2 19:32 tty61
crw--w---- 1 root tty       4,  62 Feb  2 19:32 tty62
crw--w---- 1 root tty       4,  63 Feb  2 19:32 tty63
crw--w---- 1 root tty       4,   7 Feb  2 19:32 tty7
crw--w---- 1 root tty       4,   8 Feb  2 19:32 tty8
crw--w---- 1 root tty       4,   9 Feb  2 19:32 tty9
crw-rw---- 1 root dialout 204,  64 Feb  2 19:32 ttyAMA0
crw------- 1 root root      5,   3 Feb  2 19:32 ttyprintk
crw------- 1 root root     10, 239 Feb  2 19:32 uhid
crw------- 1 root root     10, 223 Feb  2 19:32 uinput
crw-rw-rw- 1 root root      1,   9 Feb  2 19:32 urandom
crw------- 1 root root    250,   0 Feb  2 19:32 vc-cma
crw-rw---- 1 root video   246,   0 Feb  2 19:32 vchiq
crw-rw---- 1 root video   248,   0 Feb  2 19:32 vcio
crw------- 1 root root    249,   0 Feb  2 19:32 vc-mem
crw-rw---- 1 root tty       7,   0 Feb  2 19:32 vcs
crw-rw---- 1 root tty       7,   1 Feb  2 19:32 vcs1
crw-rw---- 1 root tty       7,   2 Feb  2 19:32 vcs2
crw-rw---- 1 root tty       7,   3 Feb  2 19:32 vcs3
crw-rw---- 1 root tty       7,   4 Feb  2 19:32 vcs4
crw-rw---- 1 root tty       7,   5 Feb  2 19:32 vcs5
crw-rw---- 1 root tty       7,   6 Feb  2 19:32 vcs6
crw-rw---- 1 root tty       7, 128 Feb  2 19:32 vcsa
crw-rw---- 1 root tty       7, 129 Feb  2 19:32 vcsa1
crw-rw---- 1 root tty       7, 130 Feb  2 19:32 vcsa2
crw-rw---- 1 root tty       7, 131 Feb  2 19:32 vcsa3
crw-rw---- 1 root tty       7, 132 Feb  2 19:32 vcsa4
crw-rw---- 1 root tty       7, 133 Feb  2 19:32 vcsa5
crw-rw---- 1 root tty       7, 134 Feb  2 19:32 vcsa6
crw-rw---- 1 root video   245,   0 Feb  2 19:32 vcsm
crw------- 1 root root     10, 137 Feb  2 19:32 vhci
crw------- 1 root root     10, 130 Feb  2 19:32 watchdog
crw------- 1 root root    252,   0 Feb  2 19:32 watchdog0
prw-r----- 1 root adm            0 Feb  2 19:39 xconsole
crw-rw-rw- 1 root root      1,   5 Feb  2 19:32 zero
brock@uncacsci-pi3-d:/sys/bus$ ls -l /sys/class/gpio/
total 0
-rwxrwx--- 1 root gpio 4096 Feb  2 20:19 export
lrwxrwxrwx 1 root gpio    0 Feb  2 20:19 gpio27 -> ../../devices/platform/soc/3f200000.gpio/gpiochip0/gpio/gpio27
lrwxrwxrwx 1 root gpio    0 Feb  2 19:32 gpiochip0 -> ../../devices/platform/soc/3f200000.gpio/gpio/gpiochip0
lrwxrwxrwx 1 root gpio    0 Feb  2 19:32 gpiochip100 -> ../../devices/gpiochip2/gpio/gpiochip100
lrwxrwxrwx 1 root gpio    0 Feb  2 19:32 gpiochip128 -> ../../devices/gpiochip1/gpio/gpiochip128
-rwxrwx--- 1 root gpio 4096 Feb  2 20:19 unexport
brock@uncacsci-pi3-d:/sys/bus$ ls -l /sys/bus/gpio/
total 0
drwxr-xr-x 2 root root    0 Dec 31  1969 devices
drwxr-xr-x 2 root root    0 Dec 31  1969 drivers
-rw-r--r-- 1 root root 4096 Feb  2 20:59 drivers_autoprobe
--w------- 1 root root 4096 Feb  2 20:59 drivers_probe
--w------- 1 root root 4096 Dec 31  1969 uevent
brock@uncacsci-pi3-d:/sys/bus$ ls -l /sys/bus/gpio/devices/
total 0
lrwxrwxrwx 1 root root 0 Dec 31  1969 gpiochip0 -> ../../../devices/platform/soc/3f200000.gpio/gpiochip0
lrwxrwxrwx 1 root root 0 Dec 31  1969 gpiochip1 -> ../../../devices/gpiochip1
lrwxrwxrwx 1 root root 0 Dec 31  1969 gpiochip2 -> ../../../devices/gpiochip2
brock@uncacsci-pi3-d:/sys/bus$ ls -l /sys/bus/gpio/drivers
total 0
brock@uncacsci-pi3-d:/sys/bus$ ls /dev/gpio*
/dev/gpiochip0  /dev/gpiochip1  /dev/gpiochip2  /dev/gpiomem
brock@uncacsci-pi3-d:/sys/bus$ ls -l /dev/gpio*
crw------- 1 root root 254, 0 Feb  2 19:32 /dev/gpiochip0
crw------- 1 root root 254, 1 Feb  2 19:32 /dev/gpiochip1
crw------- 1 root root 254, 2 Feb  2 19:32 /dev/gpiochip2
crw-rw---- 1 root gpio 243, 0 Feb  2 19:32 /dev/gpiomem
brock@uncacsci-pi3-d:/sys/bus$ echo https://www.kernel.org/doc/Documentation/gpio/drivers-on-gpio.txt
https://www.kernel.org/doc/Documentation/gpio/drivers-on-gpio.txt
brock@uncacsci-pi3-d:/sys/bus$ echo https://www.kernel.org/doc/Documentation/gpio/
https://www.kernel.org/doc/Documentation/gpio/
brock@uncacsci-pi3-d:/sys/bus$ echo https://www.raspberrypi.org/forums/viewtopic.php?f=29&t=130811
[1] 1378
brock@uncacsci-pi3-d:/sys/bus$ https://www.raspberrypi.org/forums/viewtopic.php?f=29

https://github.com/torvalds/linux/tree/master/Documentation/gpio
https://github.com/torvalds/linux/tree/master/tools/gpio

https://raspberrypi.stackexchange.com/questions/40105/access-gpio-pins-without-root-no-access-to-dev-mem-try-running-as-root

/dev/mem vs /dev/gpiomem

http://bob.cs.sonoma.edu/IntroCompOrg-RPi/intro-co-rpi.html
http://bob.cs.sonoma.edu/IntroCompOrg-x64/book.html

https://www.cnx-software.com/2017/11/03/learn-more-about-linuxs-new-gpio-user-space-subsystem-libgpiod/
