GPIO permission errors after upgrade to 3.18.x (Raspbian)

When the latest package raspberrypi-bootloader:armhf 1.20150130-1 was installed, the gpio symbolic links in /sys/class/gpio/ moved from /sys/devices/virtual/ to /sys/devices/soc/20200000.gpio.

The permissions in /sys/devices/soc/20200000.gpio do not include the "x" bit, as as such nobody but root can use the gpio.

This has changed since the latest bootloader, and the only way I can fix this is on boot, as root, run

chmod -R +x /sys/devices/soc/20200000.gpio

Is there a better way to allow a non-root user to access the GPIO?

[fivdi]

I think this is happening because /lib/udev/rules.d/60-python-pifacecommon.rules and /lib/udev/rules.d/60-python3-pifacecommon.rules no longer function as expected.

For example, here's /lib/udev/rules.d/60-python3-pifacecommon.rules:

KERNEL=="spidev*", GROUP="spi", MODE="0660"
SUBSYSTEM=="gpio*", PROGRAM="/bin/sh -c 'chown -R root:gpio /sys/class/gpio && chmod -R 770 /sys/class/gpio; chown -R root:gpio /sys/devices/virtual/gpio && chmod -R 770 /sys/devices/virtual/gpio'"

The directory /sys/devices/virtual/gpio no longer exists, so the rule doesn't work.

[popcornmix]

Does disabling device-tree (add "device_tree=" to config.txt) work around the issue?

Ping @pelwell @asb

[OliverHoermann]

I came round this issue when testing my PiFace Digital, where pifacecommon/interrupts.py threw an exception of not finding /sys/devices/virtual/gpio.
Setting device_tree=off in config.txt makes /sys/devices/virtual/gpio reappear.
After that, PiFace Digital works as expected again.

BR
Oliver

[pelwell]

Can somebody explain how PiFace (my phone really wanted to write "pigface" there) uses these file nodes, and why it doesn't/can't use the nodes under /sys/class/gpio/ instead?

[popcornmix]

I believe it's just used in /lib/udev/rules.d/60-python3-pifacecommon.rules (which we include in raspbian image)

[pelwell]

I don't buy that. Why bother changing permissions on files or directories that you aren't otherwise going to use?

[OliverHoermann]

Phil,
the /sys/..../gpio is used in pifacecommons/interrupts.py.

I tried changing above file. Pifacedigital-emulator started up afterwards,
but didn't read the input lines then. Only output settings worked.

Hope that helped,
Oliver

Am 07.02.2015 um 20:10 schrieb Phil Elwell notifications@github.com:

I don't buy that. Why bother changing permissions on files or directories
that you aren't otherwise going to use?

—
Reply to this email directly or view it on GitHub
#791 (comment).

[fivdi]

In order for user pi to be able to access gpios without root permissions on a michine with the device tree disabled, udev rules are needed for both /sys/class/gpio and /sys/devices/virtual/gpio. They are needed for /sys/devices/virtual/gpio because the gpioN directories in /sys/class/gpio are links to the gpioN directories in /sys/devices/virtual/gpio. For example, see directory gpio4 here:

pi@raspberrypi /sys/class/gpio $ echo 4 > export 
pi@raspberrypi /sys/class/gpio $ ls -la
total 0
drwxrwx---  2 root gpio    0 Feb  7 20:11 .
drwxr-xr-x 38 root root    0 Feb  7 19:28 ..
-rwxrwx---  1 root gpio 4096 Feb  7 20:11 export
lrwxrwxrwx  1 root gpio    0 Feb  7 20:11 gpio4 -> ../../devices/virtual/gpio/gpio4
lrwxrwxrwx  1 root gpio    0 Jan  1  1970 gpiochip0 -> ../../devices/virtual/gpio/gpiochip0
-rwxrwx---  1 root gpio 4096 Feb  7 19:40 unexport
pi@raspberrypi /sys/class/gpio $ 

I can't think of a sane reason to use /sys/devices/virtual/gpio in source code as /sys/class/gpio can always be used instead, if I'm not mistaken.

Note that this only functions when the device tree is disabled. When the device tree is enabled, /sys/devices/virtual/gpio disappears.

If the device tree is enabled, the udev rules on the Pi 2 need to use /sys/devices/soc/3f200000.gpio/gpio/ instead. The address 3f200000 may be different on the Pi 1, I'm not sure.

Note that /sys/devices/virtual/gpio is used in both /lib/udev/rules.d/60-python3-pifacecommon.rules and /lib/udev/rules.d/60-python-pifacecommon.rules in Raspbian. I've no idea how many users rely on this now.

[pelwell]

Can somebody try this modified version of /lib/udev/rules.d/60-python-pifacecommon.rules (change either or both versions)?:

KERNEL=="spidev*", GROUP="spi", MODE="0660"
SUBSYSTEM=="gpio*", PROGRAM="/bin/sh -c 'chown -R root:gpio /sys/class/gpio && chmod -R 770 /sys/class/gpio; chown -R root:gpio /sys/devices/virtual/gpio && chmod -R 770 /sys/devices/virtual/gpio; chown -R root:gpio /sys/devices/soc/*.gpio/gpio && chmod -R 770 /sys/devices/soc/*.gpio/gpio'"

It should work with and without DT, on Pi1 and Pi2.

[tompreston]

Hi, I'm one of the Tom's at PiFace -- we're looking into this right now. :)

[tompreston]

@pelwell The new rule works when the interrupt module in pifacecommon points to /sys/class/gpio instead of /sys/devices/virtual/gpio. I'm going to patch this in and the updated package should go live asap.

[pelwell]

That sounds like the right change - you can think of /sys/class/gpio as the generic interface, and /sys/devices/*/gpio as the specific implementation.

[fivdi]

@pelwell The new rule you provided above also works for me. I'm not using PiFace, but rely on the rule to enable user pi on Raspbian to use gpio without root privileges. Thanks :)

[alexanderhaensch]

in /boot/config.txt

device_tree=

is the only solution for me. i am using lric_rpi and some gpios. even lirc_rpi dt_overlay is not working correctly... :(