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.