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Some IIO drivers feature an optional debug facility, allowing users to read or write registers directly. Special care needs to be taken when using this feature, since you can modify registers on the back of the driver.

Tip

To simplify direct register access you may want to use the libiio Libiio command line utility.

Accessing debugfs requires root privileges.

In order to identify if the IIO device in question feature this option you first need to identify the IIO device number.

Therefore read the name attribute of each IIO device

~$

grep "" /sys/bus/iio/devices/iio\:device*/name

/sys/bus/iio/devices/iio:device0/name:ad7291
/sys/bus/iio/devices/iio:device1/name:ad9361-phy
/sys/bus/iio/devices/iio:device2/name:xadc
/sys/bus/iio/devices/iio:device3/name:adf4351-udc-rx-pmod
/sys/bus/iio/devices/iio:device4/name:adf4351-udc-tx-pmod
/sys/bus/iio/devices/iio:device5/name:cf-ad9361-dds-core-lpc
/sys/bus/iio/devices/iio:device6/name:cf-ad9361-lpc

Change directory to /sys/kernel/debug/iio/ iio:deviceX and check if the direct_reg_access file exists.

~$

cd /sys/kernel/debug/iio/iio\:device1

/sys/kernel/debug/iio/iio:device1$

ls direct_reg_access

direct_reg_access

Reading

/sys/kernel/debug/iio/iio:device1$

echo 0x7 > direct_reg_access

/sys/kernel/debug/iio/iio:device1$

cat direct_reg_access

0x40

Writing

/sys/kernel/debug/iio/iio:device1$

echo 0x7 0x50  > direct_reg_access

/sys/kernel/debug/iio/iio:device1$

cat direct_reg_access

0x50

Accessing HDL CORE registers

Special ADI device driver convention for devices that have both:

a SPI/I2C control interface
and some sort of HDL Core with registers (AXI)

In this case when accessing the HDL Core Registers always set BIT31.

The register map for ADI HDL cores can be found at section “Register Map” of each IP Cores documentation (example).

/sys/kernel/debug/iio/iio:device6$

echo 0x80000000 > direct_reg_access

/sys/kernel/debug/iio/iio:device6$

cat direct_reg_access

0x80062