Is it possible to configure any of the pins that are marked as reserved in the Verdin Family Specifications as GPIOs? Specifically we have an adapter card that currently connects SODIMM_219 and SODIMM_16 to our system in such a way that they need to be configured as GPIO outputs.
I have been able to make them available by modifying the device tree and I have confirmed that linux identifies the pin as an output, but when probing the pin I see no change in state when I run my test script which cycles between high and low.
According to the “Verding Specification” “Reserved” interfaces are features that are defined and reserved but possibly missing on some SoMs. The reason for that could be that certain SoCs do not feature an interface, or there is an assembly option that omits certain interfaces for cost optimization. Replacement pins must be electrically compatible with the specified functionality. This means that any Verdin SoM can be inserted into any Verdin carrier board without risking damage caused by incompatible reserved pins.
Since the “Reserved” interfaces are possibly missing on some SoC, it is mandatory to consult the module datasheet for further information.
In summary, you can use Alt functions (such as GPIO) on reserved pins, but it will break compatibility of your carrier board with other kinds of Verdin modules.
According to the Verdin iMX8M Plus datasheet, the SODIMM_219 can be configured as GPIO4_IO13, and the SODIMM_16 as GPIO1_IO11. To use these pins for the desired purpose, you need to modify the pin muxing for selected pins at the Device Tree.
The mentioned thread related to the Colibri iMX7 pin reserved for ResetOut# is a completely different case and has nothing in common with your request.
Ok thank you for confirming that the GPIO ALT should be possible.
Do you know of any testing that has been done to confirm this configuration? I see there have been software releases of toradex image that have had bugs that prevent control of certain GPIOs but not others (see discussion here: Some GPIO pins work as expectation, but some pins don't - #8 by tanchunhau).
We have attempted explicitly configuring the Pin control register per the muxing instructions. The GPIO remains accessible in gpioinfo as before, and is even shown as an output when our code is activating it, yet we still have no voltage change when connecting a logic level shifter (TXB0108) to LED+2k Resistor (low current LED). This same hardware test has been used to confirm the majority of our other GPIOs, these are the only 2 GPIOs that do not work.
Have you checked in the device tree if these pins are already being referenced/used by any other devices? If that’s the case the GPIO functionality would not work.
