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It seems like you are trying to configure a GPIO pin (SODIMM_135) on your iMX6ULL module with a Viola carrier board to handle the power-off sequence. You have set up the device tree entry for the gpio-poweroff driver, but you are observing a square wave of 215ms instead of the expected behavior.
Here are a few things to check and consider:
Device Tree Configuration:
Ensure that the device tree configuration is correct. Your configuration looks correct, but double-check the pin number and GPIO bank. For SODIMM_135 on the iMX6ULL, it should be:
Pin Muxing:
Verify that the pin is correctly muxed as a GPIO in the device tree. If the pin is not muxed correctly, it might not function as expected. You can add the pin muxing configuration in the device tree:
Kernel Configuration:
Ensure that the CONFIG_POWER_RESET_GPIO option is enabled in your kernel configuration. This option is necessary for the gpio-poweroff driver to work:
CONFIG_POWER_RESET_GPIO=y
Behavior of the GPIO:
The square wave of 215ms you are observing might be due to the GPIO toggling state during the shutdown process. This could be caused by the GPIO being reconfigured or driven by another part of the system. Ensure that no other part of the system is driving this GPIO during shutdown.
Debugging:
You can add some debug prints in the kernel driver to see if the gpio-poweroff driver is being called correctly and if the GPIO is being set as expected. This can help you understand if the issue is with the driver or the hardware configuration.
If you have checked all the above points and the issue persists, it might be helpful to provide more details about the exact behavior you are observing and any additional logs or messages from the kernel during the shutdown process.
Please, also check if these links can help you solve your problem: