Pad configuration in imx8mp firmware

[YorkerHazan]

Hello,

I have a custom carrier board that is connected to the imx8mp soc.

In my board I use `gpio4_27` (which is ALT 5 of the `SAI2_MCLK` pin).

Upon booting it seems that said gpio pulls high, which is a strange behavior since I hadn't defined anywhere in the dts/user space to toggle said gpio. This causes some unwanted behavior for me.

To further reduce down the problem I immediately terminated after startup in u-boot but the pin still pulls high even though the u-boot is terminated and does not reach any dts parsing/hardware configuration.

I feel like I have no choice but to suspect the firmware, since the issue seems to occur prior to u-boot.

Since we're discussing imx8mp which doesn't contain the scfw for pin configuration, where should I look further to find the issue?

Is there any chance that the issue lies in nxp's firmware which isn't open sourced (AKA isn't a part of the ATF)?

Could this occur due to the fact that the default pin configuration of this pin isn't gpio? could the firmware be pulling it high by default?

This is very confusing, and I am not sure I have the correct terminology or understanding of the imx firmware, any help would be greatly appreciated!

[Manuel_Salas]

Hello @YorkerHazan 

I hope you are doing very well.

Could you please confirm that you have not configured the SAI2_MCLK PAD on U-boot device Tree or Linux Device tree?

If you are using the U-Boot device tree from the EVK, you can see that pin is used for the FlexCAN module and configures the PAD with Pull-Up enable:

Also, the same configuration on Linux device tree:

Could you please check it, or define your PAD with your desired configuration to avoid this kind of behaviors.

Best regards,

Salas.

[YorkerHazan]

Hello @Manuel_Salas , your response is greatly appreciated!

I am not using the device tree from the EVK.
Actually, I edited u-boot's source code to hang immediately on boot - meaning no dts parsing occurs.
This is why my suspicion of the firmware began in the first place.

Anyhow I doubled checked the dts ( even though the code that handles never runs ) and this pin isn't configured anywhere.

Is it possible that the firmware configures this pin/pulls it high for some reason?
I know that such thing is possible in imx8qm in the scfw, is such thing also possible in imx8mp?

Thank you!