Converting a data line to GPIO during run-time

[aabitria_]

Hello,

Is it practically feasible to turn a data line (e.g. certain UART TX and RX as well as SD2 CLK, CMD, and D0-D3 lines) to GPIO lines that can be tri-stated?  The goal is to put those pins to tristate/hi impedance which I think can be done by converting them to GPIO.  I do know that these data lines' configuration are set in the device tree like its MUX function, pullups, etc, and that configuration is carried out when the kernel is initialized.  Those data lines are being used for the entire session of the device and I'm told they have to be tristated just before turning off.  I'm using Android 7.1 in an iMX6DL processor.

Hoping for a response.  Thank you.

Alvin

[jimmychan]

Hello,

There is no pad setting to set the pin as tri-state.

For the details of PAD setting, please refer to the Reference Manual and search the "IOMUXC_SW_PAD_CTL_PAD".

[aabitria_]

Hello @jimmychan  

Thanks for the reply.  I think the part about tri-state is now known.  Just turn the GPIO into input, that's what I found from some NXP questions.

However, the question of how to turn a data line (e.g. certain UART TX and RX as well as SD2 CLK, CMD, and D0-D3 lines) initialized using device tree settings to GPIO lines still remains.  Is this possible in Linux or Android?

[jimmychan]

You may try this:

https://community.nxp.com/t5/i-MX-Processors/Runtime-pinmux-i-MX6SX/m-p/575614