Retain GPIO5_IO13 value when switching from U-Boot to Linux Kernel

[nissim_alcon]

Dear All,

I am using the Variscite's VAR-SOM-SOLO/DUAL which is based on the I.MX6 Solo processor. In addition, Yocto (Thud kernel 4.14.78) is being used as the OS.

I wish to use GPIO5_IO13 as General purpose output pin from the moment the U-Boot starts. For that matter several changes were made as follows:

1. U-Boot: configure the GPIO5 IO13 to be output with 100K pullup resistor

2. Kernel device tree: in imx6qdl-var-som.dtsi add the following line to iomux pinctrl_hog group:  MX6QDL_PAD_DISP0_DAT19__GPIO5_IO13  0x80000000

As far as i know, 0x80000000 instruct the iomux kernel driver to ignore the configuration of the bin and by that leave the configuration with the values that were configured in the U-boot.

By using a scope i can see that the GPIO drops to low and goes back to high when kernel starts.

Please advise,

Nissim

Nissim

[igorpadykov]

Hi Nissim

in general your understanding is correct, 0x80000000 means pad configuration should be

derived from uboot. One can try to debug this behaviour, which may be specific for that board,

probably this signal is used by other board peripheral, use AN4553 Using Open

Source Debugging Tools for Linux on i.MX Processors:

https://www.nxp.com/docs/en/application-note/AN4553.pdf

Best regards
igor

[nissim_alcon]

Dear Igor,

Thanks for the information.

Nissim