i.MX ProcessorsのトピックRe: Retain GPIO5_IO13 value when switching from U-Boot to Linux Kernel

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

nissim_alcon — Mon, 12 Oct 2020 12:55:20 GMT

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

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

igorpadykov — Tue, 13 Oct 2020 00:09:02 GMT

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

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

nissim_alcon — Sun, 29 Nov 2020 14:23:13 GMT

Dear Igor,

Thanks for the information.

Nissim