Earliest possible GPIO toggle on i.mx6

[Mayur Nande]

Hello all,

I have a question regarding the earliest possible GPIO toggle with barebox on imx6. We use boards with imx6 quad core processor (from Phytec). In our hardware design we have a push button controller which has a "KILL" pin attached to one of the GPIO pins on i.mx6. The requirement is that this pin should be set to 1 within 400 ms of power on. I tried setting this at various places in barebox with incremental improvements starting from the init script, board.c, lowlevel.c and then DCD/lowlevel.c combination. 

The best performance I got was by setting the iomux registers (IOMUXC_SW_MUX_CTL_PAD and IOMUXC_SW_PAD_CTL_PAD) in DCD and the GPIO direction and value registers in lowlevel.c (since GPIO controller registers are not accessible with DCD). Even with this, I get the GPIO set in around 460-475ms at the best. I understand that some of the time here is used by the hardware for voltage regulation/crystal stabilization which probably we can't do anything about.

>From barebox side, any suggestions or ideas to improve this would be very helpful.
Thank you very much.        

Warm Regards,
Mayur Nande