I encountered the following behavior (an issue for me) while working with 
PRUs, device trees overlays and the gpio export filesystem.

I guess this is a kernel related problem to the filesystem drivers in 
/sys/class/gpio/export, I have a stable-4.4-bone-rt kernel on a debian. 

when I define a custom boot configuration, for example two gpios of the 
peripheral gpio2 they get correctly configured as outputs and the PRU 
normally manages them (or other process that access to the gpio2 peripheral 
through memory mapping) until I export another GPIO from the same 
peripheral (gpio2) but another gpio. It's like if they are all reset to 
inputs during the export ignoring the initial device tree configuration.
I discovered thsi while using BeagleG + Adafruit python library (that uses 
internally the filesystem exports) and what I found was that the dto 
configuration gets overridden during the export.
What I did to solve the problem was a simple script that exported for each 
peripheral the first gpio solving the issue.

Is this meant to be like that? Shouldn't the kernel respect the dto 

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