Open-collector GPIO usage question

[Matthias Urlichs <matthias@urlichs.de>]

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Hi,

so I want to efficiently implement a bit-bang-ish protocol, meaning I'd 
like to use events instead of busy-looping.

The hardware uses open-collector wiring.

This doesn't seem possible with Linux GPIO.

I cannot set input and output flags at the same time. Getting events 
requires the input flag while the open-drain output flag requires, well, 
output. Owch.

AFAICS all of this is enforced by 
drivers/gpio/gpiolib-cdev.c::gpio_v2_line_flags_validate(), so not gpio 
driver specific.

As some hardware seems capable enough to trigger an interrupt on raw 
port levels even if configured for "output", this seems overly 
restrictive … also, I happen to not have enough GPIO ports to use two 
per wire.

Thoughts?

-- 
-- regards
-- 
-- Matthias Urlichs


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