kbscan: Increase debounce time from 10ms to 20ms

[uSpike]

I found that a debounce time of 10ms was causing very frequent twice-registered keys with my typing style. After setting the debounce time to 20ms I find that no repeated characters occur when typing 10 line of text.

Fixes: https://github.com/system76/firmware-open/issues/509

[uSpike]

Any chance this could be merged? I've not upgraded EC for some time waiting for this..

[jacobgkau]

Just want to point out that this value was originally set to 20ms. It was reduced to 15ms alongside other behavior improvements: https://github.com/system76/ec/pull/60

After that, anther user wanted it moved all the way down to 3ms: https://github.com/system76/ec/pull/359

As a compromise, we went to 5ms (https://github.com/system76/ec/pull/378), but later raised it back up to the current 10ms (https://github.com/system76/ec/pull/405).

I wonder if this config needs to be more board-specific (if the ghosting behavior differs per laptop), or if it should just be more user-configurable without having to build custom firmware, since there's been so much push and pull on different values. It's possible the behavior improvements in https://github.com/system76/ec/pull/60 would've made it work alright without changing the value at that time, but it's also possible another user comes along wanting another timing change after this is merged.