quoted

and now in s5pc200 code, you can also register/re-use the s5pc100_keypad
device/driver, and everyone knows - OK, the IP on S5PC100 is now re-used
here.

This is naming issue and i know it was not desided yet.
This keypad driver can support s3c64xx, s5pc100, s5pc110, s5pv210.

I bet the first silicon this IP is deployed is s3c64xx, so my understanding
's3c64xx-keypad.c' should be an acceptable name.  And it's also reasonable,
a s3c64xx-keypad driver, and is later expanded to support subsequent silicons
without the file name being changed.