Why setprop ro.nfc.port is needed in init.rc in android

Question

I am working on enabling NFC on the STE snowball board. I enabled the NFC and its working fine. While enabling I took help of internet and porting guide, where most of the links tell's following statement to write, In init.rc file, setprop ro.nfc.port "I2C" chmod 0600 /dev/pn544 and in ueventd.rc file, /dev/pn544 0600 system system I understand that defining the statement in ueventd.rc will create a node in /dev/ path, but I am not able to understand why setprop is written in init.rc file. Can any one give a pointer to understand the above issue ??

Answer 1

ro.nfc.port defines the transport used by the NFC subsystem to talk to the NFC chip. In your case the NFC chip is connected to the I²C bus with /dev/pn544 as the driver.

The libnfc also supports connecting the NFC chip to a serial port. This is done for example in the tuna platform (Galaxy Nexus I think). In this case you'll see:

setprop ro.nfc.port "COM4"
chmod 0600 /dev/ttyO3

in your init.rc

Unless you are building a platform by yourself you should not mess around with these settings. They are for system builders and they (hopefully) know what they're doing. Users won't see any benefit from modifying them.