NFC

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Near-field communication (NFC) can be used for contactless exchange of data over short distances. Different approaches exist on Linux to support it:

  • libnfc: userspace implementation, but mostly for desktop (e.g. USB) readers
  • Android NFC HAL: doesn't really work outside Android, probably mostly proprietary implementations
  • Linux NFC subsystem: NFC abstraction in the (mainline) Linux kernel with support for many different (also embedded) NFC chips

For smartphones/embedded devices the Linux NFC subsystem is the most suitable one, because it can just be set up normally in the device tree like other hardware. Unfortunately, the NFC subsystem has been somewhat unmaintained for quite some time, and especially the userspace portion of it: Neard.

However, the main problem when testing NFC is a lack of applications that can make use of the Linux NFC subsystem. If you know any useful applications, please add them here. Also note that there is support for NFC/Neard in Qt if you want to build an application that makes use of NFC yourself.

Devices with NFC support

If your device runs the mainline kernel, and has a NFC chip that is supported in mainline's Linux NFC subsystem it should be fairly easy to add it to the device tree. Check the available NFC device tree bindings for details. Otherwise, these devices in postmarketOS already support NFC to some extent:

Device Codename Category
Samsung Galaxy A3 (2015) samsung-a3ulte, samsung-a3lte community
Samsung Galaxy A5 (2015) samsung-a5ulte, samsung-a5lte community
Samsung Galaxy S4 Mini Value Edition samsung-serranovelte community
Xiaomi Mi Note 2 xiaomi-scorpio community
Google (ASUS) Nexus 7 (2012) asus-grouper testing
Huawei Ascend G7 huawei-g7 testing
Xiaomi Mi 5 xiaomi-gemini testing

Testing

At the moment there are not many useful applications for testing NFC. As a basic test, you can use nfctool (from apk add neard) to poll for devices:

$ nfctool -d nfc0 -1 -p
nfc0:
          Tags: [ ]
          Devices: [ ]
          Protocols: [ Felica MIFARE Jewel ISO-DEP ISO-15693 ]
          Powered: Yes
          RF Mode: None
          lto: 0
          rw: 0
          miux: 0

Start polling on nfc0 as initiator

Targets found for nfc0
  Tags: [ tag0 ]
  Devices: [ ]

If you hold some other NFC-capable device close to the NFC antenna, it should find a NFC tag and show it. Many chip cards nowadays have NFC, or maybe you can use another smartphone.

Note Note: You may need to search for a while to find a working spot on the phone close to the NFC antenna. It could be anywhere on the back or anywhere on the front so just search for a bit before you give up.

Reading NFC tags

For advanced usage you should start the Neard daemon (rc-service neard start). Neard then provides a DBUS API similar to BlueZ for Bluetooth that allows reading/writing NFC tags for example.

The easiest way to test it is using the Neard test scripts. Unfortunately Neard hasn't been updated for a long time so they still use Python 2. I had some success making test-adapter and test-tag work on Python 3 using 2to3 but overall it's incomplete and only partially working.

Upstream is looking for potential maintainers and testers of the Linux NFC subsystem, so if you would like to help, consider posting on the linux-nfc mailing list.

See also