After installing Kodi on a Raspberry Pi 4, I found that my Streamzap remote control worked for everything except the Ok and Exit buttons (which are supposed to get mapped to Enter and Back respectively).

A very old set of instructions for this is archived on the Kodi wiki but here's a more modern version of it.

Root cause

I finally tracked down the problem by enabling debug logging in Kodi settings. I saw the following in ~/.kodi/temp/kodi.log when presing the OK button:

DEBUG: Keyboard: scancode: 0x00, sym: 0x0000, unicode: 0x0000, modifier: 0x0
DEBUG: GetActionCode: Trying Hardy keycode for 0xf200
DEBUG: Previous line repeats 3 times.
DEBUG: HandleKey: long-0 (0x100f200, obc-16838913) pressed, action is
DEBUG: Keyboard: scancode: 0x00, sym: 0x0000, unicode: 0x0000, modifier: 0x0

and this when pressing the Down button:

DEBUG: CLibInputKeyboard::ProcessKey - using delay: 500ms repeat: 125ms
DEBUG: Thread Timer start, auto delete: false
DEBUG: Keyboard: scancode: 0x6c, sym: 0x0112, unicode: 0x0000, modifier: 0x0
DEBUG: HandleKey: down (0xf081) pressed, action is Down
DEBUG: Thread Timer 2502349008 terminating
DEBUG: Keyboard: scancode: 0x6c, sym: 0x0112, unicode: 0x0000, modifier: 0x0

This suggests that my Streamzap remote is recognized as a keyboard, which I can confirm using:

$ cat /proc/bus/input/devices 
I: Bus=0003 Vendor=0e9c Product=0000 Version=0100
N: Name="Streamzap PC Remote Infrared Receiver (0e9c:0000)"
P: Phys=usb-0000:01:00.0-1.2/input0
S: Sysfs=/devices/platform/scb/fd500000.pcie/pci0000:00/0000:00:00.0/0000:01:00.0/usb1/1-1/1-1.2/1-1.2:1.0/rc/rc0/input4
U: Uniq=
H: Handlers=kbd event0 
B: PROP=20
B: EV=100017
B: KEY=3ff 0 0 0 fc000 1 0 0 0 0 18000 4180 c0000801 9e1680 0 0 0
B: REL=3
B: MSC=10

Installing LIRC

The fix I found is to put the following in /etc/X11/xorg.conf.d/90-streamzap-disable.conf:

Section "InputClass"
    Identifier "Ignore Streamzap IR"
    MatchProduct "Streamzap"
    MatchIsKeyboard "true"
    Option "Ignore" "true"
EndSection

to prevent the remote from being used as a keyboard and to instead use it via LIRC, which can be installed like this:

apt install lirc lirc-compat-modules

Put the following in /etc/lirc/lirc_options:

driver=default
device=/dev/lirc0

and add the remote config for the Streamzap:

cd /etc/lirc/lircd.conf.d/
ln -s /usr/share/lirc/remotes/streamzap/lircd.conf.streamzap streamzap.conf

Testing

Now you should be able to test the remote using:

mode2

to see the undecoded infra-red signal, and:

irw

to display the decoded key presses.

Kodi configuration

Finally, as the pi user, put the following config in ~/.kodi/userdata/Lircmap.xml:

<lircmap>
  <remote device="Streamzap_PC_Remote">
    <power>KEY_POWER</power>
    <play>KEY_PLAY</play>
    <pause>KEY_PAUSE</pause>
    <stop>KEY_STOP</stop>
    <forward>KEY_FORWARD</forward>
    <reverse>KEY_REWIND</reverse>
    <left>KEY_LEFT</left>
    <right>KEY_RIGHT</right>
    <up>KEY_UP</up>
    <down>KEY_DOWN</down>
    <pageplus>KEY_CHANNELUP</pageplus>
    <pageminus>KEY_CHANNELDOWN</pageminus>
    <select>KEY_OK</select>
    <back>KEY_EXIT</back>
    <menu>KEY_MENU</menu>
    <red>KEY_RED</red>
    <green>KEY_GREEN</green>
    <yellow>KEY_YELLOW</yellow>
    <blue>KEY_BLUE</blue>
    <skipplus>KEY_NEXT</skipplus>
    <skipminus>KEY_PREVIOUS</skipminus>
    <record>KEY_RECORD</record>
    <volumeplus>KEY_VOLUMEUP</volumeplus>
    <volumeminus>KEY_VOLUMEDOWN</volumeminus>
    <mute>KEY_MUTE</mute>
    <record>KEY_RECORD</record>
    <one>KEY_1</one>
    <two>KEY_2</two>
    <three>KEY_3</three>
    <four>KEY_4</four>
    <five>KEY_5</five>
    <six>KEY_6</six>
    <seven>KEY_7</seven>
    <eight>KEY_8</eight>
    <nine>KEY_9</nine>
    <zero>KEY_0</zero>
  </remote>
</lircmap>

In order for all of this to take effect, I simply rebooted the Pi:

sudo systemctl reboot