Subject: [PATCH v4 0/3] IR decoding using BPF

From: Sean Young <[email-masked]>
Date: Fri, 18 May 2018 15:07:27 +0100

The kernel IR decoders (drivers/media/rc/ir-*-decoder.c) support the most
widely used IR protocols, but there are many protocols which are not
supported[1]. For example, the lirc-remotes[2] repo has over 2700 remotes,
many of which are not supported by rc-core. There is a "long tail" of
unsupported IR protocols, for which lircd is need to decode the IR .

IR encoding is done in such a way that some simple circuit can decode it;
therefore, bpf is ideal.

In order to support all these protocols, here we have bpf based IR decoding.
The idea is that user-space can define a decoder in bpf, attach it to
the rc device through the lirc chardev.

Separate work is underway to extend ir-keytable to have an extensive library
of bpf-based decoders, and a much expanded library of rc keymaps.

Another future application would be to compile IRP[3] to a IR BPF program, and
so support virtually every remote without having to write a decoder for each.
It might also be possible to support non-button devices such as analog
directional pads or air conditioning remote controls and decode the target
temperature in bpf, and pass that to an input device.

Thanks,

Sean Young

[1] http://www.hifi-remote.com/wiki/index.php?title=DecodeIR
[2] https://sourceforge.net/p/lirc-remotes/code/ci/master/tree/remotes/
[3] http://www.hifi-remote.com/wiki/index.php?title=IRP_Notation

Changes since v3:
 - Implemented review comments from Quentin Monnet and Y Song (thanks!)
 - More helpful and better formatted bpf helper documentation
 - Changed back to bpf_prog_array rather than open-coded implementation
 - scancodes can be 64 bit
 - bpf gets passed values in microseconds, not nanoseconds.
   microseconds is more than than enough (IR receivers support carriers upto
   70kHz, at which point a single period is already 14 microseconds). Also,
   this makes it much more consistent with lirc mode2.
 - Since it looks much more like lirc mode2, rename the program type to
   BPF_PROG_TYPE_LIRC_MODE2.
 - Rebased on bpf-next

Changes since v2:
 - Fixed locking issues
 - Improved self-test to cover more cases
 - Rebased on bpf-next again

Changes since v1:
 - Code review comments from Y Song <[email-masked]> and
   Randy Dunlap <[email-masked]>
 - Re-wrote sample bpf to be selftest
 - Renamed RAWIR_DECODER -> RAWIR_EVENT (Kconfig, context, bpf prog type)
 - Rebase on bpf-next
 - Introduced bpf_rawir_event context structure with simpler access checking

Sean Young (3):
  bpf: bpf_prog_array_copy() should return -ENOENT if exclude_prog not
    found
  media: rc: introduce BPF_PROG_LIRC_MODE2
  bpf: add selftest for lirc_mode2 type program

 drivers/media/rc/Kconfig                      |  13 +
 drivers/media/rc/Makefile                     |   1 +
 drivers/media/rc/bpf-lirc.c                   | 308 ++++++++++++++++++
 drivers/media/rc/lirc_dev.c                   |  30 ++
 drivers/media/rc/rc-core-priv.h               |  22 ++
 drivers/media/rc/rc-ir-raw.c                  |  12 +-
 include/linux/bpf_rcdev.h                     |  30 ++
 include/linux/bpf_types.h                     |   3 +
 include/uapi/linux/bpf.h                      |  53 ++-
 kernel/bpf/core.c                             |  11 +-
 kernel/bpf/syscall.c                          |   7 +
 kernel/trace/bpf_trace.c                      |   2 +
 tools/bpf/bpftool/prog.c                      |   1 +
 tools/include/uapi/linux/bpf.h                |  53 ++-
 tools/include/uapi/linux/lirc.h               | 217 ++++++++++++
 tools/lib/bpf/libbpf.c                        |   1 +
 tools/testing/selftests/bpf/Makefile          |   8 +-
 tools/testing/selftests/bpf/bpf_helpers.h     |   6 +
 .../testing/selftests/bpf/test_lirc_mode2.sh  |  28 ++
 .../selftests/bpf/test_lirc_mode2_kern.c      |  23 ++
 .../selftests/bpf/test_lirc_mode2_user.c      | 154 +++++++++
 21 files changed, 974 insertions(+), 9 deletions(-)
 create mode 100644 drivers/media/rc/bpf-lirc.c
 create mode 100644 include/linux/bpf_rcdev.h
 create mode 100644 tools/include/uapi/linux/lirc.h
 create mode 100755 tools/testing/selftests/bpf/test_lirc_mode2.sh
 create mode 100644 tools/testing/selftests/bpf/test_lirc_mode2_kern.c
 create mode 100644 tools/testing/selftests/bpf/test_lirc_mode2_user.c

-- 
2.17.0