netdev - Re: [PATCH v4 0/3] IR decoding using BPF

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Date:   Wed, 23 May 2018 14:21:27 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Sean Young <sean@...s.org>, linux-media@...r.kernel.org,
        linux-kernel@...r.kernel.org, Alexei Starovoitov <ast@...nel.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        netdev@...r.kernel.org, Matthias Reichl <hias@...us.com>,
        Devin Heitmueller <dheitmueller@...nellabs.com>,
        Y Song <ys114321@...il.com>,
        Quentin Monnet <quentin.monnet@...ronome.com>
Subject: Re: [PATCH v4 0/3] IR decoding using BPF

On 05/18/2018 04:07 PM, Sean Young wrote:
> 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.

Mauro, are you fine with this series going via bpf-next? How ugly would this
get with regards to merge conflicts wrt drivers/media/rc/?

Thanks,
Daniel

> 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 <ys114321@...il.com> and
>    Randy Dunlap <rdunlap@...radead.org>
>  - 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
>