diff options
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/media/uapi/rc/lirc-dev-intro.rst | 47 |
1 files changed, 38 insertions, 9 deletions
diff --git a/Documentation/media/uapi/rc/lirc-dev-intro.rst b/Documentation/media/uapi/rc/lirc-dev-intro.rst index 1a901d8e1797..a8733c8df2e7 100644 --- a/Documentation/media/uapi/rc/lirc-dev-intro.rst +++ b/Documentation/media/uapi/rc/lirc-dev-intro.rst @@ -20,6 +20,9 @@ data between userspace and kernelspace. Fundamentally, it is just a chardev file_operations defined on it. With respect to transporting raw IR and decoded scancodes to and fro, the essential fops are read, write and ioctl. +It is also possible to attach a BPF program to a LIRC device for decoding +raw IR into scancodes. + Example dmesg output upon a driver registering w/LIRC: .. code-block:: none @@ -34,6 +37,16 @@ What you should see for a chardev: $ ls -l /dev/lirc* crw-rw---- 1 root root 248, 0 Jul 2 22:20 /dev/lirc0 +Note that the package `v4l-utils <https://git.linuxtv.org/v4l-utils.git/>`_ +contains tools for working with LIRC devices: + + - ir-ctl: can receive raw IR and transmit IR, as well as query LIRC + device features. + + - ir-keytable: can load keymaps; allows you to set IR kernel protocols; load + BPF IR decoders and test IR decoding. Some BPF IR decoders are also + provided. + .. _lirc_modes: ********** @@ -129,12 +142,28 @@ on the following table. This mode is used only for IR send. - -************************** -Remote Controller protocol -************************** - -An enum :c:type:`rc_proto` in the :ref:`lirc_header` lists all the -supported IR protocols: - -.. kernel-doc:: include/uapi/linux/lirc.h +******************** +BPF based IR decoder +******************** + +The kernel has support for decoding the most common IR protocols, but there +are many protocols which are not supported. To support these, it is possible +to load an BPF program which does the decoding. This can only be done on +LIRC devices which support reading raw IR. + +First, using the `bpf(2)`_ syscall with the ``BPF_LOAD_PROG`` argument, +program must be loaded of type ``BPF_PROG_TYPE_LIRC_MODE2``. Once attached +to the LIRC device, this program will be called for each pulse, space or +timeout event on the LIRC device. The context for the BPF program is a +pointer to a unsigned int, which is a :ref:`LIRC_MODE_MODE2 <lirc-mode-mode2>` +value. When the program has decoded the scancode, it can be submitted using +the BPF functions ``bpf_rc_keydown()`` or ``bpf_rc_repeat()``. Mouse or pointer +movements can be reported using ``bpf_rc_pointer_rel()``. + +Once you have the file descriptor for the ``BPF_PROG_TYPE_LIRC_MODE2`` BPF +program, it can be attached to the LIRC device using the `bpf(2)`_ syscall. +The target must be the file descriptor for the LIRC device, and the +attach type must be ``BPF_LIRC_MODE2``. No more than 64 BPF programs can be +attached to a single LIRC device at a time. + +.. _bpf(2): http://man7.org/linux/man-pages/man2/bpf.2.html |