[PATCH 0/3] Improve latency of IR decoding

[Matthias Reichl]

Hi Sean,

On Wed, Mar 28, 2018 at 08:30:29PM +0200, Matthias Reichl wrote:
> Hi Sean,
> 
> On Sat, Mar 24, 2018 at 02:50:42PM +0000, Sean Young wrote:
> > The current IR decoding is much too slow. Many IR protocols rely on
> > a trailing space for decoding (e.g. rc-6 needs to know when the bits
> > end). The trailing space is generated by the IR timeout, and if this
> > is longer than required, keys can be perceived as sticky and slugish.
> > 
> > The other issue the keyup timer. IR has no concept of a keyup message,
> > this is implied by the absence of IR. So, minimising the timeout for
> > this further improves the handling.
> > 
> > With these patches in place, using IR with the builtin decoders is much
> > improved and feels very snappy.
> 
> thanks a lot for the patches!
> 
> I didn't have much time to test yet, but quick checks on
> Amlogic/meson-ir (kernel 4.16-rc7 + media tree + your patches)
> and Raspberry Pi (RPi foundation kernel 4.14 + my backport of
> your patches) look really promising.
> 
> I found one issue, though, in ir-sharp-decoder.c max_space must
> be set to SHARP_ECHO_SPACE - otherwise we get a timeout between
> the normal and inverted message part and decoding fails.
> 
> One thing I'm wondering is if the keyup timer marging might
> be too tight now. Basically we have just the fixed 10ms marging
> from idle timeout. The repeat periods of the protocols are rather
> accurate/strict, so (programmable) remotes not sticking to the
> official timing might cause repeated keyup/down events if they
> are repeating a tad to slow.
> 
> I'm not sure if this could be an issue, but maybe we should
> add a safety margin to the repeat periods as well? For example
> 10 or 20 percent of the specced repeat periods. What do you think?
> 
> To get some more test coverage I've asked my colleague to
> include my backport patch in the LibreELEC testbuilds for
> x86 and RPi. We've got some 500 regular users of these so if
> something's not working we should find out soon.

Quick update: testing so far went really smooth, no issues reported
since we included the backport patch in LibreELEC testbuilds.

Quote from https://github.com/LibreELEC/LibreELEC.tv/pull/2623#issuecomment-377897518
> This is in my nightly test builds since 28 March, and no problems reported so far.
>
> On my NUC with Harmony One/RC6 remote these commits are working just fine.

I've been using LibreELEC on RPi with the patch (using a gpio ir
receiver and a Hauppauge RC-5 remote) since then and everything
was fine as well.

so long,

Hias

> I just hope I
> didn't mess up the backport... Here's the link to my 4.14 patch:
> 
> https://github.com/HiassofT/LibreELEC.tv/blob/le9-ir-latency/packages/linux/patches/default/linux-999-improve-ir-timeout-handling.patch
> 
> so long & thanks,
> 
> Hias
> 
> > 
> > Sean Young (3):
> >   media: rc: set timeout to smallest value required by enabled protocols
> >   media: rc: add ioctl to get the current timeout
> >   media: rc: per-protocol repeat period and minimum keyup timer
> > 
> >  Documentation/media/uapi/rc/lirc-func.rst          |  1 +
> >  .../media/uapi/rc/lirc-set-rec-timeout.rst         | 14 +++--
> >  drivers/media/cec/cec-core.c                       |  2 +-
> >  drivers/media/rc/ir-imon-decoder.c                 |  1 +
> >  drivers/media/rc/ir-jvc-decoder.c                  |  1 +
> >  drivers/media/rc/ir-mce_kbd-decoder.c              |  1 +
> >  drivers/media/rc/ir-nec-decoder.c                  |  1 +
> >  drivers/media/rc/ir-rc5-decoder.c                  |  1 +
> >  drivers/media/rc/ir-rc6-decoder.c                  |  1 +
> >  drivers/media/rc/ir-sanyo-decoder.c                |  1 +
> >  drivers/media/rc/ir-sharp-decoder.c                |  1 +
> >  drivers/media/rc/ir-sony-decoder.c                 |  1 +
> >  drivers/media/rc/ir-xmp-decoder.c                  |  1 +
> >  drivers/media/rc/lirc_dev.c                        |  9 ++-
> >  drivers/media/rc/rc-core-priv.h                    |  1 +
> >  drivers/media/rc/rc-ir-raw.c                       | 31 +++++++++-
> >  drivers/media/rc/rc-main.c                         | 68 +++++++++++-----------
> >  include/uapi/linux/lirc.h                          |  6 ++
> >  18 files changed, 101 insertions(+), 41 deletions(-)
> > 
> > -- 
> > 2.14.3
> >