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| author | Hans Verkuil <hverkuil-cisco@xs4all.nl> | 2023-03-27 10:32:01 +0200 |
|---|---|---|
| committer | Mauro Carvalho Chehab <mchehab@kernel.org> | 2023-04-15 08:49:01 +0200 |
| commit | 8eb2a208faa0635b355c753ed56440342c780850 (patch) | |
| tree | 3103a4e61b0d0b267e8b2263bb73a944241c8f03 /Documentation/admin-guide | |
| parent | media: cec: core: not all messages were passed on when monitoring (diff) | |
| download | linux-8eb2a208faa0635b355c753ed56440342c780850.tar.xz linux-8eb2a208faa0635b355c753ed56440342c780850.zip | |
media: Documentation: admin-guide: cec.rst: document NTP issue
The CEC pin framework is affected by NTP daemons speeding up or slowing
down the system clock. Document this and explain how to fix this for
chronyd.
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>
Diffstat (limited to 'Documentation/admin-guide')
| -rw-r--r-- | Documentation/admin-guide/media/cec.rst | 9 |
1 files changed, 9 insertions, 0 deletions
diff --git a/Documentation/admin-guide/media/cec.rst b/Documentation/admin-guide/media/cec.rst index 656dec7e0182..6b30e355cf23 100644 --- a/Documentation/admin-guide/media/cec.rst +++ b/Documentation/admin-guide/media/cec.rst @@ -55,6 +55,15 @@ Miscellaneous: you can control the CEC line through this driver. This supports error injection as well. +- cec-gpio and Allwinner A10 (or any other driver that uses the CEC pin + framework to drive the CEC pin directly): the CEC pin framework uses + high-resolution timers. These timers are affected by NTP daemons that + speed up or slow down the clock to sync with the official time. The + chronyd server will by default increase or decrease the clock by + 1/12th. This will cause the CEC timings to go out of spec. To fix this, + add a 'maxslewrate 40000' line to chronyd.conf. This limits the clock + frequency change to 1/25th, which keeps the CEC timings within spec. + Utilities ========= |