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@xxxxxxxxx> --- 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 =========
