On Mon Jun 30 13:08:48 2025 +0200, Hans Verkuil wrote:
> Document rx-no-low-drive and the new support to inject
> glitches.
>
> Signed-off-by: Hans Verkuil <hverk...@xs4all.nl>
> Signed-off-by: Mauro Carvalho Chehab <mchehab+hua...@kernel.org>
Patch committed.
Thanks,
Mauro Carvalho Chehab
.../userspace-api/media/cec/cec-pin-error-inj.rst | 42 ++++++++++++++++++++++
1 file changed, 42 insertions(+)
---
diff --git a/Documentation/userspace-api/media/cec/cec-pin-error-inj.rst
b/Documentation/userspace-api/media/cec/cec-pin-error-inj.rst
index 411d42a742f3..c02790319f3f 100644
--- a/Documentation/userspace-api/media/cec/cec-pin-error-inj.rst
+++ b/Documentation/userspace-api/media/cec/cec-pin-error-inj.rst
@@ -41,6 +41,9 @@ error injection status::
# <op> rx-clear clear all rx error injections for <op>
# <op> tx-clear clear all tx error injections for <op>
#
+ # RX error injection settings:
+ # rx-no-low-drive do not generate low-drive pulses
+ #
# RX error injection:
# <op>[,<mode>] rx-nack NACK the message instead of
sending an ACK
# <op>[,<mode>] rx-low-drive <bit> force a low-drive condition at
this bit position
@@ -53,6 +56,10 @@ error injection status::
# tx-custom-low-usecs <usecs> define the 'low' time for the
custom pulse
# tx-custom-high-usecs <usecs> define the 'high' time for the
custom pulse
# tx-custom-pulse transmit the custom pulse once
the bus is idle
+ # tx-glitch-low-usecs <usecs> define the 'low' time for the
glitch pulse
+ # tx-glitch-high-usecs <usecs> define the 'high' time for the
glitch pulse
+ # tx-glitch-falling-edge send the glitch pulse after
every falling edge
+ # tx-glitch-rising-edge send the glitch pulse after
every rising edge
#
# TX error injection:
# <op>[,<mode>] tx-no-eom don't set the EOM bit
@@ -193,6 +200,14 @@ Receive Messages
This does not work if the remote CEC transmitter has logical address
0 ('TV') since that will always win.
+``rx-no-low-drive``
+ The receiver will ignore situations that would normally generate a
+ Low Drive pulse (3.6 ms). This is typically done if a spurious pulse is
+ detected when receiving a message, and it indicates to the transmitter that
+ the message has to be retransmitted since the receiver got confused.
+ Disabling this is useful to test how other CEC devices handle glitches
+ by ensuring we will not be the one that generates a Low Drive.
+
Transmit Messages
-----------------
@@ -327,3 +342,30 @@ Custom Pulses
``tx-custom-pulse``
Transmit a single custom pulse as soon as the CEC bus is idle.
+
+Glitch Pulses
+-------------
+
+This emulates what happens if the signal on the CEC line is seeing spurious
+pulses. Typically this happens after the falling or rising edge where there
+is a short voltage fluctuation that, if the CEC hardware doesn't do
+deglitching, can be seen as a spurious pulse and can cause a Low Drive
+condition or corrupt data.
+
+``tx-glitch-low-usecs <usecs>``
+ This defines the duration in microseconds that the glitch pulse pulls
+ the CEC line low. The default is 1 microsecond. The range is 0-100
+ microseconds. If 0, then no glitch pulse will be generated.
+
+``tx-glitch-high-usecs <usecs>``
+ This defines the duration in microseconds that the glitch pulse keeps the
+ CEC line high (unless another CEC adapter pulls it low in that time).
+ The default is 1 microseconds. The range is 0-100 microseconds. If 0, then
+ no glitch pulse will be generated.The total period of the glitch pulse is
+ ``tx-custom-low-usecs + tx-custom-high-usecs``.
+
+``tx-glitch-falling-edge``
+ Send the glitch pulse right after the falling edge.
+
+``tx-glitch-rising-edge``
+ Send the glitch pulse right after the rising edge.
