The CEC Pin framework adds support for Error Injection.
Document all the error injections commands and how to use it.
Signed-off-by: Hans Verkuil <hans.verkuil@xxxxxxxxx>
---
Changes since v2:
- replace '.. code-block:: none' by ::
- wrap to 80 columns
- move to uapi/cec
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Documentation/media/uapi/cec/cec-api.rst | 1 +
Documentation/media/uapi/cec/cec-pin-error-inj.rst | 325 +++++++++++++++++++++
2 files changed, 326 insertions(+)
create mode 100644 Documentation/media/uapi/cec/cec-pin-error-inj.rst
diff --git a/Documentation/media/uapi/cec/cec-api.rst b/Documentation/media/uapi/cec/cec-api.rst
index b68ca9c1d2e0..1e2cf498ba30 100644
--- a/Documentation/media/uapi/cec/cec-api.rst
+++ b/Documentation/media/uapi/cec/cec-api.rst
@@ -23,6 +23,7 @@ This part describes the CEC: Consumer Electronics Control
cec-intro
cec-funcs
+ cec-pin-error-inj
cec-header
diff --git a/Documentation/media/uapi/cec/cec-pin-error-inj.rst b/Documentation/media/uapi/cec/cec-pin-error-inj.rst
new file mode 100644
index 000000000000..464b006dbe0a
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+++ b/Documentation/media/uapi/cec/cec-pin-error-inj.rst
@@ -0,0 +1,325 @@
+CEC Pin Framework Error Injection
+=================================
+
+The CEC Pin Framework is a core CEC framework for CEC hardware that only
+has low-level support for the CEC bus. Most hardware today will have
+high-level CEC support where the hardware deals with driving the CEC bus,
+but some older devices aren't that fancy. However, this framework also
+allows you to connect the CEC pin to a GPIO on e.g. a Raspberry Pi and
+you have now made a CEC adapter.
+
+What makes doing this so interesting is that since we have full control
+over the bus it is easy to support error injection. This is ideal to
+test how well CEC adapters can handle error conditions.
+
+Currently only the cec-gpio driver (when the CEC line is directly
+connected to a pull-up GPIO line) and the AllWinner A10/A20 drm driver
+support this framework.
+
+If ``CONFIG_CEC_PIN_ERROR_INJ`` is enabled, then error injection is available
+through debugfs. Specifically, in ``/sys/kernel/debug/cec/cecX/`` there is
+now an ``error-inj`` file.
+
+.. note::
+
+ The error injection commands are not a stable ABI and may change in the
+ future.
+
+With ``cat error-inj`` you can see both the possible commands and the current
+error injection status::
+
+ $ cat /sys/kernel/debug/cec/cec0/error-inj
+ # Clear error injections:
+ # clear clear all rx and tx error injections
+ # rx-clear clear all rx error injections
+ # tx-clear clear all tx error injections
+ # <op> clear clear all rx and tx error injections for <op>
+ # <op> rx-clear clear all rx error injections for <op>
+ # <op> tx-clear clear all tx error injections for <op>
+ #
+ # 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
+ # <op>[,<mode>] rx-add-byte add a spurious byte to the received CEC message
+ # <op>[,<mode>] rx-remove-byte remove the last byte from the received CEC message
+ # <op>[,<mode>] rx-arb-lost <poll> generate a POLL message to trigger an arbitration lost
+ #
+ # TX error injection settings:
+ # tx-ignore-nack-until-eom ignore early NACKs until EOM
+ # 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 error injection:
+ # <op>[,<mode>] tx-no-eom don't set the EOM bit
+ # <op>[,<mode>] tx-early-eom set the EOM bit one byte too soon
+ # <op>[,<mode>] tx-add-bytes <num> append <num> (1-255) spurious bytes to the message
+ # <op>[,<mode>] tx-remove-byte drop the last byte from the message
+ # <op>[,<mode>] tx-short-bit <bit> make this bit shorter than allowed
+ # <op>[,<mode>] tx-long-bit <bit> make this bit longer than allowed
+ # <op>[,<mode>] tx-custom-bit <bit> send the custom pulse instead of this bit
+ # <op>[,<mode>] tx-short-start send a start pulse that's too short
+ # <op>[,<mode>] tx-long-start send a start pulse that's too long
+ # <op>[,<mode>] tx-custom-start send the custom pulse instead of the start pulse
+ # <op>[,<mode>] tx-last-bit <bit> stop sending after this bit
+ # <op>[,<mode>] tx-low-drive <bit> force a low-drive condition at this bit position
+ #
+ # <op> CEC message opcode (0-255) or 'any'
+ # <mode> 'once' (default), 'always', 'toggle' or 'off'
+ # <bit> CEC message bit (0-159)
+ # 10 bits per 'byte': bits 0-7: data, bit 8: EOM, bit 9: ACK
+ # <poll> CEC poll message used to test arbitration lost (0x00-0xff, default 0x0f)
+ # <usecs> microseconds (0-10000000, default 1000)
+
+ clear
+
+You can write error injection commands to ``error-inj`` using
+``echo 'cmd' >error-inj`` or ``cat cmd.txt >error-inj``. The ``cat error-inj``
+output contains the current error commands. You can save the output to a file
+and use it as an input to ``error-inj`` later.
+
+Basic Syntax
+------------
+
+Leading spaces/tabs are ignored. If the next character is a ``#`` or the end
+of the line was reached, then the whole line is ignored. Otherwise a command
+is expected.
+
+The error injection commands fall in two main groups: those relating to
+receiving CEC messages and those relating to transmitting CEC messages. In
+addition, there are commands to clear existing error injection commands and
+to create custom pulses on the CEC bus.
+
+Most error injection commands can be executed for specific CEC opcodes or for
+all opcodes (``any``). Each command also has a 'mode' which can be ``off``
+(can be used to turn off an existing error injection command), ``once``
+(the default) which will trigger the error injection only once for the next
+received or transmitted message, ``always`` to always trigger the error
+injection and ``toggle`` to toggle the error injection on or off for every
+transmit or receive.
+
+So '``any rx-nack``' will NACK the next received CEC message,
+'``any,always rx-nack``' will NACK all received CEC messages and
+'``0x82,toggle rx-nack``' will only NACK if an Active Source message was
+received and do that only for every other received message.
+
+After an error was injected with mode ``once`` the error injection command
+is cleared automatically, so ``once`` is a one-time deal.
+
+All combinations of ``<op>`` and error injection commands can co-exist. So
+this is fine::
+
+ 0x9e tx-add-bytes 1
+ 0x9e tx-early-eom
+ 0x9f tx-add-bytes 2
+ any rx-nack
+
+All four error injection commands will be active simultaneously.
+
+However, if the same ``<op>`` and command combination is specified,
+but with different arguments::
+
+ 0x9e tx-add-bytes 1
+ 0x9e tx-add-bytes 2
+
+Then the second will overwrite the first.
+
+Clear Error Injections
+----------------------
+
+``clear``
+ Clear all error injections.
+
+``rx-clear``
+ Clear all receive error injections
+
+``tx-clear``
+ Clear all transmit error injections
+
+``<op> clear``
+ Clear all error injections for the given opcode.
+
+``<op> rx-clear``
+ Clear all receive error injections for the given opcode.
+
+``<op> tx-clear``
+ Clear all transmit error injections for the given opcode.
+
+Receive Messages
+----------------
+
+``<op>[,<mode>] rx-nack``
+ NACK broadcast messages and messages directed to this CEC adapter.
+ Every byte of the message will be NACKed in case the transmitter
+ keeps transmitting after the first byte was NACKed.
+
+``<op>[,<mode>] rx-low-drive <bit>``
+ Force a Low Drive condition at this bit position. If <op> specifies
+ a specific CEC opcode then the bit position must be at least 18,
+ otherwise the opcode hasn't been received yet. This tests if the
+ transmitter can handle the Low Drive condition correctly and reports
+ the error correctly. Note that a Low Drive in the first 4 bits can also
+ be interpreted as an Arbitration Lost condition by the transmitter.
+ This is implementation dependent.
+
+``<op>[,<mode>] rx-add-byte``
+ Add a spurious 0x55 byte to the received CEC message, provided
+ the message was 15 bytes long or less. This is useful to test
+ the high-level protocol since spurious bytes should be ignored.
+
+``<op>[,<mode>] rx-remove-byte``
+ Remove the last byte from the received CEC message, provided it
+ was at least 2 bytes long. This is useful to test the high-level
+ protocol since messages that are too short should be ignored.
+
+``<op>[,<mode>] rx-arb-lost <poll>``
+ Generate a POLL message to trigger an Arbitration Lost condition.
+ This command is only allowed for ``<op>`` values of ``next`` or ``all``.
+ As soon as a start bit has been received the CEC adapter will switch
+ to transmit mode and it will transmit a POLL message. By default this is
+ 0x0f, but it can also be specified explicitly via the ``<poll>`` argument.
+
+ This command can be used to test the Arbitration Lost condition in
+ the remote CEC transmitter. Arbitration happens when two CEC adapters
+ start sending a message at the same time. In that case the initiator
+ with the most leading zeroes wins and the other transmitter has to
+ stop transmitting ('Arbitration Lost'). This is very hard to test,
+ except by using this error injection command.
+
+ This does not work if the remote CEC transmitter has logical address
+ 0 ('TV') since that will always win.
+
+Transmit Messages
+-----------------
+
+``tx-ignore-nack-until-eom``
+ This setting changes the behavior of transmitting CEC messages. Normally
+ as soon as the receiver NACKs a byte the transmit will stop, but the
+ specification also allows that the full message is transmitted and only
+ at the end will the transmitter look at the ACK bit. This is not
+ recommended behavior since there is no point in keeping the CEC bus busy
+ for longer than is strictly needed. Especially given how slow the bus is.
+
+ This setting can be used to test how well a receiver deals with
+ transmitters that ignore NACKs until the very end of the message.
+
+``<op>[,<mode>] tx-no-eom``
+ Don't set the EOM bit. Normally the last byte of the message has the EOM
+ (End-Of-Message) bit set. With this command the transmit will just stop
+ without ever sending an EOM. This can be used to test how a receiver
+ handles this case. Normally receivers have a time-out after which
+ they will go back to the Idle state.
+
+``<op>[,<mode>] tx-early-eom``
+ Set the EOM bit one byte too soon. This obviously only works for messages
+ of two bytes or more. The EOM bit will be set for the second-to-last byte
+ and not for the final byte. The receiver should ignore the last byte in
+ this case. Since the resulting message is likely to be too short for this
+ same reason the whole message is typically ignored. The receiver should be
+ in Idle state after the last byte was transmitted.
+
+``<op>[,<mode>] tx-add-bytes <num>``
+ Append ``<num>`` (1-255) spurious bytes to the message. The extra bytes
+ have the value of the byte position in the message. So if you transmit a
+ two byte message (e.g. a Get CEC Version message) and add 2 bytes, then
+ the full message received by the remote CEC adapter is
+ ``0x40 0x9f 0x02 0x03``.
+
+ This command can be used to test buffer overflows in the receiver. E.g.
+ what does it do when it receives more than the maximum message size of 16
+ bytes.
+
+``<op>[,<mode>] tx-remove-byte``
+ Drop the last byte from the message, provided the message is at least
+ two bytes long. The receiver should ignore messages that are too short.
+
+``<op>[,<mode>] tx-short-bit <bit>``
+ Make this bit period shorter than allowed. The bit position cannot be
+ an Ack bit. If <op> specifies a specific CEC opcode then the bit position
+ must be at least 18, otherwise the opcode hasn't been received yet.
+ Normally the period of a data bit is between 2.05 and 2.75 milliseconds.
+ With this command the period of this bit is 1.8 milliseconds, this is
+ done by reducing the time the CEC bus is high. This bit period is less
+ than is allowed and the receiver should respond with a Low Drive
+ condition.
+
+ This command is ignored for 0 bits in bit positions 0 to 3. This is
+ because the receiver also looks for an Arbitration Lost condition in
+ those first four bits and it is undefined what will happen if it
+ sees a too-short 0 bit.
+
+``<op>[,<mode>] tx-long-bit <bit>``
+ Make this bit period longer than is valid. The bit position cannot be
+ an Ack bit. If <op> specifies a specific CEC opcode then the bit position
+ must be at least 18, otherwise the opcode hasn't been received yet.
+ Normally the period of a data bit is between 2.05 and 2.75 milliseconds.
+ With this command the period of this bit is 2.9 milliseconds, this is
+ done by increasing the time the CEC bus is high.
+
+ Even though this bit period is longer than is valid it is undefined what
+ a receiver will do. It might just accept it, or it might time out and
+ return to Idle state. Unfortunately the CEC specification is silent about
+ this.
+
+ This command is ignored for 0 bits in bit positions 0 to 3. This is
+ because the receiver also looks for an Arbitration Lost condition in
+ those first four bits and it is undefined what will happen if it
+ sees a too-long 0 bit.
+
+``<op>[,<mode>] tx-short-start``
+ Make this start bit period shorter than allowed. Normally the period of
+ a start bit is between 4.3 and 4.7 milliseconds. With this command the
+ period of the start bit is 4.1 milliseconds, this is done by reducing
+ the time the CEC bus is high. This start bit period is less than is
+ allowed and the receiver should return to Idle state when this is detected.
+
+``<op>[,<mode>] tx-long-start``
+ Make this start bit period longer than is valid. Normally the period of
+ a start bit is between 4.3 and 4.7 milliseconds. With this command the
+ period of the start bit is 5 milliseconds, this is done by increasing
+ the time the CEC bus is high. This start bit period is more than is
+ valid and the receiver should return to Idle state when this is detected.
+
+ Even though this start bit period is longer than is valid it is undefined
+ what a receiver will do. It might just accept it, or it might time out and
+ return to Idle state. Unfortunately the CEC specification is silent about
+ this.
+
+``<op>[,<mode>] tx-last-bit <bit>``
+ Just stop transmitting after this bit. If <op> specifies a specific CEC
+ opcode then the bit position must be at least 18, otherwise the opcode
+ hasn't been received yet. This command can be used to test how the receiver
+ reacts when a message just suddenly stops. It should time out and go back
+ to Idle state.
+
+``<op>[,<mode>] tx-low-drive <bit>``
+ Force a Low Drive condition at this bit position. If <op> specifies a
+ specific CEC opcode then the bit position must be at least 18, otherwise
+ the opcode hasn't been received yet. This can be used to test how the
+ receiver handles Low Drive conditions. Note that if this happens at bit
+ positions 0-3 the receiver can interpret this as an Arbitration Lost
+ condition. This is implementation dependent.
+
+Custom Pulses
+-------------
+
+``tx-custom-low-usecs <usecs>``
+ This defines the duration in microseconds that the custom pulse pulls
+ the CEC line low. The default is 1000 microseconds.
+
+``tx-custom-high-usecs <usecs>``
+ This defines the duration in microseconds that the custom pulse keeps the
+ CEC line high (unless another CEC adapter pulls it low in that time).
+ The default is 1000 microseconds. The total period of the custom pulse is
+ ``tx-custom-low-usecs + tx-custom-high-usecs``.
+
+``<op>[,<mode>] tx-custom-bit <bit>``
+ Send the custom bit instead of a regular data bit. The bit position cannot
+ be an Ack bit. If <op> specifies a specific CEC opcode then the bit
+ position must be at least 18, otherwise the opcode hasn't been received yet.
+
+``<op>[,<mode>] tx-custom-start``
+ Send the custom bit instead of a regular start bit.
+
+``tx-custom-pulse``
+ Transmit a single custom pulse as soon as the CEC bus is idle.
--
2.15.1
