media: cec-pin-error-inj.rst: document CEC Pin Error Injection

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@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

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
 
 

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.