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diff --git a/Documentation/userspace-api/media/cec/cec-pin-error-inj.rst b/Documentation/userspace-api/media/cec/cec-pin-error-inj.rst new file mode 100644 index 000000000..064c8c5a1 --- /dev/null +++ b/Documentation/userspace-api/media/cec/cec-pin-error-inj.rst @@ -0,0 +1,327 @@ +.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later + +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. |