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1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later2 3.. _cec_pin_error_inj:4 5CEC Pin Framework Error Injection6=================================7 8The CEC Pin Framework is a core CEC framework for CEC hardware that only9has low-level support for the CEC bus. Most hardware today will have10high-level CEC support where the hardware deals with driving the CEC bus,11but some older devices aren't that fancy. However, this framework also12allows you to connect the CEC pin to a GPIO on e.g. a Raspberry Pi and13you have now made a CEC adapter.14 15What makes doing this so interesting is that since we have full control16over the bus it is easy to support error injection. This is ideal to17test how well CEC adapters can handle error conditions.18 19Currently only the cec-gpio driver (when the CEC line is directly20connected to a pull-up GPIO line) and the AllWinner A10/A20 drm driver21support this framework.22 23If ``CONFIG_CEC_PIN_ERROR_INJ`` is enabled, then error injection is available24through debugfs. Specifically, in ``/sys/kernel/debug/cec/cecX/`` there is25now an ``error-inj`` file.26 27.. note::28 29 The error injection commands are not a stable ABI and may change in the30 future.31 32With ``cat error-inj`` you can see both the possible commands and the current33error injection status::34 35 $ cat /sys/kernel/debug/cec/cec0/error-inj36 # Clear error injections:37 # clear clear all rx and tx error injections38 # rx-clear clear all rx error injections39 # tx-clear clear all tx error injections40 # <op> clear clear all rx and tx error injections for <op>41 # <op> rx-clear clear all rx error injections for <op>42 # <op> tx-clear clear all tx error injections for <op>43 #44 # RX error injection:45 # <op>[,<mode>] rx-nack NACK the message instead of sending an ACK46 # <op>[,<mode>] rx-low-drive <bit> force a low-drive condition at this bit position47 # <op>[,<mode>] rx-add-byte add a spurious byte to the received CEC message48 # <op>[,<mode>] rx-remove-byte remove the last byte from the received CEC message49 # any[,<mode>] rx-arb-lost [<poll>] generate a POLL message to trigger an arbitration lost50 #51 # TX error injection settings:52 # tx-ignore-nack-until-eom ignore early NACKs until EOM53 # tx-custom-low-usecs <usecs> define the 'low' time for the custom pulse54 # tx-custom-high-usecs <usecs> define the 'high' time for the custom pulse55 # tx-custom-pulse transmit the custom pulse once the bus is idle56 #57 # TX error injection:58 # <op>[,<mode>] tx-no-eom don't set the EOM bit59 # <op>[,<mode>] tx-early-eom set the EOM bit one byte too soon60 # <op>[,<mode>] tx-add-bytes <num> append <num> (1-255) spurious bytes to the message61 # <op>[,<mode>] tx-remove-byte drop the last byte from the message62 # <op>[,<mode>] tx-short-bit <bit> make this bit shorter than allowed63 # <op>[,<mode>] tx-long-bit <bit> make this bit longer than allowed64 # <op>[,<mode>] tx-custom-bit <bit> send the custom pulse instead of this bit65 # <op>[,<mode>] tx-short-start send a start pulse that's too short66 # <op>[,<mode>] tx-long-start send a start pulse that's too long67 # <op>[,<mode>] tx-custom-start send the custom pulse instead of the start pulse68 # <op>[,<mode>] tx-last-bit <bit> stop sending after this bit69 # <op>[,<mode>] tx-low-drive <bit> force a low-drive condition at this bit position70 #71 # <op> CEC message opcode (0-255) or 'any'72 # <mode> 'once' (default), 'always', 'toggle' or 'off'73 # <bit> CEC message bit (0-159)74 # 10 bits per 'byte': bits 0-7: data, bit 8: EOM, bit 9: ACK75 # <poll> CEC poll message used to test arbitration lost (0x00-0xff, default 0x0f)76 # <usecs> microseconds (0-10000000, default 1000)77 78 clear79 80You can write error injection commands to ``error-inj`` using81``echo 'cmd' >error-inj`` or ``cat cmd.txt >error-inj``. The ``cat error-inj``82output contains the current error commands. You can save the output to a file83and use it as an input to ``error-inj`` later.84 85Basic Syntax86------------87 88Leading spaces/tabs are ignored. If the next character is a ``#`` or the end89of the line was reached, then the whole line is ignored. Otherwise a command90is expected.91 92The error injection commands fall in two main groups: those relating to93receiving CEC messages and those relating to transmitting CEC messages. In94addition, there are commands to clear existing error injection commands and95to create custom pulses on the CEC bus.96 97Most error injection commands can be executed for specific CEC opcodes or for98all opcodes (``any``). Each command also has a 'mode' which can be ``off``99(can be used to turn off an existing error injection command), ``once``100(the default) which will trigger the error injection only once for the next101received or transmitted message, ``always`` to always trigger the error102injection and ``toggle`` to toggle the error injection on or off for every103transmit or receive.104 105So '``any rx-nack``' will NACK the next received CEC message,106'``any,always rx-nack``' will NACK all received CEC messages and107'``0x82,toggle rx-nack``' will only NACK if an Active Source message was108received and do that only for every other received message.109 110After an error was injected with mode ``once`` the error injection command111is cleared automatically, so ``once`` is a one-time deal.112 113All combinations of ``<op>`` and error injection commands can co-exist. So114this is fine::115 116 0x9e tx-add-bytes 1117 0x9e tx-early-eom118 0x9f tx-add-bytes 2119 any rx-nack120 121All four error injection commands will be active simultaneously.122 123However, if the same ``<op>`` and command combination is specified,124but with different arguments::125 126 0x9e tx-add-bytes 1127 0x9e tx-add-bytes 2128 129Then the second will overwrite the first.130 131Clear Error Injections132----------------------133 134``clear``135 Clear all error injections.136 137``rx-clear``138 Clear all receive error injections139 140``tx-clear``141 Clear all transmit error injections142 143``<op> clear``144 Clear all error injections for the given opcode.145 146``<op> rx-clear``147 Clear all receive error injections for the given opcode.148 149``<op> tx-clear``150 Clear all transmit error injections for the given opcode.151 152Receive Messages153----------------154 155``<op>[,<mode>] rx-nack``156 NACK broadcast messages and messages directed to this CEC adapter.157 Every byte of the message will be NACKed in case the transmitter158 keeps transmitting after the first byte was NACKed.159 160``<op>[,<mode>] rx-low-drive <bit>``161 Force a Low Drive condition at this bit position. If <op> specifies162 a specific CEC opcode then the bit position must be at least 18,163 otherwise the opcode hasn't been received yet. This tests if the164 transmitter can handle the Low Drive condition correctly and reports165 the error correctly. Note that a Low Drive in the first 4 bits can also166 be interpreted as an Arbitration Lost condition by the transmitter.167 This is implementation dependent.168 169``<op>[,<mode>] rx-add-byte``170 Add a spurious 0x55 byte to the received CEC message, provided171 the message was 15 bytes long or less. This is useful to test172 the high-level protocol since spurious bytes should be ignored.173 174``<op>[,<mode>] rx-remove-byte``175 Remove the last byte from the received CEC message, provided it176 was at least 2 bytes long. This is useful to test the high-level177 protocol since messages that are too short should be ignored.178 179``<op>[,<mode>] rx-arb-lost <poll>``180 Generate a POLL message to trigger an Arbitration Lost condition.181 This command is only allowed for ``<op>`` values of ``next`` or ``all``.182 As soon as a start bit has been received the CEC adapter will switch183 to transmit mode and it will transmit a POLL message. By default this is184 0x0f, but it can also be specified explicitly via the ``<poll>`` argument.185 186 This command can be used to test the Arbitration Lost condition in187 the remote CEC transmitter. Arbitration happens when two CEC adapters188 start sending a message at the same time. In that case the initiator189 with the most leading zeroes wins and the other transmitter has to190 stop transmitting ('Arbitration Lost'). This is very hard to test,191 except by using this error injection command.192 193 This does not work if the remote CEC transmitter has logical address194 0 ('TV') since that will always win.195 196Transmit Messages197-----------------198 199``tx-ignore-nack-until-eom``200 This setting changes the behavior of transmitting CEC messages. Normally201 as soon as the receiver NACKs a byte the transmit will stop, but the202 specification also allows that the full message is transmitted and only203 at the end will the transmitter look at the ACK bit. This is not204 recommended behavior since there is no point in keeping the CEC bus busy205 for longer than is strictly needed. Especially given how slow the bus is.206 207 This setting can be used to test how well a receiver deals with208 transmitters that ignore NACKs until the very end of the message.209 210``<op>[,<mode>] tx-no-eom``211 Don't set the EOM bit. Normally the last byte of the message has the EOM212 (End-Of-Message) bit set. With this command the transmit will just stop213 without ever sending an EOM. This can be used to test how a receiver214 handles this case. Normally receivers have a time-out after which215 they will go back to the Idle state.216 217``<op>[,<mode>] tx-early-eom``218 Set the EOM bit one byte too soon. This obviously only works for messages219 of two bytes or more. The EOM bit will be set for the second-to-last byte220 and not for the final byte. The receiver should ignore the last byte in221 this case. Since the resulting message is likely to be too short for this222 same reason the whole message is typically ignored. The receiver should be223 in Idle state after the last byte was transmitted.224 225``<op>[,<mode>] tx-add-bytes <num>``226 Append ``<num>`` (1-255) spurious bytes to the message. The extra bytes227 have the value of the byte position in the message. So if you transmit a228 two byte message (e.g. a Get CEC Version message) and add 2 bytes, then229 the full message received by the remote CEC adapter is230 ``0x40 0x9f 0x02 0x03``.231 232 This command can be used to test buffer overflows in the receiver. E.g.233 what does it do when it receives more than the maximum message size of 16234 bytes.235 236``<op>[,<mode>] tx-remove-byte``237 Drop the last byte from the message, provided the message is at least238 two bytes long. The receiver should ignore messages that are too short.239 240``<op>[,<mode>] tx-short-bit <bit>``241 Make this bit period shorter than allowed. The bit position cannot be242 an Ack bit. If <op> specifies a specific CEC opcode then the bit position243 must be at least 18, otherwise the opcode hasn't been received yet.244 Normally the period of a data bit is between 2.05 and 2.75 milliseconds.245 With this command the period of this bit is 1.8 milliseconds, this is246 done by reducing the time the CEC bus is high. This bit period is less247 than is allowed and the receiver should respond with a Low Drive248 condition.249 250 This command is ignored for 0 bits in bit positions 0 to 3. This is251 because the receiver also looks for an Arbitration Lost condition in252 those first four bits and it is undefined what will happen if it253 sees a too-short 0 bit.254 255``<op>[,<mode>] tx-long-bit <bit>``256 Make this bit period longer than is valid. The bit position cannot be257 an Ack bit. If <op> specifies a specific CEC opcode then the bit position258 must be at least 18, otherwise the opcode hasn't been received yet.259 Normally the period of a data bit is between 2.05 and 2.75 milliseconds.260 With this command the period of this bit is 2.9 milliseconds, this is261 done by increasing the time the CEC bus is high.262 263 Even though this bit period is longer than is valid it is undefined what264 a receiver will do. It might just accept it, or it might time out and265 return to Idle state. Unfortunately the CEC specification is silent about266 this.267 268 This command is ignored for 0 bits in bit positions 0 to 3. This is269 because the receiver also looks for an Arbitration Lost condition in270 those first four bits and it is undefined what will happen if it271 sees a too-long 0 bit.272 273``<op>[,<mode>] tx-short-start``274 Make this start bit period shorter than allowed. Normally the period of275 a start bit is between 4.3 and 4.7 milliseconds. With this command the276 period of the start bit is 4.1 milliseconds, this is done by reducing277 the time the CEC bus is high. This start bit period is less than is278 allowed and the receiver should return to Idle state when this is detected.279 280``<op>[,<mode>] tx-long-start``281 Make this start bit period longer than is valid. Normally the period of282 a start bit is between 4.3 and 4.7 milliseconds. With this command the283 period of the start bit is 5 milliseconds, this is done by increasing284 the time the CEC bus is high. This start bit period is more than is285 valid and the receiver should return to Idle state when this is detected.286 287 Even though this start bit period is longer than is valid it is undefined288 what a receiver will do. It might just accept it, or it might time out and289 return to Idle state. Unfortunately the CEC specification is silent about290 this.291 292``<op>[,<mode>] tx-last-bit <bit>``293 Just stop transmitting after this bit. If <op> specifies a specific CEC294 opcode then the bit position must be at least 18, otherwise the opcode295 hasn't been received yet. This command can be used to test how the receiver296 reacts when a message just suddenly stops. It should time out and go back297 to Idle state.298 299``<op>[,<mode>] tx-low-drive <bit>``300 Force a Low Drive condition at this bit position. If <op> specifies a301 specific CEC opcode then the bit position must be at least 18, otherwise302 the opcode hasn't been received yet. This can be used to test how the303 receiver handles Low Drive conditions. Note that if this happens at bit304 positions 0-3 the receiver can interpret this as an Arbitration Lost305 condition. This is implementation dependent.306 307Custom Pulses308-------------309 310``tx-custom-low-usecs <usecs>``311 This defines the duration in microseconds that the custom pulse pulls312 the CEC line low. The default is 1000 microseconds.313 314``tx-custom-high-usecs <usecs>``315 This defines the duration in microseconds that the custom pulse keeps the316 CEC line high (unless another CEC adapter pulls it low in that time).317 The default is 1000 microseconds. The total period of the custom pulse is318 ``tx-custom-low-usecs + tx-custom-high-usecs``.319 320``<op>[,<mode>] tx-custom-bit <bit>``321 Send the custom bit instead of a regular data bit. The bit position cannot322 be an Ack bit. If <op> specifies a specific CEC opcode then the bit323 position must be at least 18, otherwise the opcode hasn't been received yet.324 325``<op>[,<mode>] tx-custom-start``326 Send the custom bit instead of a regular start bit.327 328``tx-custom-pulse``329 Transmit a single custom pulse as soon as the CEC bus is idle.330