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diff --git a/extra/i2c_pseudo/Documentation.txt b/extra/i2c_pseudo/Documentation.txt deleted file mode 100644 index 77de99574b..0000000000 --- a/extra/i2c_pseudo/Documentation.txt +++ /dev/null @@ -1,291 +0,0 @@ -----Introduction---- - -Usually I2C adapters are implemented in a kernel driver. It is also possible to -implement an adapter in userspace, through the /dev/i2c-pseudo-controller -interface. Load module i2c-pseudo for this. - -Use cases for this module include: - -[A] Using local I2C device drivers, particularly i2c-dev, with I2C busses on -remote systems. For example, interacting with a Device Under Test (DUT) -connected to a Linux host through a debug interface, or interacting with a -remote host over a network. - -[B] Support I2C device driver tests that are too complex for the i2c-stub -module. For example, when simulating an I2C device where its driver might -issue a sequence of reads and writes without interruption, and the value a -certain address must change during the sequence. - -Any possible use case could of course be implemented as a kernel driver. -However, it can be much faster and easier to implement such things in userspace, -thanks to the far greater code reuse possibilities (libraries), the plethora of -programming language options for rapid iteration, and not needing to understand -how to implement Linux kernel drivers. - -This is not intended to replace kernel drivers for actual I2C busses on the -local host machine. - - - -----Details---- - -Each time /dev/i2c-pseudo-controller is opened, and the correct initialization -command is written to it (ADAPTER_START), a new I2C adapter is created. The -adapter will live until its file descriptor is closed. Multiple pseudo adapters -can co-exist simultaneously, controlled by the same or different userspace -processes. When an I2C device driver sends an I2C message to a pseudo adapter, -the message becomes readable from its file descriptor. If a reply is written -before the adapter timeout expires, that reply will be sent back to the I2C -device driver. - -Reads and writes are buffered inside i2c-pseudo such that userspace controllers -may split them up into arbitrarily small chunks. Multiple commands, or portions -of multiple commands, may be read or written together. - -Blocking I/O is the default. Non-blocking I/O is supported as well, enabled by -O_NONBLOCK. Polling is supported, with or without non-blocking I/O. A special -command (ADAPTER_SHUTDOWN) is available to unblock any pollers or blocked -reads or writes, as a convenience for a multi-threaded or multi-process program -that wants to exit. - -It is safe to access a single controller fd from multiple threads or processes -concurrently, though it is up to the controller to ensure proper ordering, and -to ensure that writes for different commands do not get interleaved. However, -it is recommended (not required) that controller implementations have only one -reader thread and one writer thread, which may or may not be the same thread. -Avoiding multiple readers and multiple writers greatly simplifies controller -implementation, and there is likely no performance benefit to be gained from -concurrent reads or concurrent writes due to how i2c-pseudo serializes them -internally. After all, on a real I2C bus only one I2C message can be active at -a time. - -Commands are newline-terminated, both those read from the controller device, and -those written to it. - - - -----Read Commands---- - -The commands that may be read from a pseudo controller device are: - - -Read Command: I2C_ADAPTER_NUM <num> -Example: "I2C_ADAPTER_NUM 5\n" - -Details: This is read in response to the GET_ADAPTER_NUM command being written. -The number is the I2C adapter number in decimal. This can only occur after -ADAPTER_START, because before that the number is not known and cannot be -predicted reliably. - - -Read Command: I2C_PSEUDO_ID <num> -Example: "I2C_PSEUDO_ID 98\n" - -Details: This is read in response to the GET_PSEUDO_ID command being written. -The number is the pseudo ID in decimal. - - -Read Command: I2C_BEGIN_XFER -Example: "I2C_BEGIN_XFER\n" - -Details: This indicates the start of an I2C transaction request, in other words -the start of the I2C messages from a single invocation of the I2C adapter's -master_xfer() callback. This can only occur after ADAPTER_START. - - -Read Command: I2C_XFER_REQ <xfer_id> <msg_id> <addr> <flags> <data_len> [<write_byte>[:...]] -Example: "I2C_XFER_REQ 3 0 0x0070 0x0000 2 AB:9F\n" -Example: "I2C_XFER_REQ 3 1 0x0070 0x0001 4\n" - -Details: This is a single I2C message that a device driver requested be sent on -the bus, in other words a single struct i2c_msg from master_xfer() msgs arg. - -The xfer_id is a number representing the whole I2C transaction, thus all -I2C_XFER_REQ between a I2C_BEGIN_XFER + I2C_COMMIT_XFER pair share an xfer_id. -The purpose is to ensure replies from the userspace controller are always -properly matched to the intended master_xfer() request. The first transaction -has xfer_id 0, and it increases by 1 with each transaction, however it will -eventually wrap back to 0 if enough transactions happen during the lifetime of a -pseudo adapter. It is guaranteed to have a large enough maximum value such that -there can never be multiple outstanding transactions with the same ID, due to an -internal limit in i2c-pseudo that will block master_xfer() calls when the -controller is falling behind in its replies. - -The msg_id is a decimal number representing the index of the I2C message within -its transaction, in other words the index in master_xfer() *msgs array arg. -This starts at 0 after each I2C_BEGIN_XFER. This is guaranteed to not wrap. - -The addr is the hexadecimal I2C address for this I2C message. The address is -right-aligned without any read/write bit. - -The flags are the same bitmask flags used in struct i2c_msg, in hexadecimal -form. Of particular importance to any pseudo controller is the read bit, which -is guaranteed to be 0x1 per Linux I2C documentation. - -The data_len is the decimal number of either how many bytes to write that will -follow, or how many bytes to read and reply with if this is a read request. - -If this is a read, data_len will be the final field in this command. If this is -a write, data_len will be followed by the given number of colon-separated -hexadecimal byte values, in the format shown in the example above. - - -Read Command: I2C_COMMIT_XFER -Example: "I2C_COMMIT_XFER\n" - -Details: This indicates the end of an I2C transaction request, in other words -the end of the I2C messages from a single invocation of the I2C adapter's -master_xfer() callback. This should be read exactly once after each -I2C_BEGIN_XFER, with a varying number of I2C_XFER_REQ between them. - - - -----Write Commands---- - -The commands that may be written to a pseudo controller device are: - - -Write Command: SET_ADAPTER_NAME_SUFFIX <suffix> -Example: "SET_ADAPTER_NAME_SUFFIX My Adapter\n" - -Details: Sets a suffix to append to the auto-generated I2C adapter name. Only -valid before ADAPTER_START. A space or other separator character will be placed -between the auto-generated name and the suffix, so there is no need to include a -leading separator in the suffix. If the resulting name is too long for the I2C -adapter name field, it will be quietly truncated. - - -Write Command: SET_ADAPTER_TIMEOUT_MS <ms> -Example: "SET_ADAPTER_TIMEOUT_MS 2000\n" - -Details: Sets the timeout in milliseconds for each I2C transaction, in other -words for each master_xfer() reply. Only valid before ADAPTER_START. The I2C -subsystem will automatically time out transactions based on this setting. Set -to 0 to use the I2C subsystem default timeout. The default timeout for new -pseudo adapters where this command has not been used is configurable at -i2c-pseudo module load time, and itself has a default independent from the I2C -subsystem default. (Though if the i2c-pseudo module level default is set to 0, -that has the same meaning as here.) - - -Write Command: ADAPTER_START -Example: "ADAPTER_START\n" - -Details: Tells i2c-pseudo to actually create the I2C adapter. Only valid once -per open controller fd. - - -Write Command: GET_ADAPTER_NUM -Example: "GET_ADAPTER_NUM\n" - -Details: Asks i2c-pseudo for the number assigned to this I2C adapter by the I2C -subsystem. Only valid after ADAPTER_START, because before that the number -is not known and cannot be predicted reliably. - - -Write Command: GET_PSEUDO_ID -Example: "GET_PSEUDO_ID\n" - -Details: Asks i2c-pseudo for the pseudo ID of this I2C adapter. The pseudo ID -will not be reused for the lifetime of the i2c-pseudo module, unless an internal -counter wraps. I2C clients can use this to track specific instances of pseudo -adapters, even when adapter numbers have been reused. - - -Write Command: I2C_XFER_REPLY <xfer_id> <msg_id> <addr> <flags> <errno> [<read_byte>[:...]] -Example: "I2C_XFER_REPLY 3 0 0x0070 0x0000 0\n" -Example: "I2C_XFER_REPLY 3 1 0x0070 0x0001 0 0B:29:02:D9\n" - -Details: This is how a pseudo controller can reply to I2C_XFER_REQ. Only valid -after I2C_XFER_REQ. A pseudo controller should write one of these for each -I2C_XFER_REQ it reads, including for failures, so that I2C device drivers need -not wait for the adapter timeout upon failure (if failure is known sooner). - -The fields in common with I2C_XFER_REQ have their same meanings, and their -values are expected to exactly match what was read in the I2C_XFER_REQ command -that this is in reply to. - -The errno field is how the pseudo controller indicates success or failure for -this I2C message. A 0 value indicates success. A non-zero value indicates a -failure. Pseudo controllers are encouraged to use errno values to encode some -meaning in a failure response, but that is not a requirement, and the I2C -adapter interface does not provide a way to pass per-message errno values to a -device driver anyways. - -Pseudo controllers are encouraged to reply in the same order as messages were -received, however i2c-pseudo will properly match up out-of-order replies with -their original requests. - - -Write Command: ADAPTER_SHUTDOWN -Example: "ADAPTER_SHUTDOWN\n" - -Details: This tells i2c-pseudo that the pseudo controller wants to shutdown and -intends to close the controller device fd soon. Use of this is OPTIONAL, it is -perfectly valid to close the controller device fd without ever using this -command. - -This commands unblocks any blocked controller I/O (reads, writes, or polls), and -that is its main purpose. - -Any I2C transactions attempted by a device driver after this command will fail, -and will not be passed on to the userspace controller. - -This DOES NOT delete the I2C adapter. Only closing the fd will do that. That -MAY CHANGE in the future, such that this does delete the I2C adapter. (However -this will never be required, it will always be okay to simply close the fd.) - - - -----Example userspace controller code---- - -In C, a simple exchange between i2c-pseudo and userspace might look like the -example below. Note that for brevity this lacks any error checking and -handling, which a real pseudo controller implementation should have. - -int fd; -char buf[1<<12]; - -fd = open("/dev/i2c-pseudo-controller", O_RDWR); -/* Create the I2C adapter. */ -dprintf(fd, "ADAPTER_START\n"); - -/* - * Pretend this I2C adapter number is 5, and the first I2C xfer sent to it was - * from this command (using its i2c-dev interface): - * $ i2cset -y 5 0x70 0xC2 - * - * Then this read would place the following into *buf: - * "I2C_BEGIN_XFER\n" - * "I2C_XFER_REQ 0 0 0x0070 0x0000 1 C2\n" - * "I2C_COMMIT_XFER\n" - */ -read(fd, buf, sizeof(buf)); - -/* This reply would allow the i2cset command above to exit successfully. */ -dprintf(fd, "I2C_XFER_REPLY 0 0 0x0070 0x0000 0\n"); - -/* - * Now pretend the next I2C xfer sent to this adapter was from: - * $ i2cget -y 5 0x70 0xAB - * - * Then this read would place the following into *buf: - * "I2C_BEGIN_XFER\n" - * "I2C_XFER_REQ 1 0 0x0070 0x0000 1 AB\n" - * "I2C_XFER_REQ 1 1 0x0070 0x0001 1\n'" - * "I2C_COMMIT_XFER\n" - */ -read(fd, buf, sizeof(buf)); - -/* - * These replies would allow the i2cget command above to print the following to - * stdout and exit successfully: - * 0x0b - * - * Note that it is also valid to write these together in one write(). - */ -dprintf(fd, "I2C_XFER_REPLY 1 0 0x0070 0x0000 0\n"); -dprintf(fd, "I2C_XFER_REPLY 1 1 0x0070 0x0001 0 0B\n"); - -/* Destroy the I2C adapter. */ -close(fd); |