From cf9610f9116d55c5a66ef9f1faecacabd93a9322 Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Mon, 24 Aug 2026 08:46:03 -0700 Subject: Merge tag 'pinctrl-v7.3-1' of git://git.kernel.org/pub/scm/linux/kernel/git/linusw/linux-pinctrl Pull pin control updates from Linus Walleij: "Core changes: - Use the non-blocking mux_state_try_select() in the generic MUX pin control back-end - Free pin maps on pinctrl_generic_to_map() failure in the core helpers New hardware pin control: - Qualcomm Maili TLMM SoC, PMG1110 PMIC, and Eliza LPASS LPI TLMM SoC (this is for the low power audio, LPASS = Low Power Audio SubSystem portions) - Upboard support on top of the Intel pin controller - Apple T6030 and T6031 support (just compatible strings) - Samsung Exynos 8855 SoC - Mediatek MT6858 SoC - Rockchip RK3308B and RV1106 SoCs - Airoha EN7523 and AN7563 SoCs Improvements: - Qualcomm TLMM GPIOs are unconditionally marked as wakeup capable - Qualcomm improvements on top of the Qualcomm PDC (power domain controller) irqchip improvements from tglx:s tree - Qualcomm IPQ806x and IPQ9650 non-urgent pin grop fixups - The NPCM8xx driver has been put into shape fixing many pin and group definitions - Some non-urgent Tegra 264 pin assignments are fixed up - Some non-urgent fixups to Airoha AN7581 and AN7583 registers and pin assignments, missing features etc" * tag 'pinctrl-v7.3-1' of git://git.kernel.org/pub/scm/linux/kernel/git/linusw/linux-pinctrl: (130 commits) dt-bindings: pinctrl: Convert TI DA850 pupd to DT schema pinctrl: meson: sync some modify from A4 pinctrl: meson: a4: Add input enable pin configuration pinctrl: realtek: rtd1625: remove unused group name spdif_sel pinctrl: realtek: rtd1625: fix base_bit for VE4 GPIO 13 dt-bindings: pinctrl: microchip,pic32mzda-pinctrl: Convert to DT schema Revert "Merge branch 'ib-rsk7204' into devel" pinctrl: rockchip: Add RV1106 pinctrl support dt-bindings: pinctrl: rockchip: Add RV1106 compatible pinctrl: rockchip: Decode drive strength in the get function pinctrl: fix PINCTRL_GENERIC_MUX not always being selectable pinctrl: airoha: add support of an7563 SoC dt-bindings: pinctrl: airoha: add support of an7563 pin controller pinctrl: airoha: try to find chip scu node by phandle first pinctrl: airoha: add support of en7523 SoC dt-bindings: pinctrl: airoha: add support of en7523 pin controller pinctrl: airoha: an7583: add support for olt pinmux pinctrl: airoha: an7583: add support for pon_alt pinmux pinctrl: airoha: an7583: add support for npu_uart pinmux dt-bindings: pinctrl: airoha: an7583: add missed features ... --- Documentation/i2c/dev-interface.rst | 221 ++++++++++++++++++++++++++++++++++++ 1 file changed, 221 insertions(+) create mode 100644 Documentation/i2c/dev-interface.rst (limited to 'Documentation/i2c/dev-interface.rst') diff --git a/Documentation/i2c/dev-interface.rst b/Documentation/i2c/dev-interface.rst new file mode 100644 index 000000000..c277a8e12 --- /dev/null +++ b/Documentation/i2c/dev-interface.rst @@ -0,0 +1,221 @@ +============================================ +Implementing I2C device drivers in userspace +============================================ + +Usually, I2C devices are controlled by a kernel driver. But it is also +possible to access all devices on an adapter from userspace, through +the /dev interface. You need to load module i2c-dev for this. + +Each registered I2C adapter gets a number, counting from 0. You can +examine /sys/class/i2c-dev/ to see what number corresponds to which adapter. +Alternatively, you can run "i2cdetect -l" to obtain a formatted list of all +I2C adapters present on your system at a given time. i2cdetect is part of +the i2c-tools package. + +I2C device files are character device files with major device number 89 +and a minor device number corresponding to the number assigned as +explained above. They should be called "i2c-%d" (i2c-0, i2c-1, ..., +i2c-10, ...). All 256 minor device numbers are reserved for I2C. + + +C example +========= + +So let's say you want to access an I2C adapter from a C program. +First, you need to include these two headers:: + + #include + #include + +Now, you have to decide which adapter you want to access. You should +inspect /sys/class/i2c-dev/ or run "i2cdetect -l" to decide this. +Adapter numbers are assigned somewhat dynamically, so you can not +assume much about them. They can even change from one boot to the next. + +Next thing, open the device file, as follows:: + + int file; + int adapter_nr = 2; /* probably dynamically determined */ + char filename[20]; + + snprintf(filename, 19, "/dev/i2c-%d", adapter_nr); + file = open(filename, O_RDWR); + if (file < 0) { + /* ERROR HANDLING; you can check errno to see what went wrong */ + exit(1); + } + +When you have opened the device, you must specify with what device +address you want to communicate:: + + int addr = 0x40; /* The I2C address */ + + if (ioctl(file, I2C_SLAVE, addr) < 0) { + /* ERROR HANDLING; you can check errno to see what went wrong */ + exit(1); + } + +Well, you are all set up now. You can now use SMBus commands or plain +I2C to communicate with your device. SMBus commands are preferred if +the device supports them. Both are illustrated below:: + + __u8 reg = 0x10; /* Device register to access */ + __s32 res; + char buf[10]; + + /* Using SMBus commands */ + res = i2c_smbus_read_word_data(file, reg); + if (res < 0) { + /* ERROR HANDLING: I2C transaction failed */ + } else { + /* res contains the read word */ + } + + /* + * Using I2C Write, equivalent of + * i2c_smbus_write_word_data(file, reg, 0x6543) + */ + buf[0] = reg; + buf[1] = 0x43; + buf[2] = 0x65; + if (write(file, buf, 3) != 3) { + /* ERROR HANDLING: I2C transaction failed */ + } + + /* Using I2C Read, equivalent of i2c_smbus_read_byte(file) */ + if (read(file, buf, 1) != 1) { + /* ERROR HANDLING: I2C transaction failed */ + } else { + /* buf[0] contains the read byte */ + } + +Note that only a subset of the I2C and SMBus protocols can be achieved by +the means of read() and write() calls. In particular, so-called combined +transactions (mixing read and write messages in the same transaction) +aren't supported. For this reason, this interface is almost never used by +user-space programs. + +IMPORTANT: because of the use of inline functions, you *have* to use +'-O' or some variation when you compile your program! + + +Full interface description +========================== + +The following IOCTLs are defined: + +``ioctl(file, I2C_SLAVE, long addr)`` + Change slave address. The address is passed in the 7 lower bits of the + argument (except for 10 bit addresses, passed in the 10 lower bits in this + case). + +``ioctl(file, I2C_TENBIT, long select)`` + Selects ten bit addresses if select not equals 0, selects normal 7 bit + addresses if select equals 0. Default 0. This request is only valid + if the adapter has I2C_FUNC_10BIT_ADDR. + +``ioctl(file, I2C_PEC, long select)`` + Selects SMBus PEC (packet error checking) generation and verification + if select not equals 0, disables if select equals 0. Default 0. + Used only for SMBus transactions. This request only has an effect if the + the adapter has I2C_FUNC_SMBUS_PEC; it is still safe if not, it just + doesn't have any effect. + +``ioctl(file, I2C_FUNCS, unsigned long *funcs)`` + Gets the adapter functionality and puts it in ``*funcs``. + +``ioctl(file, I2C_RDWR, struct i2c_rdwr_ioctl_data *msgset)`` + Do combined read/write transaction without stop in between. + Only valid if the adapter has I2C_FUNC_I2C. The argument is + a pointer to a:: + + struct i2c_rdwr_ioctl_data { + struct i2c_msg *msgs; /* ptr to array of simple messages */ + int nmsgs; /* number of messages to exchange */ + } + + The msgs[] themselves contain further pointers into data buffers. + The function will write or read data to or from that buffers depending + on whether the I2C_M_RD flag is set in a particular message or not. + The slave address and whether to use ten bit address mode has to be + set in each message, overriding the values set with the above ioctl's. + +``ioctl(file, I2C_SMBUS, struct i2c_smbus_ioctl_data *args)`` + If possible, use the provided ``i2c_smbus_*`` methods described below instead + of issuing direct ioctls. + +You can do plain I2C transactions by using read(2) and write(2) calls. +You do not need to pass the address byte; instead, set it through +ioctl I2C_SLAVE before you try to access the device. + +You can do SMBus level transactions (see documentation file smbus-protocol.rst +for details) through the following functions:: + + __s32 i2c_smbus_write_quick(int file, __u8 value); + __s32 i2c_smbus_read_byte(int file); + __s32 i2c_smbus_write_byte(int file, __u8 value); + __s32 i2c_smbus_read_byte_data(int file, __u8 command); + __s32 i2c_smbus_write_byte_data(int file, __u8 command, __u8 value); + __s32 i2c_smbus_read_word_data(int file, __u8 command); + __s32 i2c_smbus_write_word_data(int file, __u8 command, __u16 value); + __s32 i2c_smbus_process_call(int file, __u8 command, __u16 value); + __s32 i2c_smbus_block_process_call(int file, __u8 command, __u8 length, + __u8 *values); + __s32 i2c_smbus_read_block_data(int file, __u8 command, __u8 *values); + __s32 i2c_smbus_write_block_data(int file, __u8 command, __u8 length, + __u8 *values); + +All these transactions return -1 on failure; you can read errno to see +what happened. The 'write' transactions return 0 on success; the +'read' transactions return the read value, except for read_block, which +returns the number of values read. The block buffers need not be longer +than 32 bytes. + +The above functions are made available by linking against the libi2c library, +which is provided by the i2c-tools project. See: +https://git.kernel.org/pub/scm/utils/i2c-tools/i2c-tools.git/. + + +Implementation details +====================== + +For the interested, here's the code flow which happens inside the kernel +when you use the /dev interface to I2C: + +1) Your program opens /dev/i2c-N and calls ioctl() on it, as described in + section "C example" above. + +2) These open() and ioctl() calls are handled by the i2c-dev kernel + driver: see i2c-dev.c:i2cdev_open() and i2c-dev.c:i2cdev_ioctl(), + respectively. You can think of i2c-dev as a generic I2C chip driver + that can be programmed from user-space. + +3) Some ioctl() calls are for administrative tasks and are handled by + i2c-dev directly. Examples include I2C_SLAVE (set the address of the + device you want to access) and I2C_PEC (enable or disable SMBus error + checking on future transactions.) + +4) Other ioctl() calls are converted to in-kernel function calls by + i2c-dev. Examples include I2C_FUNCS, which queries the I2C adapter + functionality using i2c.h:i2c_get_functionality(), and I2C_SMBUS, which + performs an SMBus transaction using i2c-core-smbus.c:i2c_smbus_xfer(). + + The i2c-dev driver is responsible for checking all the parameters that + come from user-space for validity. After this point, there is no + difference between these calls that came from user-space through i2c-dev + and calls that would have been performed by kernel I2C chip drivers + directly. This means that I2C bus drivers don't need to implement + anything special to support access from user-space. + +5) These i2c.h functions are wrappers to the actual implementation of + your I2C bus driver. Each adapter must declare callback functions + implementing these standard calls. i2c.h:i2c_get_functionality() calls + i2c_adapter.algo->functionality(), while + i2c-core-smbus.c:i2c_smbus_xfer() calls either + adapter.algo->smbus_xfer() if it is implemented, or if not, + i2c-core-smbus.c:i2c_smbus_xfer_emulated() which in turn calls + i2c_adapter.algo->master_xfer(). + +After your I2C bus driver has processed these requests, execution runs +up the call chain, with almost no processing done, except by i2c-dev to +package the returned data, if any, in suitable format for the ioctl. -- cgit v1.3.1