diff options
Diffstat (limited to 'Documentation/i2c')
| -rw-r--r-- | Documentation/i2c/busses/i2c-parport-light.rst | 24 | ||||
| -rw-r--r-- | Documentation/i2c/busses/index.rst | 1 | ||||
| -rw-r--r-- | Documentation/i2c/dev-interface.rst | 24 | ||||
| -rw-r--r-- | Documentation/i2c/dma-considerations.rst | 2 | ||||
| -rw-r--r-- | Documentation/i2c/i2c-protocol.rst | 45 | ||||
| -rw-r--r-- | Documentation/i2c/i2c-topology.rst | 72 | ||||
| -rw-r--r-- | Documentation/i2c/i2c.svg | 1341 | ||||
| -rw-r--r-- | Documentation/i2c/index.rst | 58 | ||||
| -rw-r--r-- | Documentation/i2c/instantiating-devices.rst | 123 | ||||
| -rw-r--r-- | Documentation/i2c/old-module-parameters.rst | 31 | ||||
| -rw-r--r-- | Documentation/i2c/slave-interface.rst | 4 | ||||
| -rw-r--r-- | Documentation/i2c/smbus-protocol.rst | 107 | ||||
| -rw-r--r-- | Documentation/i2c/summary.rst | 62 | ||||
| -rw-r--r-- | Documentation/i2c/writing-clients.rst | 36 |
14 files changed, 1667 insertions, 263 deletions
diff --git a/Documentation/i2c/busses/i2c-parport-light.rst b/Documentation/i2c/busses/i2c-parport-light.rst deleted file mode 100644 index e73af975d2c8..000000000000 --- a/Documentation/i2c/busses/i2c-parport-light.rst +++ /dev/null @@ -1,24 +0,0 @@ -=============================== -Kernel driver i2c-parport-light -=============================== - -Author: Jean Delvare <jdelvare@suse.de> - -This driver is a light version of i2c-parport. It doesn't depend -on the parport driver, and uses direct I/O access instead. This might be -preferred on embedded systems where wasting memory for the clean but heavy -parport handling is not an option. The drawback is a reduced portability -and the impossibility to daisy-chain other parallel port devices. - -Please see i2c-parport for documentation. - -Module parameters: - -* type: type of adapter (see i2c-parport or modinfo) - -* base: base I/O address - Default is 0x378 which is fairly common for parallel ports, at least on PC. - -* irq: optional IRQ - This must be passed if you want SMBus alert support, assuming your adapter - actually supports this. diff --git a/Documentation/i2c/busses/index.rst b/Documentation/i2c/busses/index.rst index 2a26e251a335..5e4077b08d86 100644 --- a/Documentation/i2c/busses/index.rst +++ b/Documentation/i2c/busses/index.rst @@ -20,7 +20,6 @@ I2C Bus Drivers i2c-nforce2 i2c-nvidia-gpu i2c-ocores - i2c-parport-light i2c-parport i2c-pca-isa i2c-piix4 diff --git a/Documentation/i2c/dev-interface.rst b/Documentation/i2c/dev-interface.rst index 69c23a3c2b1b..bdb247f2f11a 100644 --- a/Documentation/i2c/dev-interface.rst +++ b/Documentation/i2c/dev-interface.rst @@ -1,27 +1,27 @@ -==================== -I2C Device Interface -==================== +============================================ +Implementing I2C device drivers in userspace +============================================ -Usually, i2c devices are controlled by a kernel driver. But it is also +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 +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 +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. +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. +So let's say you want to access an I2C adapter from a C program. First, you need to include these two headers:: #include <linux/i2c-dev.h> @@ -66,7 +66,7 @@ the device supports them. Both are illustrated below:: /* Using SMBus commands */ res = i2c_smbus_read_word_data(file, reg); if (res < 0) { - /* ERROR HANDLING: i2c transaction failed */ + /* ERROR HANDLING: I2C transaction failed */ } else { /* res contains the read word */ } @@ -79,12 +79,12 @@ the device supports them. Both are illustrated below:: buf[1] = 0x43; buf[2] = 0x65; if (write(file, buf, 3) != 3) { - /* ERROR HANDLING: i2c transaction failed */ + /* 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 */ + /* ERROR HANDLING: I2C transaction failed */ } else { /* buf[0] contains the read byte */ } @@ -144,7 +144,7 @@ The following IOCTLs are defined: 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 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. diff --git a/Documentation/i2c/dma-considerations.rst b/Documentation/i2c/dma-considerations.rst index 203002054120..142d52ce9ebb 100644 --- a/Documentation/i2c/dma-considerations.rst +++ b/Documentation/i2c/dma-considerations.rst @@ -2,7 +2,7 @@ Linux I2C and DMA ================= -Given that i2c is a low-speed bus, over which the majority of messages +Given that I2C is a low-speed bus, over which the majority of messages transferred are small, it is not considered a prime user of DMA access. At this time of writing, only 10% of I2C bus master drivers have DMA support implemented. And the vast majority of transactions are so small that setting up diff --git a/Documentation/i2c/i2c-protocol.rst b/Documentation/i2c/i2c-protocol.rst index 2f8fcf671b2e..b2092f8f815d 100644 --- a/Documentation/i2c/i2c-protocol.rst +++ b/Documentation/i2c/i2c-protocol.rst @@ -1,26 +1,26 @@ -============ -I2C Protocol -============ +================ +The I2C Protocol +================ -This document describes the i2c protocol. Or will, when it is finished :-) +This document describes the I2C protocol. Or will, when it is finished :-) Key to symbols ============== =============== ============================================================= -S (1 bit) : Start bit -P (1 bit) : Stop bit -Rd/Wr (1 bit) : Read/Write bit. Rd equals 1, Wr equals 0. -A, NA (1 bit) : Accept and reverse accept bit. -Addr (7 bits): I2C 7 bit address. Note that this can be expanded as usual to +S Start condition +P Stop condition +Rd/Wr (1 bit) Read/Write bit. Rd equals 1, Wr equals 0. +A, NA (1 bit) Acknowledge (ACK) and Not Acknowledge (NACK) bit +Addr (7 bits) I2C 7 bit address. Note that this can be expanded as usual to get a 10 bit I2C address. -Comm (8 bits): Command byte, a data byte which often selects a register on +Comm (8 bits) Command byte, a data byte which often selects a register on the device. -Data (8 bits): A plain data byte. Sometimes, I write DataLow, DataHigh +Data (8 bits) A plain data byte. Sometimes, I write DataLow, DataHigh for 16 bit data. -Count (8 bits): A data byte containing the length of a block operation. +Count (8 bits) A data byte containing the length of a block operation. -[..]: Data sent by I2C device, as opposed to data sent by the +[..] Data sent by I2C device, as opposed to data sent by the host adapter. =============== ============================================================= @@ -28,7 +28,7 @@ Count (8 bits): A data byte containing the length of a block operation. Simple send transaction ======================= -This corresponds to i2c_master_send:: +Implemented by i2c_master_send():: S Addr Wr [A] Data [A] Data [A] ... [A] Data [A] P @@ -36,7 +36,7 @@ This corresponds to i2c_master_send:: Simple receive transaction ========================== -This corresponds to i2c_master_recv:: +Implemented by i2c_master_recv():: S Addr Rd [A] [Data] A [Data] A ... A [Data] NA P @@ -44,11 +44,11 @@ This corresponds to i2c_master_recv:: Combined transactions ===================== -This corresponds to i2c_transfer +Implemented by i2c_transfer(). -They are just like the above transactions, but instead of a stop bit P -a start bit S is sent and the transaction continues. An example of -a byte read, followed by a byte write:: +They are just like the above transactions, but instead of a stop +condition P a start condition S is sent and the transaction continues. +An example of a byte read, followed by a byte write:: S Addr Rd [A] [Data] NA S Addr Wr [A] Data [A] P @@ -57,7 +57,7 @@ Modified transactions ===================== The following modifications to the I2C protocol can also be generated by -setting these flags for i2c messages. With the exception of I2C_M_NOSTART, they +setting these flags for I2C messages. With the exception of I2C_M_NOSTART, they are usually only needed to work around device issues: I2C_M_IGNORE_NAK: @@ -77,8 +77,9 @@ I2C_M_NOSTART: S Addr Rd [A] [Data] NA Data [A] P If you set the I2C_M_NOSTART variable for the first partial message, - we do not generate Addr, but we do generate the startbit S. This will - probably confuse all other clients on your bus, so don't try this. + we do not generate Addr, but we do generate the start condition S. + This will probably confuse all other clients on your bus, so don't + try this. This is often used to gather transmits from multiple data buffers in system memory into something that appears as a single transfer to the diff --git a/Documentation/i2c/i2c-topology.rst b/Documentation/i2c/i2c-topology.rst index 0c1ae95f6a97..7cb53819778e 100644 --- a/Documentation/i2c/i2c-topology.rst +++ b/Documentation/i2c/i2c-topology.rst @@ -1,9 +1,9 @@ -============ -I2C topology -============ +================================ +I2C muxes and complex topologies +================================ -There are a couple of reasons for building more complex i2c topologies -than a straight-forward i2c bus with one adapter and one or more devices. +There are a couple of reasons for building more complex I2C topologies +than a straight-forward I2C bus with one adapter and one or more devices. 1. A mux may be needed on the bus to prevent address collisions. @@ -11,20 +11,20 @@ than a straight-forward i2c bus with one adapter and one or more devices. may be needed to determine if it is ok to access the bus. 3. A device (particularly RF tuners) may want to avoid the digital noise - from the i2c bus, at least most of the time, and sits behind a gate + from the I2C bus, at least most of the time, and sits behind a gate that has to be operated before the device can be accessed. Etc === -These constructs are represented as i2c adapter trees by Linux, where +These constructs are represented as I2C adapter trees by Linux, where each adapter has a parent adapter (except the root adapter) and zero or more child adapters. The root adapter is the actual adapter that issues -i2c transfers, and all adapters with a parent are part of an "i2c-mux" +I2C transfers, and all adapters with a parent are part of an "i2c-mux" object (quoted, since it can also be an arbitrator or a gate). Depending of the particular mux driver, something happens when there is -an i2c transfer on one of its child adapters. The mux driver can +an I2C transfer on one of its child adapters. The mux driver can obviously operate a mux, but it can also do arbitration with an external bus master or open a gate. The mux driver has two operations for this, select and deselect. select is called before the transfer and (the @@ -34,7 +34,7 @@ optional) deselect is called after the transfer. Locking ======= -There are two variants of locking available to i2c muxes, they can be +There are two variants of locking available to I2C muxes, they can be mux-locked or parent-locked muxes. As is evident from below, it can be useful to know if a mux is mux-locked or if it is parent-locked. The following list was correct at the time of writing: @@ -45,7 +45,7 @@ In drivers/i2c/muxes/: i2c-arb-gpio-challenge Parent-locked i2c-mux-gpio Normally parent-locked, mux-locked iff all involved gpio pins are controlled by the - same i2c root adapter that they mux. + same I2C root adapter that they mux. i2c-mux-gpmux Normally parent-locked, mux-locked iff specified in device-tree. i2c-mux-ltc4306 Mux-locked @@ -54,7 +54,7 @@ i2c-mux-pca9541 Parent-locked i2c-mux-pca954x Parent-locked i2c-mux-pinctrl Normally parent-locked, mux-locked iff all involved pinctrl devices are controlled - by the same i2c root adapter that they mux. + by the same I2C root adapter that they mux. i2c-mux-reg Parent-locked ====================== ============================================= @@ -83,9 +83,9 @@ Mux-locked muxes Mux-locked muxes does not lock the entire parent adapter during the full select-transfer-deselect transaction, only the muxes on the parent adapter are locked. Mux-locked muxes are mostly interesting if the -select and/or deselect operations must use i2c transfers to complete +select and/or deselect operations must use I2C transfers to complete their tasks. Since the parent adapter is not fully locked during the -full transaction, unrelated i2c transfers may interleave the different +full transaction, unrelated I2C transfers may interleave the different stages of the transaction. This has the benefit that the mux driver may be easier and cleaner to implement, but it has some caveats. @@ -109,14 +109,14 @@ ML2. It is not safe to build arbitrary topologies with two (or more) ML3. A mux-locked mux cannot be used by a driver for auto-closing gates/muxes, i.e. something that closes automatically after a given - number (one, in most cases) of i2c transfers. Unrelated i2c transfers + number (one, in most cases) of I2C transfers. Unrelated I2C transfers may creep in and close prematurely. -ML4. If any non-i2c operation in the mux driver changes the i2c mux state, +ML4. If any non-I2C operation in the mux driver changes the I2C mux state, the driver has to lock the root adapter during that operation. Otherwise garbage may appear on the bus as seen from devices - behind the mux, when an unrelated i2c transfer is in flight during - the non-i2c mux-changing operation. + behind the mux, when an unrelated I2C transfer is in flight during + the non-I2C mux-changing operation. ==== ===================================================================== @@ -137,14 +137,14 @@ Mux-locked Example When there is an access to D1, this happens: - 1. Someone issues an i2c-transfer to D1. + 1. Someone issues an I2C transfer to D1. 2. M1 locks muxes on its parent (the root adapter in this case). 3. M1 calls ->select to ready the mux. - 4. M1 (presumably) does some i2c-transfers as part of its select. - These transfers are normal i2c-transfers that locks the parent + 4. M1 (presumably) does some I2C transfers as part of its select. + These transfers are normal I2C transfers that locks the parent adapter. - 5. M1 feeds the i2c-transfer from step 1 to its parent adapter as a - normal i2c-transfer that locks the parent adapter. + 5. M1 feeds the I2C transfer from step 1 to its parent adapter as a + normal I2C transfer that locks the parent adapter. 6. M1 calls ->deselect, if it has one. 7. Same rules as in step 4, but for ->deselect. 8. M1 unlocks muxes on its parent. @@ -159,8 +159,8 @@ Parent-locked muxes Parent-locked muxes lock the parent adapter during the full select- transfer-deselect transaction. The implication is that the mux driver -has to ensure that any and all i2c transfers through that parent -adapter during the transaction are unlocked i2c transfers (using e.g. +has to ensure that any and all I2C transfers through that parent +adapter during the transaction are unlocked I2C transfers (using e.g. __i2c_transfer), or a deadlock will follow. There are a couple of caveats. @@ -169,12 +169,12 @@ PL1. If you build a topology with a parent-locked mux being the child of another mux, this might break a possible assumption from the child mux that the root adapter is unused between its select op and the actual transfer (e.g. if the child mux is auto-closing - and the parent mux issus i2c-transfers as part of its select). + and the parent mux issues I2C transfers as part of its select). This is especially the case if the parent mux is mux-locked, but it may also happen if the parent mux is parent-locked. PL2. If select/deselect calls out to other subsystems such as gpio, - pinctrl, regmap or iio, it is essential that any i2c transfers + pinctrl, regmap or iio, it is essential that any I2C transfers caused by these subsystems are unlocked. This can be convoluted to accomplish, maybe even impossible if an acceptably clean solution is sought. @@ -197,15 +197,15 @@ Parent-locked Example When there is an access to D1, this happens: - 1. Someone issues an i2c-transfer to D1. + 1. Someone issues an I2C transfer to D1. 2. M1 locks muxes on its parent (the root adapter in this case). 3. M1 locks its parent adapter. 4. M1 calls ->select to ready the mux. - 5. If M1 does any i2c-transfers (on this root adapter) as part of - its select, those transfers must be unlocked i2c-transfers so + 5. If M1 does any I2C transfers (on this root adapter) as part of + its select, those transfers must be unlocked I2C transfers so that they do not deadlock the root adapter. - 6. M1 feeds the i2c-transfer from step 1 to the root adapter as an - unlocked i2c-transfer, so that it does not deadlock the parent + 6. M1 feeds the I2C transfer from step 1 to the root adapter as an + unlocked I2C transfer, so that it does not deadlock the parent adapter. 7. M1 calls ->deselect, if it has one. 8. Same rules as in step 5, but for ->deselect. @@ -240,7 +240,7 @@ and specifically when M2 requests its parent to lock, M1 passes the buck to the root adapter). This topology is bad if M2 is an auto-closing mux and M1->select -issues any unlocked i2c transfers on the root adapter that may leak +issues any unlocked I2C transfers on the root adapter that may leak through and be seen by the M2 adapter, thus closing M2 prematurely. @@ -286,14 +286,14 @@ point. This kind of topology is generally not suitable and should probably be avoided. The reason is that M2 probably assumes that there will -be no i2c transfers during its calls to ->select and ->deselect, and +be no I2C transfers during its calls to ->select and ->deselect, and if there are, any such transfers might appear on the slave side of M2 -as partial i2c transfers, i.e. garbage or worse. This might cause +as partial I2C transfers, i.e. garbage or worse. This might cause device lockups and/or other problems. The topology is especially troublesome if M2 is an auto-closing mux. In that case, any interleaved accesses to D4 might close M2 -prematurely, as might any i2c-transfers part of M1->select. +prematurely, as might any I2C transfers part of M1->select. 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busses/index + i2c-topology + muxes/i2c-mux-gpio + +Writing device drivers +====================== + +.. toctree:: + :maxdepth: 1 + + writing-clients dev-interface dma-considerations fault-codes functionality + +Debugging +========= + +.. toctree:: + :maxdepth: 1 + gpio-fault-injection - i2c-protocol i2c-stub - i2c-topology - instantiating-devices - old-module-parameters - slave-eeprom-backend + +Slave I2C +========= + +.. toctree:: + :maxdepth: 1 + slave-interface - smbus-protocol - summary + slave-eeprom-backend + +Advanced topics +=============== + +.. toctree:: + :maxdepth: 1 + ten-bit-addresses - upgrading-clients - writing-clients - muxes/i2c-mux-gpio +Legacy documentation +==================== - busses/index +.. toctree:: + :maxdepth: 1 + + upgrading-clients + old-module-parameters .. only:: subproject and html diff --git a/Documentation/i2c/instantiating-devices.rst b/Documentation/i2c/instantiating-devices.rst index 875ebe9e78e3..e558e0a77e0c 100644 --- a/Documentation/i2c/instantiating-devices.rst +++ b/Documentation/i2c/instantiating-devices.rst @@ -9,54 +9,27 @@ reason, the kernel code must instantiate I2C devices explicitly. There are several ways to achieve this, depending on the context and requirements. -Method 1a: Declare the I2C devices by bus number ------------------------------------------------- +Method 1: Declare the I2C devices statically +-------------------------------------------- This method is appropriate when the I2C bus is a system bus as is the case -for many embedded systems. On such systems, each I2C bus has a number -which is known in advance. It is thus possible to pre-declare the I2C -devices which live on this bus. This is done with an array of struct -i2c_board_info which is registered by calling i2c_register_board_info(). +for many embedded systems. On such systems, each I2C bus has a number which +is known in advance. It is thus possible to pre-declare the I2C devices +which live on this bus. -Example (from omap2 h4):: +This information is provided to the kernel in a different way on different +architectures: device tree, ACPI or board files. - static struct i2c_board_info h4_i2c_board_info[] __initdata = { - { - I2C_BOARD_INFO("isp1301_omap", 0x2d), - .irq = OMAP_GPIO_IRQ(125), - }, - { /* EEPROM on mainboard */ - I2C_BOARD_INFO("24c01", 0x52), - .platform_data = &m24c01, - }, - { /* EEPROM on cpu card */ - I2C_BOARD_INFO("24c01", 0x57), - .platform_data = &m24c01, - }, - }; - - static void __init omap_h4_init(void) - { - (...) - i2c_register_board_info(1, h4_i2c_board_info, - ARRAY_SIZE(h4_i2c_board_info)); - (...) - } - -The above code declares 3 devices on I2C bus 1, including their respective -addresses and custom data needed by their drivers. When the I2C bus in -question is registered, the I2C devices will be instantiated automatically -by i2c-core. +When the I2C bus in question is registered, the I2C devices will be +instantiated automatically by i2c-core. The devices will be automatically +unbound and destroyed when the I2C bus they sit on goes away (if ever). -The devices will be automatically unbound and destroyed when the I2C bus -they sit on goes away (if ever.) +Declare the I2C devices via devicetree +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ -Method 1b: Declare the I2C devices via devicetree -------------------------------------------------- - -This method has the same implications as method 1a. The declaration of I2C -devices is here done via devicetree as subnodes of the master controller. +On platforms using devicetree, the declaration of I2C devices is done in +subnodes of the master controller. Example:: @@ -82,11 +55,49 @@ additional properties which might be needed to set up the device, please refer to its devicetree documentation in Documentation/devicetree/bindings/. -Method 1c: Declare the I2C devices via ACPI -------------------------------------------- +Declare the I2C devices via ACPI +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ACPI can also describe I2C devices. There is special documentation for this -which is currently located at Documentation/firmware-guide/acpi/enumeration.rst. +which is currently located at :doc:`../firmware-guide/acpi/enumeration`. + + +Declare the I2C devices in board files +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +In many embedded architectures, devicetree has replaced the old hardware +description based on board files, but the latter are still used in old +code. Instantiating I2C devices via board files is done with an array of +struct i2c_board_info which is registered by calling +i2c_register_board_info(). + +Example (from omap2 h4):: + + static struct i2c_board_info h4_i2c_board_info[] __initdata = { + { + I2C_BOARD_INFO("isp1301_omap", 0x2d), + .irq = OMAP_GPIO_IRQ(125), + }, + { /* EEPROM on mainboard */ + I2C_BOARD_INFO("24c01", 0x52), + .platform_data = &m24c01, + }, + { /* EEPROM on cpu card */ + I2C_BOARD_INFO("24c01", 0x57), + .platform_data = &m24c01, + }, + }; + + static void __init omap_h4_init(void) + { + (...) + i2c_register_board_info(1, h4_i2c_board_info, + ARRAY_SIZE(h4_i2c_board_info)); + (...) + } + +The above code declares 3 devices on I2C bus 1, including their respective +addresses and custom data needed by their drivers. Method 2: Instantiate the devices explicitly @@ -98,7 +109,7 @@ tuner, a video decoder, an audio decoder, etc. usually connected to the main chip by the means of an I2C bus. You won't know the number of the I2C bus in advance, so the method 1 described above can't be used. Instead, you can instantiate your I2C devices explicitly. This is done by filling -a struct i2c_board_info and calling i2c_new_device(). +a struct i2c_board_info and calling i2c_new_client_device(). Example (from the sfe4001 network driver):: @@ -110,7 +121,7 @@ Example (from the sfe4001 network driver):: { (...) efx->board_info.hwmon_client = - i2c_new_device(&efx->i2c_adap, &sfe4001_hwmon_info); + i2c_new_client_device(&efx->i2c_adap, &sfe4001_hwmon_info); (...) } @@ -123,7 +134,7 @@ present or not (for example for an optional feature which is not present on cheap variants of a board but you have no way to tell them apart), or it may have different addresses from one board to the next (manufacturer changing its design without notice). In this case, you can call -i2c_new_scanned_device() instead of i2c_new_device(). +i2c_new_scanned_device() instead of i2c_new_client_device(). Example (from the nxp OHCI driver):: @@ -152,7 +163,7 @@ simply gives up. The driver which instantiated the I2C device is responsible for destroying it on cleanup. This is done by calling i2c_unregister_device() on the -pointer that was earlier returned by i2c_new_device() or +pointer that was earlier returned by i2c_new_client_device() or i2c_new_scanned_device(). @@ -188,7 +199,7 @@ destroyed automatically when the driver which detected them is removed, or when the underlying I2C bus is itself destroyed, whichever happens first. -Those of you familiar with the i2c subsystem of 2.4 kernels and early 2.6 +Those of you familiar with the I2C subsystem of 2.4 kernels and early 2.6 kernels will find out that this method 3 is essentially similar to what was done there. Two significant differences are: @@ -214,15 +225,15 @@ In general, the kernel should know which I2C devices are connected and what addresses they live at. However, in certain cases, it does not, so a sysfs interface was added to let the user provide the information. This interface is made of 2 attribute files which are created in every I2C bus -directory: new_device and delete_device. Both files are write only and you -must write the right parameters to them in order to properly instantiate, -respectively delete, an I2C device. +directory: ``new_device`` and ``delete_device``. Both files are write +only and you must write the right parameters to them in order to properly +instantiate, respectively delete, an I2C device. -File new_device takes 2 parameters: the name of the I2C device (a string) -and the address of the I2C device (a number, typically expressed in -hexadecimal starting with 0x, but can also be expressed in decimal.) +File ``new_device`` takes 2 parameters: the name of the I2C device (a +string) and the address of the I2C device (a number, typically expressed +in hexadecimal starting with 0x, but can also be expressed in decimal.) -File delete_device takes a single parameter: the address of the I2C +File ``delete_device`` takes a single parameter: the address of the I2C device. As no two devices can live at the same address on a given I2C segment, the address is sufficient to uniquely identify the device to be deleted. diff --git a/Documentation/i2c/old-module-parameters.rst b/Documentation/i2c/old-module-parameters.rst index a1939512ad66..38e55829dee8 100644 --- a/Documentation/i2c/old-module-parameters.rst +++ b/Documentation/i2c/old-module-parameters.rst @@ -1,19 +1,24 @@ -================================================= -I2C device driver binding control from user-space -================================================= +================================================================ +I2C device driver binding control from user-space in old kernels +================================================================ -Up to kernel 2.6.32, many i2c drivers used helper macros provided by +.. NOTE:: + Note: this section is only relevant if you are handling some old code + found in kernel 2.6. If you work with more recent kernels, you can + safely skip this section. + +Up to kernel 2.6.32, many I2C drivers used helper macros provided by <linux/i2c.h> which created standard module parameters to let the user -control how the driver would probe i2c buses and attach to devices. These -parameters were known as "probe" (to let the driver probe for an extra -address), "force" (to forcibly attach the driver to a given device) and -"ignore" (to prevent a driver from probing a given address). +control how the driver would probe I2C buses and attach to devices. These +parameters were known as ``probe`` (to let the driver probe for an extra +address), ``force`` (to forcibly attach the driver to a given device) and +``ignore`` (to prevent a driver from probing a given address). -With the conversion of the i2c subsystem to the standard device driver +With the conversion of the I2C subsystem to the standard device driver binding model, it became clear that these per-module parameters were no longer needed, and that a centralized implementation was possible. The new, -sysfs-based interface is described in the documentation file -"instantiating-devices", section "Method 4: Instantiate from user-space". +sysfs-based interface is described in :doc:`instantiating-devices`, section +"Method 4: Instantiate from user-space". Below is a mapping from the old module parameters to the new interface. @@ -42,8 +47,8 @@ New method (sysfs interface):: # echo dummy 0x2f > /sys/bus/i2c/devices/i2c-1/new_device # modprobe <driver> -Of course, it is important to instantiate the "dummy" device before loading +Of course, it is important to instantiate the ``dummy`` device before loading the driver. The dummy device will be handled by i2c-core itself, preventing other drivers from binding to it later on. If there is a real device at the problematic address, and you want another driver to bind to it, then simply -pass the name of the device in question instead of "dummy". +pass the name of the device in question instead of ``dummy``. diff --git a/Documentation/i2c/slave-interface.rst b/Documentation/i2c/slave-interface.rst index c769bd6a15bf..82ea3e1d6fe4 100644 --- a/Documentation/i2c/slave-interface.rst +++ b/Documentation/i2c/slave-interface.rst @@ -59,7 +59,7 @@ The bus driver sends an event to the backend using the following function:: ret = i2c_slave_event(client, event, &val) -'client' describes the i2c slave device. 'event' is one of the special event +'client' describes the I2C slave device. 'event' is one of the special event types described hereafter. 'val' holds an u8 value for the data byte to be read/written and is thus bidirectional. The pointer to val must always be provided even if val is not used for an event, i.e. don't use NULL here. 'ret' @@ -143,7 +143,7 @@ Bus driver support If you want to add slave support to the bus driver: * implement calls to register/unregister the slave and add those to the - struct i2c_algorithm. When registering, you probably need to set the i2c + struct i2c_algorithm. When registering, you probably need to set the I2C slave address and enable slave specific interrupts. If you use runtime pm, you should use pm_runtime_get_sync() because your device usually needs to be powered on always to be able to detect its slave address. When unregistering, diff --git a/Documentation/i2c/smbus-protocol.rst b/Documentation/i2c/smbus-protocol.rst index e30eb1d274c6..c122ed239f7f 100644 --- a/Documentation/i2c/smbus-protocol.rst +++ b/Documentation/i2c/smbus-protocol.rst @@ -1,6 +1,6 @@ -====================== -SMBus Protocol Summary -====================== +================== +The SMBus Protocol +================== The following is a summary of the SMBus protocol. It applies to all revisions of the protocol (1.0, 1.1, and 2.0). @@ -27,27 +27,27 @@ a different protocol operation entirely. Each transaction type corresponds to a functionality flag. Before calling a transaction function, a device driver should always check (just once) for the corresponding functionality flag to ensure that the underlying I2C -adapter supports the transaction in question. See -<file:Documentation/i2c/functionality.rst> for the details. +adapter supports the transaction in question. See :doc:`functionality` for +the details. Key to symbols ============== =============== ============================================================= -S (1 bit) : Start bit -P (1 bit) : Stop bit -Rd/Wr (1 bit) : Read/Write bit. Rd equals 1, Wr equals 0. -A, NA (1 bit) : Accept and reverse accept bit. -Addr (7 bits): I2C 7 bit address. Note that this can be expanded as usual to +S Start condition +P Stop condition +Rd/Wr (1 bit) Read/Write bit. Rd equals 1, Wr equals 0. +A, NA (1 bit) Acknowledge (ACK) and Not Acknowledge (NACK) bit +Addr (7 bits) I2C 7 bit address. Note that this can be expanded as usual to get a 10 bit I2C address. -Comm (8 bits): Command byte, a data byte which often selects a register on +Comm (8 bits) Command byte, a data byte which often selects a register on the device. -Data (8 bits): A plain data byte. Sometimes, I write DataLow, DataHigh +Data (8 bits) A plain data byte. Sometimes, I write DataLow, DataHigh for 16 bit data. -Count (8 bits): A data byte containing the length of a block operation. +Count (8 bits) A data byte containing the length of a block operation. -[..]: Data sent by I2C device, as opposed to data sent by the host +[..] Data sent by I2C device, as opposed to data sent by the host adapter. =============== ============================================================= @@ -62,8 +62,10 @@ This sends a single bit to the device, at the place of the Rd/Wr bit:: Functionality flag: I2C_FUNC_SMBUS_QUICK -SMBus Receive Byte: i2c_smbus_read_byte() -========================================== +SMBus Receive Byte +================== + +Implemented by i2c_smbus_read_byte() This reads a single byte from a device, without specifying a device register. Some devices are so simple that this interface is enough; for @@ -75,8 +77,10 @@ the previous SMBus command:: Functionality flag: I2C_FUNC_SMBUS_READ_BYTE -SMBus Send Byte: i2c_smbus_write_byte() -======================================== +SMBus Send Byte +=============== + +Implemented by i2c_smbus_write_byte() This operation is the reverse of Receive Byte: it sends a single byte to a device. See Receive Byte for more information. @@ -88,8 +92,10 @@ to a device. See Receive Byte for more information. Functionality flag: I2C_FUNC_SMBUS_WRITE_BYTE -SMBus Read Byte: i2c_smbus_read_byte_data() -============================================ +SMBus Read Byte +=============== + +Implemented by i2c_smbus_read_byte_data() This reads a single byte from a device, from a designated register. The register is specified through the Comm byte:: @@ -99,8 +105,10 @@ The register is specified through the Comm byte:: Functionality flag: I2C_FUNC_SMBUS_READ_BYTE_DATA -SMBus Read Word: i2c_smbus_read_word_data() -============================================ +SMBus Read Word +=============== + +Implemented by i2c_smbus_read_word_data() This operation is very like Read Byte; again, data is read from a device, from a designated register that is specified through the Comm @@ -110,13 +118,15 @@ byte. But this time, the data is a complete word (16 bits):: Functionality flag: I2C_FUNC_SMBUS_READ_WORD_DATA -Note the convenience function i2c_smbus_read_word_swapped is +Note the convenience function i2c_smbus_read_word_swapped() is available for reads where the two data bytes are the other way around (not SMBus compliant, but very popular.) -SMBus Write Byte: i2c_smbus_write_byte_data() -============================================== +SMBus Write Byte +================ + +Implemented by i2c_smbus_write_byte_data() This writes a single byte to a device, to a designated register. The register is specified through the Comm byte. This is the opposite of @@ -129,24 +139,26 @@ the Read Byte operation. Functionality flag: I2C_FUNC_SMBUS_WRITE_BYTE_DATA -SMBus Write Word: i2c_smbus_write_word_data() -============================================== +SMBus Write Word +================ + +Implemented by i2c_smbus_write_word_data() This is the opposite of the Read Word operation. 16 bits -of data is written to a device, to the designated register that is -specified through the Comm byte.:: +of data are written to a device, to the designated register that is +specified through the Comm byte:: S Addr Wr [A] Comm [A] DataLow [A] DataHigh [A] P Functionality flag: I2C_FUNC_SMBUS_WRITE_WORD_DATA -Note the convenience function i2c_smbus_write_word_swapped is +Note the convenience function i2c_smbus_write_word_swapped() is available for writes where the two data bytes are the other way around (not SMBus compliant, but very popular.) -SMBus Process Call: -=================== +SMBus Process Call +================== This command selects a device register (through the Comm byte), sends 16 bits of data to it, and reads 16 bits of data in return:: @@ -157,8 +169,10 @@ This command selects a device register (through the Comm byte), sends Functionality flag: I2C_FUNC_SMBUS_PROC_CALL -SMBus Block Read: i2c_smbus_read_block_data() -============================================== +SMBus Block Read +================ + +Implemented by i2c_smbus_read_block_data() This command reads a block of up to 32 bytes from a device, from a designated register that is specified through the Comm byte. The amount @@ -172,8 +186,10 @@ of data is specified by the device in the Count byte. Functionality flag: I2C_FUNC_SMBUS_READ_BLOCK_DATA -SMBus Block Write: i2c_smbus_write_block_data() -================================================ +SMBus Block Write +================= + +Implemented by i2c_smbus_write_block_data() The opposite of the Block Read command, this writes up to 32 bytes to a device, to a designated register that is specified through the @@ -266,16 +282,19 @@ This is implemented the following way in the Linux kernel: I2C Block Transactions ====================== -The following I2C block transactions are supported by the -SMBus layer and are described here for completeness. -They are *NOT* defined by the SMBus specification. +The following I2C block transactions are similar to the SMBus Block Read +and Write operations, except these do not have a Count byte. They are +supported by the SMBus layer and are described here for completeness, but +they are *NOT* defined by the SMBus specification. I2C block transactions do not limit the number of bytes transferred but the SMBus layer places a limit of 32 bytes. -I2C Block Read: i2c_smbus_read_i2c_block_data() -================================================ +I2C Block Read +============== + +Implemented by i2c_smbus_read_i2c_block_data() This command reads a block of bytes from a device, from a designated register that is specified through the Comm byte:: @@ -286,8 +305,10 @@ designated register that is specified through the Comm byte:: Functionality flag: I2C_FUNC_SMBUS_READ_I2C_BLOCK -I2C Block Write: i2c_smbus_write_i2c_block_data() -================================================== +I2C Block Write +=============== + +Implemented by i2c_smbus_write_i2c_block_data() The opposite of the Block Read command, this writes bytes to a device, to a designated register that is specified through the diff --git a/Documentation/i2c/summary.rst b/Documentation/i2c/summary.rst index 3a24eac17375..ce7230025b33 100644 --- a/Documentation/i2c/summary.rst +++ b/Documentation/i2c/summary.rst @@ -1,13 +1,19 @@ -============= -I2C and SMBus -============= - -I2C (pronounce: I squared C) is a protocol developed by Philips. It is a -slow two-wire protocol (variable speed, up to 400 kHz), with a high speed -extension (3.4 MHz). It provides an inexpensive bus for connecting many -types of devices with infrequent or low bandwidth communications needs. -I2C is widely used with embedded systems. Some systems use variants that -don't meet branding requirements, and so are not advertised as being I2C. +============================= +Introduction to I2C and SMBus +============================= + +I²C (pronounce: I squared C and written I2C in the kernel documentation) is +a protocol developed by Philips. It is a slow two-wire protocol (variable +speed, up to 400 kHz), with a high speed extension (3.4 MHz). It provides +an inexpensive bus for connecting many types of devices with infrequent or +low bandwidth communications needs. I2C is widely used with embedded +systems. Some systems use variants that don't meet branding requirements, +and so are not advertised as being I2C but come under different names, +e.g. TWI (Two Wire Interface), IIC. + +The official I2C specification is the `"I2C-bus specification and user +manual" (UM10204) <https://www.nxp.com/docs/en/user-guide/UM10204.pdf>`_ +published by NXP Semiconductors. SMBus (System Management Bus) is based on the I2C protocol, and is mostly a subset of I2C protocols and signaling. Many I2C devices will work on an @@ -25,21 +31,29 @@ implement all the common SMBus protocol semantics or messages. Terminology =========== -When we talk about I2C, we use the following terms:: +Using the terminology from the official documentation, the I2C bus connects +one or more *master* chips and one or more *slave* chips. + +.. kernel-figure:: i2c.svg + :alt: Simple I2C bus with one master and 3 slaves + + Simple I2C bus - Bus -> Algorithm - Adapter - Device -> Driver - Client +A **master** chip is a node that starts communications with slaves. In the +Linux kernel implementation it is called an **adapter** or bus. Adapter +drivers are in the ``drivers/i2c/busses/`` subdirectory. -An Algorithm driver contains general code that can be used for a whole class -of I2C adapters. Each specific adapter driver either depends on one algorithm -driver, or includes its own implementation. +An **algorithm** contains general code that can be used to implement a +whole class of I2C adapters. Each specific adapter driver either depends on +an algorithm driver in the ``drivers/i2c/algos/`` subdirectory, or includes +its own implementation. -A Driver driver (yes, this sounds ridiculous, sorry) contains the general -code to access some type of device. Each detected device gets its own -data in the Client structure. Usually, Driver and Client are more closely -integrated than Algorithm and Adapter. +A **slave** chip is a node that responds to communications when addressed +by the master. In Linux it is called a **client**. Client drivers are kept +in a directory specific to the feature they provide, for example +``drivers/media/gpio/`` for GPIO expanders and ``drivers/media/i2c/`` for +video-related chips. -For a given configuration, you will need a driver for your I2C bus, and -drivers for your I2C devices (usually one driver for each device). +For the example configuration in figure, you will need a driver for your +I2C adapter, and drivers for your I2C devices (usually one driver for each +device). diff --git a/Documentation/i2c/writing-clients.rst b/Documentation/i2c/writing-clients.rst index ced309b5e0cc..978cc8210bf3 100644 --- a/Documentation/i2c/writing-clients.rst +++ b/Documentation/i2c/writing-clients.rst @@ -1,6 +1,6 @@ -=================== -Writing I2C Clients -=================== +=============================== +Implementing I2C device drivers +=============================== This is a small guide for those who want to write kernel drivers for I2C or SMBus devices, using Linux as the protocol host/master (not slave). @@ -95,7 +95,7 @@ to gather information from the client, or write new information to the client. I have found it useful to define foo_read and foo_write functions for this. -For some cases, it will be easier to call the i2c functions directly, +For some cases, it will be easier to call the I2C functions directly, but many chips have some kind of register-value idea that can easily be encapsulated. @@ -175,8 +175,8 @@ Device Creation If you know for a fact that an I2C device is connected to a given I2C bus, you can instantiate that device by simply filling an i2c_board_info structure with the device address and driver name, and calling -i2c_new_device(). This will create the device, then the driver core will -take care of finding the right driver and will call its probe() method. +i2c_new_client_device(). This will create the device, then the driver core +will take care of finding the right driver and will call its probe() method. If a driver supports different device types, you can specify the type you want using the type field. You can also specify an IRQ and platform data if needed. @@ -186,14 +186,14 @@ don't know the exact address it uses. This happens on TV adapters for example, where the same driver supports dozens of slightly different models, and I2C device addresses change from one model to the next. In that case, you can use the i2c_new_scanned_device() variant, which is -similar to i2c_new_device(), except that it takes an additional list of -possible I2C addresses to probe. A device is created for the first +similar to i2c_new_client_device(), except that it takes an additional list +of possible I2C addresses to probe. A device is created for the first responsive address in the list. If you expect more than one device to be present in the address range, simply call i2c_new_scanned_device() that many times. -The call to i2c_new_device() or i2c_new_scanned_device() typically happens -in the I2C bus driver. You may want to save the returned i2c_client +The call to i2c_new_client_device() or i2c_new_scanned_device() typically +happens in the I2C bus driver. You may want to save the returned i2c_client reference for later use. @@ -236,11 +236,11 @@ possible. Device Deletion --------------- -Each I2C device which has been created using i2c_new_device() or -i2c_new_scanned_device() can be unregistered by calling +Each I2C device which has been created using i2c_new_client_device() +or i2c_new_scanned_device() can be unregistered by calling i2c_unregister_device(). If you don't call it explicitly, it will be -called automatically before the underlying I2C bus itself is removed, as a -device can't survive its parent in the device driver model. +called automatically before the underlying I2C bus itself is removed, +as a device can't survive its parent in the device driver model. Initializing the driver @@ -344,7 +344,7 @@ Plain I2C communication int i2c_master_recv(struct i2c_client *client, char *buf, int count); These routines read and write some bytes from/to a client. The client -contains the i2c address, so you do not have to include it. The second +contains the I2C address, so you do not have to include it. The second parameter contains the bytes to read/write, the third the number of bytes to read/write (must be less than the length of the buffer, also should be less than 64k since msg.len is u16.) Returned is the actual number of bytes @@ -357,9 +357,9 @@ read/written. This sends a series of messages. Each message can be a read or write, and they can be mixed in any way. The transactions are combined: no -stop bit is sent between transaction. The i2c_msg structure contains -for each message the client address, the number of bytes of the message -and the message data itself. +stop condition is issued between transaction. The i2c_msg structure +contains for each message the client address, the number of bytes of the +message and the message data itself. You can read the file ``i2c-protocol`` for more information about the actual I2C protocol. |
