diff options
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/devicetree/bindings/i2c/i2c-davinci.txt | 3 | ||||
| -rw-r--r-- | Documentation/devicetree/bindings/i2c/i2c-digicolor.txt | 25 | ||||
| -rw-r--r-- | Documentation/devicetree/bindings/i2c/i2c-jz4780.txt | 35 | ||||
| -rw-r--r-- | Documentation/devicetree/bindings/i2c/i2c-xlp9xx.txt | 22 | ||||
| -rw-r--r-- | Documentation/devicetree/bindings/vendor-prefixes.txt | 1 | ||||
| -rw-r--r-- | Documentation/i2c/slave-eeprom-backend | 14 | ||||
| -rw-r--r-- | Documentation/i2c/slave-interface | 179 | ||||
| -rw-r--r-- | Documentation/i2c/summary | 4 |
8 files changed, 279 insertions, 4 deletions
diff --git a/Documentation/devicetree/bindings/i2c/i2c-davinci.txt b/Documentation/devicetree/bindings/i2c/i2c-davinci.txt index 2dc935b4113d..a4e1cbc810c1 100644 --- a/Documentation/devicetree/bindings/i2c/i2c-davinci.txt +++ b/Documentation/devicetree/bindings/i2c/i2c-davinci.txt @@ -10,6 +10,9 @@ Required properties: Recommended properties : - interrupts : standard interrupt property. - clock-frequency : desired I2C bus clock frequency in Hz. +- ti,has-pfunc: boolean; if defined, it indicates that SoC supports PFUNC + registers. PFUNC registers allow to switch I2C pins to function as + GPIOs, so they can by toggled manually. Example (enbw_cmc board): i2c@1c22000 { diff --git a/Documentation/devicetree/bindings/i2c/i2c-digicolor.txt b/Documentation/devicetree/bindings/i2c/i2c-digicolor.txt new file mode 100644 index 000000000000..457a098d4f7e --- /dev/null +++ b/Documentation/devicetree/bindings/i2c/i2c-digicolor.txt @@ -0,0 +1,25 @@ +Conexant Digicolor I2C controller + +Required properties: + - compatible: must be "cnxt,cx92755-i2c" + - reg: physical address and length of the device registers + - interrupts: a single interrupt specifier + - clocks: clock for the device + - #address-cells: should be <1> + - #size-cells: should be <0> + +Optional properties: +- clock-frequency: the desired I2C bus clock frequency in Hz; in + absence of this property the default value is used (100 kHz). + +Example: + + i2c: i2c@f0000120 { + compatible = "cnxt,cx92755-i2c"; + reg = <0xf0000120 0x10>; + interrupts = <28>; + clocks = <&main_clk>; + clock-frequency = <100000>; + #address-cells = <1>; + #size-cells = <0>; + }; diff --git a/Documentation/devicetree/bindings/i2c/i2c-jz4780.txt b/Documentation/devicetree/bindings/i2c/i2c-jz4780.txt new file mode 100644 index 000000000000..231e4cc4008c --- /dev/null +++ b/Documentation/devicetree/bindings/i2c/i2c-jz4780.txt @@ -0,0 +1,35 @@ +* Ingenic JZ4780 I2C Bus controller + +Required properties: +- compatible: should be "ingenic,jz4780-i2c" +- reg: Should contain the address & size of the I2C controller registers. +- interrupts: Should specify the interrupt provided by parent. +- clocks: Should contain a single clock specifier for the JZ4780 I2C clock. +- clock-frequency: desired I2C bus clock frequency in Hz. + +Recommended properties: +- pinctrl-names: should be "default"; +- pinctrl-0: phandle to pinctrl function + +Optional properties: +- interrupt-parent: Should be the phandle of the interrupt controller that + delivers interrupts to the I2C block. + +Example + +/ { + i2c4: i2c4@0x10054000 { + compatible = "ingenic,jz4780-i2c"; + reg = <0x10054000 0x1000>; + + interrupt-parent = <&intc>; + interrupts = <56>; + + clocks = <&cgu JZ4780_CLK_SMB4>; + clock-frequency = <100000>; + pinctrl-names = "default"; + pinctrl-0 = <&pins_i2c4_data>; + + }; +}; + diff --git a/Documentation/devicetree/bindings/i2c/i2c-xlp9xx.txt b/Documentation/devicetree/bindings/i2c/i2c-xlp9xx.txt new file mode 100644 index 000000000000..f818ef507ab7 --- /dev/null +++ b/Documentation/devicetree/bindings/i2c/i2c-xlp9xx.txt @@ -0,0 +1,22 @@ +Device tree configuration for the I2C controller on the XLP9xx/5xx SoC + +Required properties: +- compatible : should be "netlogic,xlp980-i2c" +- reg : bus address start and address range size of device +- interrupts : interrupt number + +Optional properties: +- clock-frequency : frequency of bus clock in Hz + Defaults to 100 KHz when the property is not specified + +Example: + +i2c0: i2c@113100 { + compatible = "netlogic,xlp980-i2c"; + #address-cells = <1>; + #size-cells = <0>; + reg = <0 0x113100 0x100>; + clock-frequency = <400000>; + interrupts = <30>; + interrupt-parent = <&pic>; +}; diff --git a/Documentation/devicetree/bindings/vendor-prefixes.txt b/Documentation/devicetree/bindings/vendor-prefixes.txt index 9b98bd89cfe2..8764b5b78772 100644 --- a/Documentation/devicetree/bindings/vendor-prefixes.txt +++ b/Documentation/devicetree/bindings/vendor-prefixes.txt @@ -125,6 +125,7 @@ mxicy Macronix International Co., Ltd. national National Semiconductor neonode Neonode Inc. netgear NETGEAR +netlogic Broadcom Corporation (formerly NetLogic Microsystems) newhaven Newhaven Display International nintendo Nintendo nokia Nokia diff --git a/Documentation/i2c/slave-eeprom-backend b/Documentation/i2c/slave-eeprom-backend new file mode 100644 index 000000000000..c8444ef82acf --- /dev/null +++ b/Documentation/i2c/slave-eeprom-backend @@ -0,0 +1,14 @@ +Linux I2C slave eeprom backend +============================== + +by Wolfram Sang <wsa@sang-engineering.com> in 2014-15 + +This is a proof-of-concept backend which acts like an EEPROM on the connected +I2C bus. The memory contents can be modified from userspace via this file +located in sysfs: + + /sys/bus/i2c/devices/<device-direcory>/slave-eeprom + +As of 2015, Linux doesn't support poll on binary sysfs files, so there is no +notfication when another master changed the content. + diff --git a/Documentation/i2c/slave-interface b/Documentation/i2c/slave-interface new file mode 100644 index 000000000000..389bb5d61854 --- /dev/null +++ b/Documentation/i2c/slave-interface @@ -0,0 +1,179 @@ +Linux I2C slave interface description +===================================== + +by Wolfram Sang <wsa@sang-engineering.com> in 2014-15 + +Linux can also be an I2C slave in case I2C controllers have slave support. +Besides this HW requirement, one also needs a software backend providing the +actual functionality. An example for this is the slave-eeprom driver, which +acts as a dual memory driver. While another I2C master on the bus can access it +like a regular EEPROM, the Linux I2C slave can access the content via sysfs and +retrieve/provide information as needed. The software backend driver and the I2C +bus driver communicate via events. Here is a small graph visualizing the data +flow and the means by which data is transported. The dotted line marks only one +example. The backend could also use e.g. a character device, be in-kernel +only, or something completely different: + + + e.g. sysfs I2C slave events I/O registers + +-----------+ v +---------+ v +--------+ v +------------+ + | Userspace +........+ Backend +-----------+ Driver +-----+ Controller | + +-----------+ +---------+ +--------+ +------------+ + | | + ----------------------------------------------------------------+-- I2C + --------------------------------------------------------------+---- Bus + +Note: Technically, there is also the I2C core between the backend and the +driver. However, at this time of writing, the layer is transparent. + + +User manual +=========== + +I2C slave backends behave like standard I2C clients. So, you can instantiate +them like described in the document 'instantiating-devices'. A quick example +for instantiating the slave-eeprom driver from userspace: + + # echo 0-0064 > /sys/bus/i2c/drivers/i2c-slave-eeprom/bind + +Each backend should come with separate documentation to describe its specific +behaviour and setup. + + +Developer manual +================ + +I2C slave events +---------------- + +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 +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' +is the return value from the backend. Mandatory events must be provided by the +bus drivers and must be checked for by backend drivers. + +Event types: + +* I2C_SLAVE_WRITE_REQUESTED (mandatory) + +'val': unused +'ret': always 0 + +Another I2C master wants to write data to us. This event should be sent once +our own address and the write bit was detected. The data did not arrive yet, so +there is nothing to process or return. Wakeup or initialization probably needs +to be done, though. + +* I2C_SLAVE_READ_REQUESTED (mandatory) + +'val': backend returns first byte to be sent +'ret': always 0 + +Another I2C master wants to read data from us. This event should be sent once +our own address and the read bit was detected. After returning, the bus driver +should transmit the first byte. + +* I2C_SLAVE_WRITE_RECEIVED (mandatory) + +'val': bus driver delivers received byte +'ret': 0 if the byte should be acked, some errno if the byte should be nacked + +Another I2C master has sent a byte to us which needs to be set in 'val'. If 'ret' +is zero, the bus driver should ack this byte. If 'ret' is an errno, then the byte +should be nacked. + +* I2C_SLAVE_READ_PROCESSED (mandatory) + +'val': backend returns next byte to be sent +'ret': always 0 + +The bus driver requests the next byte to be sent to another I2C master in +'val'. Important: This does not mean that the previous byte has been acked, it +only means that the previous byte is shifted out to the bus! To ensure seamless +transmission, most hardware requests the next byte when the previous one is +still shifted out. If the master sends NACK and stops reading after the byte +currently shifted out, this byte requested here is never used. It very likely +needs to be sent again on the next I2C_SLAVE_READ_REQUEST, depending a bit on +your backend, though. + +* I2C_SLAVE_STOP (mandatory) + +'val': unused +'ret': always 0 + +A stop condition was received. This can happen anytime and the backend should +reset its state machine for I2C transfers to be able to receive new requests. + + +Software backends +----------------- + +If you want to write a software backend: + +* use a standard i2c_driver and its matching mechanisms +* write the slave_callback which handles the above slave events + (best using a state machine) +* register this callback via i2c_slave_register() + +Check the i2c-slave-eeprom driver as an example. + + +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 + slave address and enable slave specific interrupts. If you use runtime pm, you + should use pm_runtime_forbid() because your device usually needs to be powered + on always to be able to detect its slave address. When unregistering, do the + inverse of the above. + +* Catch the slave interrupts and send appropriate i2c_slave_events to the backend. + +Check the i2c-rcar driver as an example. + + +About ACK/NACK +-------------- + +It is good behaviour to always ACK the address phase, so the master knows if a +device is basically present or if it mysteriously disappeared. Using NACK to +state being busy is troublesome. SMBus demands to always ACK the address phase, +while the I2C specification is more loose on that. Most I2C controllers also +automatically ACK when detecting their slave addresses, so there is no option +to NACK them. For those reasons, this API does not support NACK in the address +phase. + +Currently, there is no slave event to report if the master did ACK or NACK a +byte when it reads from us. We could make this an optional event if the need +arises. However, cases should be extremely rare because the master is expected +to send STOP after that and we have an event for that. Also, keep in mind not +all I2C controllers have the possibility to report that event. + + +About buffers +------------- + +During development of this API, the question of using buffers instead of just +bytes came up. Such an extension might be possible, usefulness is unclear at +this time of writing. Some points to keep in mind when using buffers: + +* Buffers should be opt-in and slave drivers will always have to support + byte-based transactions as the ultimate fallback because this is how the + majority of HW works. + +* For backends simulating hardware registers, buffers are not helpful because + on writes an action should be immediately triggered. For reads, the data in + the buffer might get stale. + +* A master can send STOP at any time. For partially transferred buffers, this + means additional code to handle this exception. Such code tends to be + error-prone. + diff --git a/Documentation/i2c/summary b/Documentation/i2c/summary index 13ab076dcd92..809541ab352f 100644 --- a/Documentation/i2c/summary +++ b/Documentation/i2c/summary @@ -41,7 +41,3 @@ integrated than Algorithm and Adapter. 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). - -At this time, Linux only operates I2C (or SMBus) in master mode; you can't -use these APIs to make a Linux system behave as a slave/device, either to -speak a custom protocol or to emulate some other device. |