projects / linux-2.6-block.git / blame
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1 | Generic device tree bindings for I2C busses |
| 2 | =========================================== | |
| 3 | ||
| 4 | This document describes generic bindings which can be used to describe I2C | |
| 5 | busses in a device tree. | |
| 6 | ||
| 7 | Required properties | |
| 8 | ------------------- | |
| 9 | ||
| 10 | - #address-cells - should be <1>. Read more about addresses below. | |
| 11 | - #size-cells - should be <0>. | |
| 12 | - compatible - name of I2C bus controller following generic names | |
| 13 | recommended practice. | |
| 14 | ||
| 3fffd128 | 15 | For other required properties e.g. to describe register sets, |
| 7a59b00a WS |
16 | clocks, etc. check the binding documentation of the specific driver. |
| 17 | ||
| 18 | The cells properties above define that an address of children of an I2C bus | |
| 19 | are described by a single value. This is usually a 7 bit address. However, | |
| 20 | flags can be attached to the address. I2C_TEN_BIT_ADDRESS is used to mark a 10 | |
| 21 | bit address. It is needed to avoid the ambiguity between e.g. a 7 bit address | |
| 22 | of 0x50 and a 10 bit address of 0x050 which, in theory, can be on the same bus. | |
| 23 | Another flag is I2C_OWN_SLAVE_ADDRESS to mark addresses on which we listen to | |
| 24 | be devices ourselves. | |
| 25 | ||
| 26 | Optional properties | |
| 27 | ------------------- | |
| 28 | ||
| 29 | These properties may not be supported by all drivers. However, if a driver | |
| 30 | wants to support one of the below features, it should adapt the bindings below. | |
| 31 | ||
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32 | - clock-frequency |
| 33 | frequency of bus clock in Hz. | |
| 3fffd128 | 34 | |
| 99b809d7 WS |
35 | - i2c-scl-falling-time-ns |
| 36 | Number of nanoseconds the SCL signal takes to fall; t(f) in the I2C | |
| 37 | specification. | |
| 38 | ||
| 39 | - i2c-scl-internal-delay-ns | |
| 40 | Number of nanoseconds the IP core additionally needs to setup SCL. | |
| 41 | ||
| 42 | - i2c-scl-rising-time-ns | |
| 43 | Number of nanoseconds the SCL signal takes to rise; t(r) in the I2C | |
| 44 | specification. | |
| 45 | ||
| 46 | - i2c-sda-falling-time-ns | |
| 47 | Number of nanoseconds the SDA signal takes to fall; t(f) in the I2C | |
| 48 | specification. | |
| 49 | ||
| 50 | - interrupts | |
| 51 | interrupts used by the device. | |
| 52 | ||
| 53 | - interrupt-names | |
| 54 | "irq" and "wakeup" names are recognized by I2C core, other names are | |
| 55 | left to individual drivers. | |
| 56 | ||
| 57 | - wakeup-source | |
| 58 | device can be used as a wakeup source. | |
| 3fffd128 DT |
59 | |
| 60 | Binding may contain optional "interrupts" property, describing interrupts | |
| 61 | used by the device. I2C core will assign "irq" interrupt (or the very first | |
| 62 | interrupt if not using interrupt names) as primary interrupt for the slave. | |
| 63 | ||
| 64 | Also, if device is marked as a wakeup source, I2C core will set up "wakeup" | |
| 65 | interrupt for the device. If "wakeup" interrupt name is not present in the | |
| 66 | binding, then primary interrupt will be used as wakeup interrupt. |