projects / deliverable / linux.git / blame
| Commit | Line | Data |
|---|---|---|
| 9b7a0c40 MR |
1 | GPIO-based I2C Bus Mux |
| 2 | ||
| 3 | This binding describes an I2C bus multiplexer that uses GPIOs to | |
| 4 | route the I2C signals. | |
| 5 | ||
| 6 | +-----+ +-----+ | |
| 7 | | dev | | dev | | |
| 8 | +------------+ +-----+ +-----+ | |
| 9 | | SoC | | | | |
| 10 | | | /--------+--------+ | |
| 11 | | +------+ | +------+ child bus A, on GPIO value set to 0 | |
| 12 | | | I2C |-|--| Mux | | |
| 13 | | +------+ | +--+---+ child bus B, on GPIO value set to 1 | |
| 14 | | | | \----------+--------+--------+ | |
| 15 | | +------+ | | | | | | |
| 16 | | | GPIO |-|-----+ +-----+ +-----+ +-----+ | |
| 17 | | +------+ | | dev | | dev | | dev | | |
| 18 | +------------+ +-----+ +-----+ +-----+ | |
| 19 | ||
| 20 | Required properties: | |
| 21 | - compatible: i2c-mux-gpio | |
| 22 | - i2c-parent: The phandle of the I2C bus that this multiplexer's master-side | |
| 23 | port is connected to. | |
| 24 | - mux-gpios: list of gpios used to control the muxer | |
| 2e932849 SH |
25 | * Standard I2C mux properties. See i2c-mux.txt in this directory. |
| 26 | * I2C child bus nodes. See i2c-mux.txt in this directory. | |
| 9b7a0c40 MR |
27 | |
| 28 | Optional properties: | |
| 29 | - idle-state: value to set the muxer to when idle. When no value is | |
| 30 | given, it defaults to the last value used. | |
| 31 | ||
| 32 | For each i2c child node, an I2C child bus will be created. They will | |
| 33 | be numbered based on their order in the device tree. | |
| 34 | ||
| 35 | Whenever an access is made to a device on a child bus, the value set | |
| 2e932849 | 36 | in the relevant node's reg property will be output using the list of |
| 9b7a0c40 MR |
37 | GPIOs, the first in the list holding the least-significant value. |
| 38 | ||
| 39 | If an idle state is defined, using the idle-state (optional) property, | |
| 40 | whenever an access is not being made to a device on a child bus, the | |
| 41 | GPIOs will be set according to the idle value. | |
| 42 | ||
| 43 | If an idle state is not defined, the most recently used value will be | |
| 44 | left programmed into hardware whenever no access is being made to a | |
| 45 | device on a child bus. | |
| 46 | ||
| 47 | Example: | |
| 48 | i2cmux { | |
| 49 | compatible = "i2c-mux-gpio"; | |
| 50 | #address-cells = <1>; | |
| 51 | #size-cells = <0>; | |
| 52 | mux-gpios = <&gpio1 22 0 &gpio1 23 0>; | |
| 53 | i2c-parent = <&i2c1>; | |
| 54 | ||
| 55 | i2c@1 { | |
| 56 | reg = <1>; | |
| 57 | #address-cells = <1>; | |
| 58 | #size-cells = <0>; | |
| 59 | ||
| 60 | ssd1307: oled@3c { | |
| 61 | compatible = "solomon,ssd1307fb-i2c"; | |
| 62 | reg = <0x3c>; | |
| 63 | pwms = <&pwm 4 3000>; | |
| 64 | reset-gpios = <&gpio2 7 1>; | |
| 65 | reset-active-low; | |
| 66 | }; | |
| 67 | }; | |
| 68 | ||
| 69 | i2c@3 { | |
| 70 | reg = <3>; | |
| 71 | #address-cells = <1>; | |
| 72 | #size-cells = <0>; | |
| 73 | ||
| 74 | pca9555: pca9555@20 { | |
| 75 | compatible = "nxp,pca9555"; | |
| 76 | gpio-controller; | |
| 77 | #gpio-cells = <2>; | |
| 78 | reg = <0x20>; | |
| 79 | }; | |
| 80 | }; | |
| 81 | }; |