projects / linux-block.git / blame
| Commit | Line | Data |
|---|---|---|
| b3fdd327 YS |
1 | Register-based I2C Bus Mux |
| 2 | ||
| 3 | This binding describes an I2C bus multiplexer that uses a single register | |
| 4 | to route the I2C signals. | |
| 5 | ||
| 6 | Required properties: | |
| 7 | - compatible: i2c-mux-reg | |
| 8 | - i2c-parent: The phandle of the I2C bus that this multiplexer's master-side | |
| 9 | port is connected to. | |
| 2e932849 SH |
10 | * Standard I2C mux properties. See i2c-mux.txt in this directory. |
| 11 | * I2C child bus nodes. See i2c-mux.txt in this directory. | |
| b3fdd327 YS |
12 | |
| 13 | Optional properties: | |
| 14 | - reg: this pair of <offset size> specifies the register to control the mux. | |
| 15 | The <offset size> depends on its parent node. It can be any memory-mapped | |
| 16 | address. The size must be either 1, 2, or 4 bytes. If reg is omitted, the | |
| 17 | resource of this device will be used. | |
| 18 | - little-endian: The existence indicates the register is in little endian. | |
| 19 | - big-endian: The existence indicates the register is in big endian. | |
| 20 | If both little-endian and big-endian are omitted, the endianness of the | |
| 21 | CPU will be used. | |
| 22 | - write-only: The existence indicates the register is write-only. | |
| 23 | - idle-state: value to set the muxer to when idle. When no value is | |
| 24 | given, it defaults to the last value used. | |
| 25 | ||
| 26 | Whenever an access is made to a device on a child bus, the value set | |
| 2e932849 | 27 | in the relevant node's reg property will be output to the register. |
| b3fdd327 YS |
28 | |
| 29 | If an idle state is defined, using the idle-state (optional) property, | |
| 30 | whenever an access is not being made to a device on a child bus, the | |
| 31 | register will be set according to the idle value. | |
| 32 | ||
| 33 | If an idle state is not defined, the most recently used value will be | |
| 34 | left programmed into the register. | |
| 35 | ||
| 36 | Example of a mux on PCIe card, the host is a powerpc SoC (big endian): | |
| 37 | ||
| 38 | i2c-mux { | |
| 39 | /* the <offset size> depends on the address translation | |
| 40 | * of the parent device. If omitted, device resource | |
| 41 | * will be used instead. The size is to determine | |
| 42 | * whether iowrite32, iowrite16, or iowrite8 will be used. | |
| 43 | */ | |
| 44 | reg = <0x6028 0x4>; | |
| 45 | little-endian; /* little endian register on PCIe */ | |
| 46 | compatible = "i2c-mux-reg"; | |
| 47 | #address-cells = <1>; | |
| 48 | #size-cells = <0>; | |
| 49 | i2c-parent = <&i2c1>; | |
| 50 | i2c@0 { | |
| 51 | reg = <0>; | |
| 52 | #address-cells = <1>; | |
| 53 | #size-cells = <0>; | |
| 54 | ||
| 55 | si5338: clock-generator@70 { | |
| 56 | compatible = "silabs,si5338"; | |
| 57 | reg = <0x70>; | |
| 58 | /* other stuff */ | |
| 59 | }; | |
| 60 | }; | |
| 61 | ||
| 62 | i2c@1 { | |
| 63 | /* data is written using iowrite32 */ | |
| 64 | reg = <1>; | |
| 65 | #address-cells = <1>; | |
| 66 | #size-cells = <0>; | |
| 67 | ||
| 68 | si5338: clock-generator@70 { | |
| 69 | compatible = "silabs,si5338"; | |
| 70 | reg = <0x70>; | |
| 71 | /* other stuff */ | |
| 72 | }; | |
| 73 | }; | |
| 74 | }; |