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| -rw-r--r-- | Documentation/i2c/instantiating-devices.rst | 97 |
1 files changed, 54 insertions, 43 deletions
diff --git a/Documentation/i2c/instantiating-devices.rst b/Documentation/i2c/instantiating-devices.rst index e823c4ad4e7f..665bf00792ba 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:: @@ -82,13 +55,51 @@ 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 :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 -------------------------------------------- |