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-rw-r--r--Documentation/i2c/instantiating-devices.rst97
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
--------------------------------------------