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Date:   Sun,  5 Jan 2020 23:50:07 +0100
From:   Luca Ceresoli <luca@...aceresoli.net>
To:     linux-doc@...r.kernel.org, linux-i2c@...r.kernel.org
Cc:     Luca Ceresoli <luca@...aceresoli.net>,
        Wolfram Sang <wsa@...-dreams.de>,
        Peter Rosin <peda@...ntia.se>, linux-kernel@...r.kernel.org
Subject: [PATCH 21/26] docs: i2c: instantiating-devices: rearrange static instatiation

Among the "static" instantiation methods the "board file" method is
described first. Move it as last, since it is being replaced by the other
methods.

Also fix subsubsection heading syntax and remove the "Method 1[abc]"
prefix as the subsubsection structure clarifies the logical hierarchy.

Signed-off-by: Luca Ceresoli <luca@...aceresoli.net>
---
 Documentation/i2c/instantiating-devices.rst | 98 ++++++++++++---------
 1 file changed, 54 insertions(+), 44 deletions(-)

diff --git a/Documentation/i2c/instantiating-devices.rst b/Documentation/i2c/instantiating-devices.rst
index 5debaafef64d..cbcafb36b417 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::
 
@@ -81,14 +54,51 @@ Here, two devices are attached to the bus using a speed of 100kHz. For
 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
 --------------------------------------------
 
-- 
2.24.1

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