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doc: driver-model: Convert livetree.txt to reST
Convert plain text documentation to reStructuredText format and add it to Sphinx TOC tree. No essential content change. Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
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Bin Meng
Tom Rini
parent
61c3e77330
commit
6c49c22846
@ -10,4 +10,5 @@ Driver Model
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fdt-fixup
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fs_firmware_loader
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i2c-howto
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livetree
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migration
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@ -1,5 +1,8 @@
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Driver Model with Live Device Tree
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==================================
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.. SPDX-License-Identifier: GPL-2.0+
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.. sectionauthor:: Simon Glass <sjg@chromium.org>
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Live Device Tree
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================
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Introduction
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@ -20,7 +23,7 @@ Motivation
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The flat device tree has several advantages:
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- it is the format produced by the device tree compiler, so no translation
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is needed
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is needed
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- it is fairly compact (e.g. there is no need for pointers)
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@ -53,12 +56,12 @@ The 'ofnode' type provides this. An ofnode can point to either a flat tree
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node (when the live tree node is not yet set up) or a livetree node. The
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caller of an ofnode function does not need to worry about these details.
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The main users of the information in a device tree are drivers. These have
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a 'struct udevice *' which is attached to a device tree node. Therefore it
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The main users of the information in a device tree are drivers. These have
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a 'struct udevice \*' which is attached to a device tree node. Therefore it
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makes sense to be able to read device tree properties using the
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'struct udevice *', rather than having to obtain the ofnode first.
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'struct udevice \*', rather than having to obtain the ofnode first.
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The 'dev_read_...()' interface provides this. It allows properties to be
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The 'dev_read\_...()' interface provides this. It allows properties to be
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easily read from the device tree using only a device pointer. Under the
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hood it uses ofnode so it works with both flat and live device trees.
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@ -85,6 +88,8 @@ converted to use the dev_read_() interface.
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For example, the old code may be like this:
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.. code-block:: c
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struct udevice *bus;
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const void *blob = gd->fdt_blob;
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int node = dev_of_offset(bus);
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@ -94,17 +99,21 @@ For example, the old code may be like this:
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The new code is:
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.. code-block:: c
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struct udevice *bus;
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i2c_bus->regs = (struct i2c_ctlr *)dev_read_addr(dev);
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plat->frequency = dev_read_u32_default(bus, "spi-max-frequency", 500000);
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The dev_read_...() interface is more convenient and works with both the
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The dev_read\_...() interface is more convenient and works with both the
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flat and live device trees. See include/dm/read.h for a list of functions.
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Where properties must be read from sub-nodes or other nodes, you must fall
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back to using ofnode. For example, for old code like this:
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.. code-block:: c
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const void *blob = gd->fdt_blob;
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int subnode;
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@ -115,6 +124,8 @@ back to using ofnode. For example, for old code like this:
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you should use:
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.. code-block:: c
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ofnode subnode;
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ofnode_for_each_subnode(subnode, dev_ofnode(dev)) {
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@ -128,8 +139,8 @@ Useful ofnode functions
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The internal data structures of the livetree are defined in include/dm/of.h :
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struct device_node - holds information about a device tree node
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struct property - holds information about a property within a node
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:struct device_node: holds information about a device tree node
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:struct property: holds information about a property within a node
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Nodes have pointers to their first property, their parent, their first child
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and their sibling. This allows nodes to be linked together in a hierarchical
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@ -149,20 +160,29 @@ For example it is invalid to call ofnode_to_no() when a flat tree is being
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used. Similarly it is not possible to call ofnode_to_offset() on a livetree
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node.
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ofnode_to_np() - converts ofnode to struct device_node *
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ofnode_to_offset() - converts ofnode to offset
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ofnode_to_np():
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converts ofnode to struct device_node *
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ofnode_to_offset():
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converts ofnode to offset
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no_to_ofnode() - converts node pointer to ofnode
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offset_to_ofnode() - converts offset to ofnode
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no_to_ofnode():
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converts node pointer to ofnode
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offset_to_ofnode():
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converts offset to ofnode
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Other useful functions:
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of_live_active() returns true if livetree is in use, false if flat tree
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ofnode_valid() return true if a given node is valid
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ofnode_is_np() returns true if a given node is a livetree node
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ofnode_equal() compares two ofnodes
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ofnode_null() returns a null ofnode (for which ofnode_valid() returns false)
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of_live_active():
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returns true if livetree is in use, false if flat tree
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ofnode_valid():
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return true if a given node is valid
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ofnode_is_np():
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returns true if a given node is a livetree node
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ofnode_equal():
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compares two ofnodes
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ofnode_null():
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returns a null ofnode (for which ofnode_valid() returns false)
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Phandles
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@ -199,13 +219,13 @@ the flat tree.
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Internal implementation
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-----------------------
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The dev_read_...() functions have two implementations. When
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The dev_read\_...() functions have two implementations. When
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CONFIG_DM_DEV_READ_INLINE is enabled, these functions simply call the ofnode
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functions directly. This is useful when livetree is not enabled. The ofnode
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functions call ofnode_is_np(node) which will always return false if livetree
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is disabled, just falling back to flat tree code.
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This optimisation means that without livetree enabled, the dev_read_...() and
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This optimisation means that without livetree enabled, the dev_read\_...() and
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ofnode interfaces do not noticeably add to code size.
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The CONFIG_DM_DEV_READ_INLINE option defaults to enabled when livetree is
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@ -225,7 +245,7 @@ Errors
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With a flat device tree, libfdt errors are returned (e.g. -FDT_ERR_NOTFOUND).
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For livetree normal 'errno' errors are returned (e.g. -ENOTFOUND). At present
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the ofnode and dev_read_...() functions return either one or other type of
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the ofnode and dev_read\_...() functions return either one or other type of
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error. This is clearly not desirable. Once tests are added for all the
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functions this can be tidied up.
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@ -236,23 +256,22 @@ Adding new access functions
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Adding a new function for device-tree access involves the following steps:
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- Add two dev_read() functions:
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- inline version in the read.h header file, which calls an ofnode
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function
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- standard version in the read.c file (or perhaps another file), which
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also calls an ofnode function
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- inline version in the read.h header file, which calls an ofnode function
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- standard version in the read.c file (or perhaps another file), which
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also calls an ofnode function
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The implementations of these functions can be the same. The purpose
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of the inline version is purely to reduce code size impact.
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The implementations of these functions can be the same. The purpose
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of the inline version is purely to reduce code size impact.
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- Add an ofnode function. This should call ofnode_is_np() to work out
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whether a livetree or flat tree is used. For the livetree it should
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call an of_...() function. For the flat tree it should call an
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fdt_...() function. The livetree version will be optimised out at
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compile time if livetree is not enabled.
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whether a livetree or flat tree is used. For the livetree it should
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call an of\_...() function. For the flat tree it should call an
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fdt\_...() function. The livetree version will be optimised out at
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compile time if livetree is not enabled.
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- Add an of_...() function for the livetree implementation. If a similar
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function is available in Linux, the implementation should be taken
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from there and modified as little as possible (generally not at all).
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- Add an of\_...() function for the livetree implementation. If a similar
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function is available in Linux, the implementation should be taken
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from there and modified as little as possible (generally not at all).
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Future work
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@ -265,8 +284,3 @@ of work to do to flesh this out:
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- support for livetree modification
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- addition of more access functions as needed
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- support for livetree in SPL and before relocation (if desired)
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--
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Simon Glass <sjg@chromium.org>
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5-Aug-17
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