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https://github.com/AsahiLinux/u-boot
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Merge git://git.denx.de/u-boot-dm
This commit is contained in:
Tom Rini
commit
ced0fd938d
4 changed files with 303 additions and 5 deletions
8
.gitignore
vendored
8
.gitignore
vendored
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@ -57,6 +57,14 @@ fit-dtb.blob
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/include/config/
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/include/generated/
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# Since "ee95d10 fdt: Build the new python libfdt module", a number of
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# build artifacts and intermediated from the python libfdt module are
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# installed into the /tools directory.
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/tools/_libfdt.so
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/tools/libfdt.py
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/tools/libfdt.pyc
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/tools/libfdt_wrap.c
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# stgit generated dirs
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patches-*
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.stgit-edit.txt
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@ -284,16 +284,14 @@ static int do_fdt(cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[])
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len = 0;
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} else {
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ptmp = fdt_getprop(working_fdt, nodeoffset, prop, &len);
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if (!ptmp) {
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printf("prop (%s) not found!\n", prop);
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return 1;
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}
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if (len > SCRATCHPAD) {
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printf("prop (%d) doesn't fit in scratchpad!\n",
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len);
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return 1;
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}
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memcpy(data, ptmp, len);
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if (ptmp != NULL)
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memcpy(data, ptmp, len);
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ret = fdt_parse_prop(&argv[4], argc - 4, data, &len);
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if (ret != 0)
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return ret;
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20
doc/driver-model/MIGRATION.txt
Normal file
20
doc/driver-model/MIGRATION.txt
Normal file
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@ -0,0 +1,20 @@
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Migration Schedule
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====================
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U-Boot has been migrating to a new driver model since its introduction in
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2014. This file describes the schedule for deprecation of pre-driver-model
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features.
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CONFIG_BLK
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----------
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Status: In progress
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Deadline: 2018.05
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Maintainers should submit patches for enabling CONFIG_BLK on all boards in
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time for inclusion in the 2018.05 release. Boards not converted by this
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time may be removed in a subsequent release.
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Note that this implies use of driver model for all block devices (e.g.
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MMC, USB, SCSI, SATA).
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272
doc/driver-model/livetree.txt
Normal file
272
doc/driver-model/livetree.txt
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@ -0,0 +1,272 @@
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Driver Model with Live Device Tree
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==================================
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Introduction
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------------
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Traditionally U-Boot has used a 'flat' device tree. This means that it
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reads directly from the device tree binary structure. It is called a flat
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device tree because nodes are listed one after the other, with the
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hierarchy detected by tags in the format.
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This document describes U-Boot's support for a 'live' device tree, meaning
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that the tree is loaded into a hierarchical data structure within U-Boot.
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Motivation
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----------
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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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- it is fairly compact (e.g. there is no need for pointers)
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- it is accessed by the libfdt library, which is well tested and stable
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However the flat device tree does have some limitations. Adding new
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properties can involve copying large amounts of data around to make room.
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The overall tree has a fixed maximum size so sometimes the tree must be
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rebuilt in a new location to create more space. Even if not adding new
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properties or nodes, scanning the tree can be slow. For example, finding
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the parent of a node is a slow process. Reading from nodes involves a
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small amount parsing which takes a little time.
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Driver model scans the entire device tree sequentially on start-up which
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avoids the worst of the flat tree's limitations. But if the tree is to be
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modified at run-time, a live tree is much faster. Even if no modification
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is necessary, parsing the tree once and using a live tree from then on
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seems to save a little time.
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Implementation
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--------------
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In U-Boot a live device tree ('livetree') is currently supported only
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after relocation. Therefore we need a mechanism to specify a device
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tree node regardless of whether it is in the flat tree or livetree.
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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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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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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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Enabling livetree
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-----------------
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CONFIG_OF_LIVE enables livetree. When this option is enabled, the flat
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tree will be used in SPL and before relocation in U-Boot proper. Just
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before relocation a livetree is built, and this is used for U-Boot proper
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after relocation.
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Most checks for livetree use CONFIG_IS_ENABLED(OF_LIVE). This means that
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for SPL, the CONFIG_SPL_OF_LIVE option is checked. At present this does
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not exist, since SPL does not support livetree.
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Porting drivers
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---------------
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Many existing drivers use the fdtdec interface to read device tree
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properties. This only works with a flat device tree. The drivers should be
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converted to use the dev_read_() interface.
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For example, the old code may be like this:
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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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i2c_bus->regs = (struct i2c_ctlr *)devfdt_get_addr(dev);
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plat->frequency = fdtdec_get_int(blob, node, "spi-max-frequency", 500000);
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The new code is:
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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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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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const void *blob = gd->fdt_blob;
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int subnode;
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fdt_for_each_subnode(subnode, blob, dev_of_offset(dev)) {
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freq = fdtdec_get_int(blob, node, "spi-max-frequency", 500000);
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...
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}
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you should use:
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ofnode subnode;
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ofnode_for_each_subnode(subnode, dev_ofnode(dev)) {
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freq = ofnode_read_u32(node, "spi-max-frequency", 500000);
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...
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}
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Useful ofnode functions
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-----------------------
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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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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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tree.
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Properties have pointers to the next property. This allows all properties of
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a node to be linked together in a chain.
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It should not be necessary to use these data structures in normal code. In
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particular, you should refrain from using functions which access the livetree
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directly, such as of_read_u32(). Use ofnode functions instead, to allow your
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code to work with a flat tree also.
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Some conversion functions are used internally. Generally these are not needed
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for driver code. Note that they will not work if called in the wrong context.
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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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no_to_ofnode() - converts node pointer to ofnode
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offset_to_ofnode() - 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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Phandles
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--------
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There is full phandle support for live tree. All functions make use of
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struct ofnode_phandle_args, which has an ofnode within it. This supports both
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livetree and flat tree transparently. See for example
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ofnode_parse_phandle_with_args().
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Reading addresses
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-----------------
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You should use dev_read_addr() and friends to read addresses from device-tree
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nodes.
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fdtdec
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------
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The existing fdtdec interface will eventually be retired. Please try to avoid
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using it in new code.
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Modifying the livetree
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----------------------
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This is not currently supported. Once implemented it should provide a much
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more efficient implementation for modification of the device tree than using
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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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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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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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disabled.
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Most livetree code comes directly from Linux and is modified as little as
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possible. This is deliberate since this code is fairly stable and does what
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we want. Some features (such as get/put) are not supported. Internal macros
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take care of removing these features silently.
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Within the of_access.c file there are pointers to the alias node, the chosen
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node and the stdout-path alias.
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Errors
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------
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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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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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Adding new access functions
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---------------------------
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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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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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- 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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-----------
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Live tree support was introduced in U-Boot 2017.07. There is still quite a bit
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of work to do to flesh this out:
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- tests for all access functions
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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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