[PATCH v4 33/33] bootstd: doc: Add documentation

Simon Glass
2022-03-06T12:55:47Z

Add documentation for this feature, including the commands and full
devicetree bindings.

Signed-off-by: Simon Glass <sjg@chromium.org>
---

Changes in v4:
- Update docs for typos that have been fixed

Changes in v3:
- Update docs for "bootmeths" and "boot_targets" env vars

MAINTAINERS | 4 +
doc/develop/bootstd.rst | 638 ++++++++++++++++++++++++++
doc/develop/distro.rst | 3 +
doc/develop/index.rst | 1 +
doc/device-tree-bindings/bootdev.txt | 18 +
doc/device-tree-bindings/bootmeth.txt | 31 ++
doc/device-tree-bindings/bootstd.txt | 8 +
doc/usage/bootdev.rst | 135 ++++++
doc/usage/bootflow.rst | 427 +++++++++++++++++
doc/usage/bootmeth.rst | 108 +++++
doc/usage/index.rst | 3 +
11 files changed, 1376 insertions(+)
create mode 100644 doc/develop/bootstd.rst
create mode 100644 doc/device-tree-bindings/bootmeth.txt
create mode 100644 doc/usage/bootdev.rst
create mode 100644 doc/usage/bootflow.rst
create mode 100644 doc/usage/bootmeth.rst

diff --git a/MAINTAINERS b/MAINTAINERS
index b15d3694fa..94d80042ef 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -691,6 +691,10 @@ F: boot/bootmeth*.c
F: boot/bootstd.c
F: cmd/bootdev.c
F: cmd/bootflow.c
+F: doc/develop/bootstd.rst
+F: doc/usage/bootdev.rst
+F: doc/usage/bootflow.rst
+F: doc/usage/bootmeth.rst
F: drivers/mmc/mmc_bootdev.c
F: include/bootdev.h
F: include/bootflow.h
diff --git a/doc/develop/bootstd.rst b/doc/develop/bootstd.rst
new file mode 100644
index 0000000000..f7f7003da5
--- /dev/null
+++ b/doc/develop/bootstd.rst
@@ -0,0 +1,638 @@
+.. SPDX-License-Identifier: GPL-2.0+:
+
+U-Boot Standard Boot
+====================
+
+Introduction
+------------
+
+Standard boot provides a built-in way for U-Boot to automatically boot
+an Operating System without custom scripting and other customisation. It
+introduces the following concepts:
+
+ - bootdev - a device which can hold or access a distro (e.g. MMC, Ethernet)
+ - bootmeth - a method to scan a bootdev to find bootflows (e.g. distro boot)
+ - bootflow - a description of how to boot (provided by the distro)
+
+For Linux, the distro (Linux distribution, e.g. Debian, Fedora) is responsible
+for creating a bootflow for each kernel combination that it wants to offer.
+These bootflows are stored on media so they can be discovered by U-Boot. This
+feature is typically called `distro boot` (see :doc:`distro`) because it is
+a way for distributions to boot on any hardware.
+
+Traditionally U-Boot has relied on scripts to implement this feature. See
+disto_boodcmd_ for details. This is done because U-Boot has no native support
+for scanning devices. While the scripts work remarkably well, they can be hard
+to understand and extend, and the feature does not include tests. They are also
+making it difficult to move away from ad-hoc CONFIGs, since they are implemented
+using the environment and a lot of #defines.
+
+Standard boot is a generalisation of distro boot. It provides a more built-in
+way to boot with U-Boot. The feature is extensible to different Operating
+Systems (such as Chromium OS) and devices (beyond just block and network
+devices). It supports EFI boot and EFI bootmgr too.
+
+
+Bootflow
+--------
+
+A bootflow is a file that describes how to boot a distro. Conceptually there can
+be different formats for that file but at present U-Boot only supports the
+BootLoaderSpec_ format. which looks something like this::
+
+ menu autoboot Welcome to Fedora-Workstation-armhfp-31-1.9. Automatic boot in # second{,s}. Press a key for options.
+ menu title Fedora-Workstation-armhfp-31-1.9 Boot Options.
+ menu hidden
+
+ label Fedora-Workstation-armhfp-31-1.9 (5.3.7-301.fc31.armv7hl)
+ kernel /vmlinuz-5.3.7-301.fc31.armv7hl
+ append ro root=UUID=9732b35b-4cd5-458b-9b91-80f7047e0b8a rhgb quiet LANG=en_US.UTF-8 cma=192MB cma=256MB
+ fdtdir /dtb-5.3.7-301.fc31.armv7hl/
+ initrd /initramfs-5.3.7-301.fc31.armv7hl.img
+
+As you can see it specifies a kernel, a ramdisk (initrd) and a directory from
+which to load devicetree files. The details are described in disto_boodcmd_.
+
+The bootflow is provided by the distro. It is not part of U-Boot. U-Boot's job
+is simply to interpret the file and carry out the instructions. This allows
+distros to boot on essentially any device supported by U-Boot.
+
+Typically the first available bootflow is selected and booted. If that fails,
+then the next one is tried.
+
+
+Bootdev
+-------
+
+Where does U-Boot find the media that holds the operating systems? That is the
+job of bootdev. A bootdev is simply a layer on top of a media device (such as
+MMC, NVMe). The bootdev accesses the device, including partitions and
+filesystems that might contain things related to an operating system.
+
+For example, an MMC bootdev provides access to the individual partitions on the
+MMC device. It scans through these to find filesystems, then provides a list of
+these for consideration.
+
+
+Bootmeth
+--------
+
+Once the list of filesystems is provided, how does U-Boot find the bootflow
+files in these filesystems. That is the job of bootmeth. Each boot method has
+its own way of doing this.
+
+For example, the distro bootmeth simply looks through the provided filesystem
+for a file called `extlinux/extlinux.conf`. This files constitutes a bootflow.
+If the distro bootmeth is used on multiple partitions it may produce multiple
+bootflows.
+
+Note: it is possible to have a bootmeth that uses a partition or a whole device
+directly, but it is more common to use a filesystem.
+
+
+Boot process
+------------
+
+U-Boot tries to use the 'lazy init' approach whereever possible and distro boot
+is no exception. The algorithm is::
+
+ while (get next bootdev)
+ while (get next bootmeth)
+ while (get next bootflow)
+ try to boot it
+
+So U-Boot works its way through the bootdevs, trying each bootmeth in turn to
+obtain bootflows, until it either boots or exhausts the available options.
+
+Instead of 500 lines of #defines and a 4KB boot script, all that is needed is
+the following command::
+
+ bootflow scan -lb
+
+which scans for available bootflows, optionally listing each find it finds (-l)
+and trying to boot it (-b).
+
+
+Controlling ordering
+--------------------
+
+Several options are available to control the ordering of boot scanning:
+
+
+boot_targets
+~~~~~~~~~~~~
+
+This environment variable can be used to control the list of bootdevs searched
+and their ordering, for example::
+
+ setenv boot_targets "mmc0 mmc1 usb pxe"
+
+Entries may be removed or re-ordered in this list to affect the boot order. If
+the variable is empty, the default ordering is used, based on the priority of
+bootdevs and their sequence numbers.
+
+
+bootmeths
+~~~~~~~~~
+
+This environment variable can be used to control the list of bootmeths used and
+their ordering for example::
+
+ setenv bootmeths "syslinux efi"
+
+Entries may be removed or re-ordered in this list to affect the order the
+bootmeths are tried on each bootdev. If the variable is empty, the default
+ordering is used, based on the bootmeth sequence numbers, which can be
+controlled by aliases.
+
+The :ref:`usage/bootmeth:bootmeth command` (`bootmeth order`) operates in the
+same way as setting this variable.
+
+
+Bootdev uclass
+--------------
+
+The bootdev uclass provides an simple API call to obtain a bootflows from a
+device::
+
+ int bootdev_get_bootflow(struct udevice *dev, struct bootflow_iter *iter,
+ struct bootflow *bflow);
+
+This takes a iterator which indicates the bootdev, partition and bootmeth to
+use. It returns a bootflow. This is the core of the bootdev implementation. The
+bootdev drivers that implement this differ depending on the media they are
+reading from, but each is responsible for returning a valid bootflow if
+available.
+
+A helper called `bootdev_find_in_blk()` makes it fairly easy to implement this
+function for each media device uclass, in a few lines of code.
+
+
+Bootdev drivers
+---------------
+
+A bootdev driver is typically fairly simple. Here is one for mmc::
+
+ static int mmc_get_bootflow(struct udevice *dev, struct bootflow_iter *iter,
+ struct bootflow *bflow)
+ {
+ struct udevice *mmc_dev = dev_get_parent(dev);
+ struct udevice *blk;
+ int ret;
+
+ ret = mmc_get_blk(mmc_dev, &blk);
+ /*
+ * If there is no media, indicate that no more partitions should be
+ * checked
+ */
+ if (ret == -EOPNOTSUPP)
+ ret = -ESHUTDOWN;
+ if (ret)
+ return log_msg_ret("blk", ret);
+ assert(blk);
+ ret = bootdev_find_in_blk(dev, blk, iter, bflow);
+ if (ret)
+ return log_msg_ret("find", ret);
+
+ return 0;
+ }
+
+ static int mmc_bootdev_bind(struct udevice *dev)
+ {
+ struct bootdev_uc_plat *ucp = dev_get_uclass_plat(dev);
+
+ ucp->prio = BOOTDEVP_0_INTERNAL_FAST;
+
+ return 0;
+ }
+
+ struct bootdev_ops mmc_bootdev_ops = {
+ .get_bootflow = mmc_get_bootflow,
+ };
+
+ static const struct udevice_id mmc_bootdev_ids[] = {
+ { .compatible = "u-boot,bootdev-mmc" },
+ { }
+ };
+
+ U_BOOT_DRIVER(mmc_bootdev) = {
+ .name = "mmc_bootdev",
+ .id = UCLASS_BOOTDEV,
+ .ops = &mmc_bootdev_ops,
+ .bind = mmc_bootdev_bind,
+ .of_match = mmc_bootdev_ids,
+ };
+
+The implementation of the `get_bootflow()` method is simply to obtain the
+block device and call a bootdev helper function to do the rest. The
+implementation of `bootdev_find_in_blk()` checks the partition table, and
+attempts to read a file from a filesystem on the partition number given by the
+`@iter->part` parameter.
+
+Each bootdev has a priority, which indicates the order in which it is used.
+Faster bootdevs are used first, since they are more likely to be able to boot
+the device quickly.
+
+
+Device hierarchy
+----------------
+
+A bootdev device is a child of the media device. In this example, you can see
+that the bootdev is a sibling of the block device and both are children of
+media device::
+
+ mmc 0 [ + ] bcm2835-sdhost | |-- mmc@7e202000
+ blk 0 [ + ] mmc_blk | | |-- mmc@7e202000.blk
+ bootdev 0 [ ] mmc_bootdev | | `-- mmc@7e202000.bootdev
+ mmc 1 [ + ] sdhci-bcm2835 | |-- sdhci@7e300000
+ blk 1 [ ] mmc_blk | | |-- sdhci@7e300000.blk
+ bootdev 1 [ ] mmc_bootdev | | `-- sdhci@7e300000.bootdev
+
+The bootdev device is typically created automatically in the media uclass'
+`post_bind()` method by calling `bootdev_setup_for_dev()`. The code typically
+something like this::
+
+ ret = bootdev_setup_for_dev(dev, "eth_bootdev");
+ if (ret)
+ return log_msg_ret("bootdev", ret);
+
+Here, `eth_bootdev` is the name of the Ethernet bootdev driver and `dev`
+is the ethernet device. This function is safe to call even if standard boot is
+not enabled, since it does nothing in that case. It can be added to all uclasses
+which implement suitable media.
+
+
+The bootstd device
+------------------
+
+Standard boot requires a single instance of the bootstd device to make things
+work. This includes global information about the state of standard boot. See
+`struct bootstd_priv` for this structure, accessed with `bootstd_get_priv()`.
+
+Within the devicetree, if you add bootmeth devices or a system bootdev, they
+should be children of the bootstd device. See `arch/sandbox/dts/test.dts` for
+an example of this.
+
+
+The system bootdev
+------------------
+
+Some bootmeths don't operate on individual bootdevs, but on the whole system.
+For example, the EFI boot manager does its own device scanning and does not
+make use of the bootdev devices. Such bootmeths can make use of the system
+bootdev, typically considered last, after everything else has been tried.
+
+
+.. _`Automatic Devices`:
+
+Automatic devices
+-----------------
+
+It is possible to define all the required devices in the devicetree manually,
+but it is not necessary. The bootstd uclass includes a `dm_scan_other()`
+function which creates the bootstd device if not found. If no bootmeth devices
+are found at all, it creates one for each available bootmeth driver as well as a
+system bootdev.
+
+If your devicetree has any bootmeth device it must have all of them that you
+want to use, as well as the system bootdev if needed, since no bootmeth devices
+will be created automatically in that case.
+
+
+Using devicetree
+----------------
+
+If a bootdev is complicated or needs configuration information, it can be
+added to the devicetree as a child of the media device. For example, imagine a
+bootdev which reads a bootflow from SPI flash. The devicetree fragment might
+look like this::
+
+ spi@0 {
+ flash@0 {
+ reg = <0>;
+ compatible = "spansion,m25p16", "jedec,spi-nor";
+ spi-max-frequency = <40000000>;
+
+ bootdev {
+ compatible = "u-boot,sf-bootdev";
+ offset = <0x2000>;
+ size = <0x1000>;
+ };
+ };
+ };
+
+The `sf-bootdev` driver can implement a way to read from the SPI flash, using
+the offset and size provided, and return that bootflow file back to the caller.
+When distro boot wants to read the kernel it calls disto_getfile() which must
+provide a way to read from the SPI flash. See `distro_boot()` at distro_boot_
+for more details.
+
+Of course this is all internal to U-Boot. All the distro sees is another way
+to boot.
+
+
+Configuration
+-------------
+
+Standard boot is enabled with `CONFIG_BOOTSTD`. Each bootmeth has its own CONFIG
+option also. For example, `CONFIG_BOOTMETH_DISTRO` enables support for distro
+boot from a disk.
+
+
+Available bootmeth drivers
+--------------------------
+
+Bootmeth drivers are provided for:
+
+ - distro boot from a disk (syslinux)
+ - distro boot from a network (PXE)
+ - EFI boot using bootefi
+ - EFI boot using boot manager
+
+
+Command interface
+-----------------
+
+Three commands are available:
+
+`bootdev`
+ Allows listing of available bootdevs, selecting a particular one and
+ getting information about it. See :doc:`../usage/bootdev`
+
+`bootflow`
+ Allows scanning one or more bootdevs for bootflows, listing available
+ bootflows, selecting one, obtaining information about it and booting it.
+ See :doc:`../usage/bootflow`
+
+`bootmeth`
+ Allow listing of available bootmethds and setting the order in which they
+ are tried. See :doc:`../usage/bootmeth`
+
+.. _BootflowStates:
+
+Bootflow states
+---------------
+
+Here is a list of states that a bootflow can be in:
+
+======= =======================================================================
+State Meaning
+======= =======================================================================
+base Starting-out state, indicates that no media/partition was found. For an
+ SD card socket it may indicate that the card is not inserted.
+media Media was found (e.g. SD card is inserted) but no partition information
+ was found. It might lack a partition table or have a read error.
+part Partition was found but a filesystem could not be read. This could be
+ because the partition does not hold a filesystem or the filesystem is
+ very corrupted.
+fs Filesystem was found but the file could not be read. It could be
+ missing or in the wrong subdirectory.
+file File was found and its size detected, but it could not be read. This
+ could indicate filesystem corruption.
+ready File was loaded and is ready for use. In this state the bootflow is
+ ready to be booted.
+======= =======================================================================
+
+
+Theory of operation
+-------------------
+
+This describes how standard boot progresses through to booting an operating
+system.
+
+To start. all the necessary devices must be bound, including bootstd, which
+provides the top-level `struct bootstd_priv` containing optional configuration
+information. The bootstd device is also holds the various lists used while
+scanning. This step is normally handled automatically by driver model, as
+described in `Automatic Devices`_.
+
+Bootdevs are also required, to provide access to the media to use. These are not
+useful by themselves: bootmeths are needed to provide the means of scanning
+those bootdevs. So, all up, we need a single bootstd device, one or more bootdev
+devices and one or more bootmeth devices.
+
+Once these are ready, typically a `bootflow scan` command is issued. This kicks
+of the iteration process, which involves looking through the bootdevs and their
+partitions one by one to find bootflows.
+
+Iteration is kicked off using `bootflow_scan_first()`, which calls
+`bootflow_scan_bootdev()`.
+
+The iterator is set up with `bootflow_iter_init()`. This simply creates an
+empty one with the given flags. Flags are used to control whether each
+iteration is displayed, whether to return iterations even if they did not result
+in a valid bootflow, whether to iterate through just a single bootdev, etc.
+
+Then the ordering of bootdevs is determined, by `bootdev_setup_iter_order()`. By
+default, the bootdevs are used in the order specified by the `boot_targets`
+environment variable (e.g. "mmc2 mmc0 usb"). If that is missing then their
+sequence order is used, as determined by the `/aliases` node, or failing that
+their order in the devicetree. For BOOTSTD_FULL, if there is a `bootdev-order`
+property in the bootstd node, then this is used as a final fallback. In any
+case, the iterator ends up with a `dev_order` array containing the bootdevs that
+are going to be used, with `num_devs` set to the number of bootdevs and
+`cur_dev` starting at 0.
+
+Next, the ordering of bootdevs is determined, by `bootmeth_setup_iter_order()`.
+By default the ordering is again by sequence number, i.e. the `/aliases` node,
+or failing that the order in the devicetree. But the `bootmeth order` command
+or `bootmeths` environment variable can be used to set up an ordering. If that
+has been done, the ordering is in `struct bootstd_priv`, so that ordering is
+simply copied into the iterator. Either way, the `method_order` array it set up,
+along with `num_methods`. Then `cur_method` is set to 0.
+
+At this point the iterator is ready to use, with the first bootdev and bootmeth
+selected. All the other fields are 0. This means that the current partition is
+0, which is taken to mean the whole device, since partition numbers start at 1.
+It also means that `max_part` is 0, i.e. the maximum partition number we know
+about is 0, meaning that, as far as we know, there is no partition table on this
+bootdev.
+
+With the iterator ready, `bootflow_scan_bootdev()` checks whether the current
+settings produce a valid bootflow. This is handled by `bootflow_check()`, which
+either returns 0 (if it got something) or an error if not (more on that later).
+If the `BOOTFLOWF_ALL` iterator flag is set, even errors are returned as
+incomplete bootflows, but normally an error results in moving onto the next
+iteration.
+
+The `bootflow_scan_next()` function handles moving onto the next iteration and
+checking it. In fact it sits in a loop doing that repeatedly until it finds
+something it wants to return.
+
+The actual 'moving on' part is implemented in `iter_incr()`. This is a very
+simple function. It increments the first counter. If that hits its maximum, it
+sets it to zero and increments the second counter. You can think of all the
+counters together as a number with three digits which increment in order, with
+the least-sigificant digit on the right, counting like this:
+
+ ======== ======= =======
+ bootdev part method
+ ======== ======= =======
+ 0 0 0
+ 0 0 1
+ 0 0 2
+ 0 1 0
+ 0 1 1
+ 0 1 1
+ 1 0 0
+ 1 0 1
+ ======== ======= =======
+
+The maximum value for `method` is `num_methods - 1` so when it exceeds that, it
+goes back to 0 and the next `part` is considered. The maximum value for that is
+`max_part`, which is initially zero for all bootdevs. If we find a partition
+table on that bootdev, `max_part` can be updated during the iteration to a
+higher value - see `bootdev_find_in_blk()` for that, described later. If that
+exceeds its maximum, then the next bootdev is used. In this way, iter_incr()
+works its way through all possibilities, moving forward one each time it is
+called.
+
+There is no expectation that iteration will actually finish. Quite often a
+valid bootflow is found early on. With `bootflow scan -b`, that causes the
+bootflow to be immediately booted. Assuming it is successful, the iteration never
+completes.
+
+Also note that the iterator hold the **current** combination being considered.
+So when `iter_incr()` is called, it increments to the next one and returns it,
+the new **current** combination.
+
+Note also the `err` field in `struct bootflow_iter`. This is normally 0 and has
+thus has no effect on `iter_inc()`. But if it is non-zero, signalling an error,
+it indicates to the iterator what it should do when called. It can force moving
+to the next partition, or bootdev, for example. The special values
+`BF_NO_MORE_PARTS` and `BF_NO_MORE_DEVICES` handle this. When `iter_incr` sees
+`BF_NO_MORE_PARTS` it knows that it should immediately move to the next bootdev.
+When it sees `BF_NO_MORE_DEVICES` it knows that there is nothing more it can do
+so it should immediately return. The caller of `iter_incr()` is responsible for
+updating the `err` field, based on the return value it sees.
+
+The above describes the iteration process at a high level. It is basically a
+very simple increment function with a checker called `bootflow_check()` that
+checks the result of each iteration generated, to determine whether it can
+produce a bootflow.
+
+So what happens inside of `bootflow_check()`? It simply calls the uclass
+method `bootdev_get_bootflow()` to ask the bootdev to return a bootflow. It
+passes the iterator to the bootdev method, so that function knows what we are
+talking about. At first, the bootflow is set up in the state `BOOTFLOWST_BASE`,
+with just the `method` and `dev` intiialised. But the bootdev may fill in more,
+e.g. updating the state, depending on what it finds.
+
+Based on what the bootdev responds with, `bootflow_check()` either
+returns a valid bootflow, or a partial one with an error. A partial bootflow
+is one that has some fields set up, but did not reach the `BOOTFLOWST_READY`
+state. As noted before, if the `BOOTFLOWF_ALL` iterator flag is set, then all
+bootflows are returned, even partial ones. This can help with debugging.
+
+So at this point you can see that total control over whether a bootflow can
+be generated from a particular iteration, or not, rests with the bootdev.
+Each one can adopt its own approach.
+
+Going down a level, what does the bootdev do in its `get_bootflow()` method?
+Let us consider the MMC bootdev. In that case the call to
+`bootdev_get_bootflow()` ends up in `mmc_get_bootflow()`. It locates the parent
+device of the bootdev, i.e. the `UCLASS_MMC` device itself, then finds the block
+device associated with it. It then calls the helper function
+`bootdev_find_in_blk()` to do all the work. This is common with just about any
+bootdev that is based on a media device.
+
+The `bootdev_find_in_blk()` helper is implemented in the bootdev uclass. It
+names the bootflow and copies the partition number in from the iterator. Then it
+calls the bootmeth device to check if it can support this device. This is
+important since some bootmeths only work with network devices, for example. If
+that check fails, it stops.
+
+Assuming the bootmeth is happy, or at least indicates that it is willing to try
+(by returning 0 from its `check()` method), the next step is to try the
+partition. If that works it tries to detect a file system. If that works then it
+calls the bootmeth device once more, this time to read the bootflow.
+
+Note: At present a filesystem is needed for the bootmeth to be called on block
+devices, simply because we don't have any examples where this is not the case.
+This feature can be added as needed.
+
+If we take the example of the `bootmeth_distro` driver, this call ends up at
+`distro_read_bootflow()`. It has the filesystem ready, so tries various
+filenames to try to find the `extlinux.conf` file, reading it if possible. If
+all goes well the bootflow ends up in the `BOOTFLOWST_READY` state.
+
+At this point, we fall back from the bootmeth driver, to
+`bootdev_find_in_blk()`, then back to `mmc_get_bootflow()`, then to
+`bootdev_get_bootflow()`, then to `bootflow_check()` and finally to its caller,
+either `bootflow_scan_bootdev()` or `bootflow_scan_next()`. In either case,
+the bootflow is returned as the result of this iteration, assuming it made it to
+the `BOOTFLOWST_READY` state.
+
+That is the basic operation of scanning for bootflows. The process of booting a
+bootflow is handled by the bootmeth driver for that bootflow. In the case of
+distro boot, this parses and processes the `extlinux.conf` file that was read.
+See `distro_boot()` for how that works. The processing may involve reading
+additional files, which is handled by the `read_file()` method, which is
+`distro_read_file()` in this case. All bootmethds should support reading files,
+since the bootflow is typically only the basic instructions and does not include
+the operating system itself, ramdisk, device tree, etc.
+
+The vast majority of the bootstd code is concerned with iterating through
+partitions on bootdevs and using bootmethds to find bootflows.
+
+How about bootdevs which are not block devices? They are handled by the same
+methods as above, but with a different implementation. For example, the bootmeth
+for PXE boot (over a network) uses `tftp` to read files rather than `fs_read()`.
+But other than that it is very similar.
+
+
+Tests
+-----
+
+Tests are located in `test/boot` and cover the core functionality as well as
+the commands. All tests use sandbox so can be run on a standard Linux computer
+and in U-Boot's CI.
+
+For testing, a DOS-formatted disk image is used with a single FAT partition on
+it. This is created in `setup_bootflow_image()`, with a canned one from the
+source tree used if it cannot be created (e.g. in CI).
+
+
+Bootflow internals
+------------------
+
+The bootstd device holds a linked list of scanned bootflows as well as the
+currently selected bootdev and bootflow (for use by commands). This is in
+`struct bootstd_priv`.
+
+Each bootdev device has its own `struct bootdev_uc_plat` which holds a
+list of scanned bootflows just for that device.
+
+The bootflow itself is documented in bootflow_h_. It includes various bits of
+information about the bootflow and a buffer to hold the file.
+
+
+Future
+------
+
+Apart from the to-do items below, different types of bootflow files may be
+implemented in future, e.g. Chromium OS support which is currently only
+available as a script in chromebook_coral.
+
+
+To do
+-----
+
+Some things that need to be done to completely replace the distro-boot scripts:
+
+- add bootdev drivers for dhcp, sata, scsi, ide, virtio
+- PXE boot for EFI
+- support for loading U-Boot scripts
+
+Other ideas:
+
+- `bootflow prep` to load everything preparing for boot, so that `bootflow boot`
+ can just do the boot.
+- automatically load kernel, FDT, etc. to suitable addresses so the board does
+ not need to specify things like `pxefile_addr_r`
+
+
+.. _disto_boodcmd: https://github.com/u-boot/u-boot/blob/master/include/config_distro_bootcmd.h
+.. _BootLoaderSpec: http://www.freedesktop.org/wiki/Specifications/BootLoaderSpec/
+.. _distro_boot: https://github.com/u-boot/u-boot/blob/master/boot/distro.c
+.. _bootflow_h: https://github.com/u-boot/u-boot/blob/master/include/bootflow.h
diff --git a/doc/develop/distro.rst b/doc/develop/distro.rst
index c522be6934..7ea84b5793 100644
--- a/doc/develop/distro.rst
+++ b/doc/develop/distro.rst
@@ -157,6 +157,9 @@ a line with "CONFIG_DISTRO_DEFAULTS=y". If you want to enable this
from Kconfig itself, for e.g. all boards using a specific SoC then
add a "imply DISTRO_DEFAULTS" to your SoC CONFIG option.

+
+TO BE UPDATED:
+
In your board configuration file, include the following::

#ifndef CONFIG_SPL_BUILD
diff --git a/doc/develop/index.rst b/doc/develop/index.rst
index 93ebfa485f..7c11fe4372 100644
--- a/doc/develop/index.rst
+++ b/doc/develop/index.rst
@@ -10,6 +10,7 @@ Implementation
:maxdepth: 1

bloblist
+ bootstd
ci_testing
commands
config_binding
diff --git a/doc/device-tree-bindings/bootdev.txt b/doc/device-tree-bindings/bootdev.txt
index 95b7fec821..4bb2345a0b 100644
--- a/doc/device-tree-bindings/bootdev.txt
+++ b/doc/device-tree-bindings/bootdev.txt
@@ -6,3 +6,21 @@ child of the media device (UCLASS_MMC, UCLASS_SPI_FLASH, etc.)

The bootdev driver is provided by the media devices. The bindings for each
are described in this file (to come).
+
+Required properties:
+
+compatible:
+ "u-boot,bootdev-eth" - Ethernet bootdev
+ "u-boot,bootdev-mmc" - MMC bootdev
+ "u-boot,bootdev-usb" - USB bootdev
+
+
+Example:
+
+ mmc1 {
+ compatible = "sandbox,mmc";
+
+ mmc-bootdev {
+ compatible = "u-boot,bootdev-eth";
+ };
+ };
diff --git a/doc/device-tree-bindings/bootmeth.txt b/doc/device-tree-bindings/bootmeth.txt
new file mode 100644
index 0000000000..de6396a7b3
--- /dev/null
+++ b/doc/device-tree-bindings/bootmeth.txt
@@ -0,0 +1,31 @@
+U-Boot standard boot methods (bootmeth)
+======================================
+
+This provides methods (called bootmeths) for locating bootflows on a boot
+device (bootdev). These are normally created as children of the bootstd device.
+
+Required properties:
+
+compatible:
+ "u-boot,distro-syslinux" - distro boot from a block device
+ "u-boot,distro-pxe" - distro boot from a network device
+ "u-boot,distro-efi" - EFI boot from an .efi file
+ "u-boot,efi-bootmgr" - EFI boot using boot manager (bootmgr)
+
+
+Example:
+
+ bootstd {
+ compatible = "u-boot,boot-std";
+
+ filename-prefixes = "/", "/boot/";
+ bootdev-order = "mmc2", "mmc1";
+
+ syslinux {
+ compatible = "u-boot,distro-syslinux";
+ };
+
+ efi {
+ compatible = "u-boot,distro-efi";
+ };
+ };
diff --git a/doc/device-tree-bindings/bootstd.txt b/doc/device-tree-bindings/bootstd.txt
index f048b9dd32..8706c5f499 100644
--- a/doc/device-tree-bindings/bootstd.txt
+++ b/doc/device-tree-bindings/bootstd.txt
@@ -25,4 +25,12 @@ Example:

filename-prefixes = "/", "/boot/";
bootdev-order = "mmc2", "mmc1";
+
+ syslinux {
+ compatible = "u-boot,distro-syslinux";
+ };
+
+ efi {
+ compatible = "u-boot,distro-efi";
+ };
};
diff --git a/doc/usage/bootdev.rst b/doc/usage/bootdev.rst
new file mode 100644
index 0000000000..ca5671e6f7
--- /dev/null
+++ b/doc/usage/bootdev.rst
@@ -0,0 +1,135 @@
+.. SPDX-License-Identifier: GPL-2.0+:
+
+bootdev command
+===============
+
+Synopis
+-------
+
+::
+
+ bootdev list [-p] - list all available bootdevs (-p to probe)\n"
+ bootdev select <bm> - select a bootdev by name\n"
+ bootdev info [-p] - show information about a bootdev";
+
+Description
+-----------
+
+The `bootdev` command is used to manage bootdevs. It can list available
+bootdevs, select one and obtain information about it.
+
+See :doc:`../develop/bootstd` for more information about bootdevs in general.
+
+
+bootdev list
+~~~~~~~~~~~~
+
+This lists available bootdevs
+
+Scanning with `-p` causes the bootdevs to be probed. This happens automatically
+when they are used.
+
+The list looks something like this:
+
+=== ====== ====== ======== =========================
+Seq Probed Status Uclass Name
+=== ====== ====== ======== =========================
+ 0 [ + ] OK mmc mmc@7e202000.bootdev
+ 1 [ ] OK mmc sdhci@7e300000.bootdev
+ 2 [ ] OK ethernet smsc95xx_eth.bootdev
+=== ====== ====== ======== =========================
+
+
+The fields are as follows:
+
+Seq:
+ Sequence number in the scan, used to reference the bootflow later
+
+Probed:
+ Shows a plus (+) if the device is probed, empty if not.
+
+Status:
+ Shows the status of the device. Typically this is `OK` meaning that there is
+ no error. If you use -p and an error occurs when probing, then this shows
+ the error number. You can look up Linux error codes to find the meaning of
+ the number.
+
+Uclass:
+ Name of the media device's Uclass. This indicates the type of the parent
+ device (e.g. MMC, Ethernet).
+
+Name:
+ Name of the bootdev. This is generated from the media device appended
+ with `.bootdev`
+
+
+bootdev select
+~~~~~~~~~~~~~~~~~
+
+Use this to select a particular bootdev. You can select it by the sequence
+number or name, as shown in `bootdev list`.
+
+Once a bootdev is selected, you can use `bootdev info` to look at it or
+`bootflow scan` to scan it.
+
+If no bootdev name or number is provided, then any existing bootdev is
+unselected.
+
+
+bootdev info
+~~~~~~~~~~~~~~~
+
+This shows information on the current bootdev, with the format looking like
+this:
+
+========= =======================
+Name mmc@7e202000.bootdev
+Sequence 0
+Status Probed
+Uclass mmc
+Bootflows 1 (1 valid)
+========= =======================
+
+Most of the information is the same as `bootdev list` above. The new fields
+are:
+
+Device
+ Name of the bootdev
+
+Status
+ Shows `Probed` if the device is probed, `OK` if not. If `-p` is used and the
+ device fails to probe, an error code is shown.
+
+Bootflows
+ Indicates the number of bootflows attached to the bootdev. This is 0
+ unless you have used 'bootflow scan' on the bootflow, or on all bootflows.
+
+
+Example
+-------
+
+This example shows listing available bootdev and getting information about
+one of them::
+
+ U-Boot> bootdev list
+ Seq Probed Status Uclass Name
+ --- ------ ------ -------- ------------------
+ 0 [ + ] OK mmc mmc@7e202000.bootdev
+ 1 [ ] OK mmc sdhci@7e300000.bootdev
+ 2 [ ] OK ethernet smsc95xx_eth.bootdev
+ --- ------ ------ -------- ------------------
+ (3 devices)
+ U-Boot> bootdev sel 0
+ U-Boot> bootflow scan
+ U-Boot> bootdev info
+ Name: mmc@7e202000.bootdev
+ Sequence: 0
+ Status: Probed
+ Uclass: mmc
+ Bootflows: 1 (1 valid)
+
+
+Return value
+------------
+
+The return value $? is always 0 (true).
diff --git a/doc/usage/bootflow.rst b/doc/usage/bootflow.rst
new file mode 100644
index 0000000000..347cc181bc
--- /dev/null
+++ b/doc/usage/bootflow.rst
@@ -0,0 +1,427 @@
+.. SPDX-License-Identifier: GPL-2.0+:
+
+bootflow command
+================
+
+Synopis
+-------
+
+::
+
+ bootflow scan [-abel] [bootdev]
+ bootflow list [-e]
+ bootflow select [<num|name>]
+ bootflow info [-d]
+ bootflow boot
+
+
+Description
+-----------
+
+The `bootflow` command is used to manage bootflows. It can scan bootdevs to
+locate bootflows, list them and boot them.
+
+See :doc:`../develop/bootstd` for more information.
+
+
+bootflow scan
+~~~~~~~~~~~~~
+
+Scans for available bootflows, optionally booting the first valid one it finds.
+This operates in two modes:
+
+- If no bootdev is selected (see `bootdev select`) it scans bootflows one
+ by one, extracting all the bootdevs from each
+- If a bootdev is selected, it just scans that one bootflow
+
+Flags are:
+
+-a
+ Collect all bootflows, even those that cannot be loaded. Normally if a file
+ is not where it is expected, then the bootflow fails and so is dropped
+ during the scan. With this option you can see why each bootflow would be
+ dropped.
+
+-b
+ Boot each valid bootflow as it is scanned. Typically only the first bootflow
+ matters, since by then the system boots in the OS and U-Boot is no-longer
+ running. `bootflow scan -b` is a quick way to boot the first available OS.
+ A valid bootflow is one that made it all the way to the `loaded` state.
+
+-e
+ Used with -l to also show errors for each bootflow. The shows detailed error
+ information for each bootflow that failed to make it to the `loaded` state.
+
+-l
+ List bootflows while scanning. This is helpful when you want to see what
+ is happening during scanning. Use it with the `-b` flag to see which
+ bootdev and bootflows are being tried.
+
+The optional argument specifies a particular bootdev to scan. This can either be
+the name of a bootdev or its sequence number (both shown with `bootdev list`).
+Alternatively a convenience label can be used, like `mmc0`, which is the type of
+device and an optional sequence number. Specifically, the label is the uclass of
+the bootdev's parent followed by the sequence number of that parent. Sequence
+numbers are typically set by aliases, so if you have 'mmc0' in your devicetree
+alias section, then `mmc0` refers to the bootdev attached to that device.
+
+
+bootflow list
+~~~~~~~~~~~~~
+
+Lists the previously scanned bootflows. You must use `bootflow scan` before this
+to see anything.
+
+If you scanned with -a and have bootflows with errors, -e can be used to show
+those errors.
+
+The list looks something like this:
+
+=== ====== ====== ======== ==== =============================== ================
+Seq Method State Uclass Part Name Filename
+=== ====== ====== ======== ==== =============================== ================
+ 0 distro ready mmc 2 mmc\@7e202000.bootdev.part_2 /boot/extlinux/extlinux.conf
+ 1 pxe ready ethernet 0 smsc95xx_eth.bootdev.0 rpi.pxe/extlinux/extlinux.conf
+=== ====== ====== ======== ==== =============================== ================
+
+The fields are as follows:
+
+Seq:
+ Sequence number in the scan, used to reference the bootflow later
+
+Method:
+ The boot method (bootmeth) used to find the bootflow. Several methods are
+ included in U-Boot.
+
+State:
+ Current state of the bootflow, indicating how far the bootdev got in
+ obtaining a valid one. See :ref:`BootflowStates` for a list of states.
+
+Uclass:
+ Name of the media device's Uclass. This indicates the type of the parent
+ device (e.g. MMC, Ethernet).
+
+Part:
+ Partition number being accesseed, numbered from 1. Normally a device will
+ have a partition table with a small number of partitions. For devices
+ without partition tables (e.g. network) this field is 0.
+
+Name:
+ Name of the bootflow. This is generated from the bootdev appended with
+ the partition information
+
+Filename:
+ Name of the bootflow file. This indicates where the file is on the
+ filesystem or network device.
+
+
+bootflow select
+~~~~~~~~~~~~~~~
+
+Use this to select a particular bootflow. You can select it by the sequence
+number or name, as shown in `bootflow list`.
+
+Once a bootflow is selected, you can use `bootflow info` and `bootflow boot`.
+
+If no bootflow name or number is provided, then any existing bootflow is
+unselected.
+
+
+bootflow info
+~~~~~~~~~~~~~
+
+This shows information on the current bootflow, with the format looking like
+this:
+
+========= ===============================
+Name mmc\@7e202000.bootdev.part_2
+Device mmc\@7e202000.bootdev
+Block dev mmc\@7e202000.blk
+Type distro
+Method: syslinux
+State ready
+Partition 2
+Subdir (none)
+Filename /extlinux/extlinux.conf
+Buffer 3db7ad48
+Size 232 (562 bytes)
+Error 0
+========= ===============================
+
+Most of the information is the same as `bootflow list` above. The new fields
+are:
+
+Device
+ Name of the bootdev
+
+Block dev
+ Name of the block device, if any. Network devices don't have a block device.
+
+Subdir
+ Subdirectory used for retrieving files. For network bootdevs this is the
+ directory of the 'bootfile' parameter passed from DHCP. All file retrievals
+ when booting are relative to this.
+
+Buffer
+ Buffer containing the bootflow file. You can use the :doc:`md` to look at
+ it, or dump it with `bootflow info -d`.
+
+Size
+ Size of the bootflow file
+
+Error
+ Error number returned from scanning for the bootflow. This is 0 if the
+ bootflow is in the 'loaded' state, or a negative error value on error. You
+ can look up Linux error codes to find the meaning of the number.
+
+Use the `-d` flag to dump out the contents of the bootfile file.
+
+
+bootflow boot
+~~~~~~~~~~~~~
+
+This boots the current bootflow.
+
+
+Example
+-------
+
+Here is an example of scanning for bootflows, then listing them::
+
+ U-Boot> bootflow scan -l
+ Scanning for bootflows in all bootdevs
+ Seq Type State Uclass Part Name Filename
+ --- ----------- ------ -------- ---- ------------------------ ----------------
+ Scanning bootdev 'mmc@7e202000.bootdev':
+ 0 distro ready mmc 2 mmc@7e202000.bootdev.p /extlinux/extlinux.conf
+ Scanning bootdev 'sdhci@7e300000.bootdev':
+ Card did not respond to voltage select! : -110
+ Scanning bootdev 'smsc95xx_eth.bootdev':
+ Waiting for Ethernet connection... done.
+ BOOTP broadcast 1
+ DHCP client bound to address 192.168.4.30 (4 ms)
+ Using smsc95xx_eth device
+ TFTP from server 192.168.4.1; our IP address is 192.168.4.30
+ Filename 'rpi.pxe/'.
+ Load address: 0x200000
+ Loading: *
+ TFTP error: 'Is a directory' (0)
+ Starting again
+
+ missing environment variable: pxeuuid
+ Retrieving file: rpi.pxe/pxelinux.cfg/01-b8-27-eb-a6-61-e1
+ Waiting for Ethernet connection... done.
+ Using smsc95xx_eth device
+ TFTP from server 192.168.4.1; our IP address is 192.168.4.30
+ Filename 'rpi.pxe/pxelinux.cfg/01-b8-27-eb-a6-61-e1'.
+ Load address: 0x2500000
+ Loading: ################################################## 566 Bytes
+ 45.9 KiB/s
+ done
+ Bytes transferred = 566 (236 hex)
+ 1 distro ready ethernet 0 smsc95xx_eth.bootdev.0 rpi.pxe/extlinux/extlinux.conf
+ No more bootdevs
+ --- ----------- ------ -------- ---- ------------------------ ----------------
+ (2 bootflows, 2 valid)
+ U-Boot> bootflow l
+ Showing all bootflows
+ Seq Type State Uclass Part Name Filename
+ --- ----------- ------ -------- ---- ------------------------ ----------------
+ 0 distro ready mmc 2 mmc@7e202000.bootdev.p /extlinux/extlinux.conf
+ 1 pxe ready ethernet 0 smsc95xx_eth.bootdev.0 rpi.pxe/extlinux/extlinux.conf
+ --- ----------- ------ -------- ---- ------------------------ ----------------
+ (2 bootflows, 2 valid)
+
+
+The second one is then selected by name (we could instead use `bootflow sel 0`),
+displayed and booted::
+
+ U-Boot> bootflow info
+ No bootflow selected
+ U-Boot> bootflow sel mmc@7e202000.bootdev.part_2
+ U-Boot> bootflow info
+ Name: mmc@7e202000.bootdev.part_2
+ Device: mmc@7e202000.bootdev
+ Block dev: mmc@7e202000.blk
+ Sequence: 1
+ Method: distro
+ State: ready
+ Partition: 2
+ Subdir: (none)
+ Filename: extlinux/extlinux.conf
+ Buffer: 3db7ae88
+ Size: 232 (562 bytes)
+ Error: 0
+ U-Boot> bootflow boot
+ ** Booting bootflow 'smsc95xx_eth.bootdev.0'
+ Ignoring unknown command: ui
+ Ignoring malformed menu command: autoboot
+ Ignoring malformed menu command: hidden
+ Ignoring unknown command: totaltimeout
+ 1: Fedora-Workstation-armhfp-31-1.9 (5.3.7-301.fc31.armv7hl)
+ Retrieving file: rpi.pxe/initramfs-5.3.7-301.fc31.armv7hl.img
+ get 2700000 rpi.pxe/initramfs-5.3.7-301.fc31.armv7hl.img
+ Waiting for Ethernet connection... done.
+ Using smsc95xx_eth device
+ TFTP from server 192.168.4.1; our IP address is 192.168.4.30
+ Filename 'rpi.pxe/initramfs-5.3.7-301.fc31.armv7hl.img'.
+ Load address: 0x2700000
+ Loading: ###################################T ############### 57.7 MiB
+ 1.9 MiB/s
+ done
+ Bytes transferred = 60498594 (39b22a2 hex)
+ Retrieving file: rpi.pxe//vmlinuz-5.3.7-301.fc31.armv7hl
+ get 80000 rpi.pxe//vmlinuz-5.3.7-301.fc31.armv7hl
+ Waiting for Ethernet connection... done.
+ Using smsc95xx_eth device
+ TFTP from server 192.168.4.1; our IP address is 192.168.4.30
+ Filename 'rpi.pxe//vmlinuz-5.3.7-301.fc31.armv7hl'.
+ Load address: 0x80000
+ Loading: ################################################## 7.2 MiB
+ 2.3 MiB/s
+ done
+ Bytes transferred = 7508480 (729200 hex)
+ append: ro root=UUID=9732b35b-4cd5-458b-9b91-80f7047e0b8a rhgb quiet LANG=en_US.UTF-8 cma=192MB cma=256MB
+ Retrieving file: rpi.pxe//dtb-5.3.7-301.fc31.armv7hl/bcm2837-rpi-3-b.dtb
+ get 2600000 rpi.pxe//dtb-5.3.7-301.fc31.armv7hl/bcm2837-rpi-3-b.dtb
+ Waiting for Ethernet connection... done.
+ Using smsc95xx_eth device
+ TFTP from server 192.168.4.1; our IP address is 192.168.4.30
+ Filename 'rpi.pxe//dtb-5.3.7-301.fc31.armv7hl/bcm2837-rpi-3-b.dtb'.
+ Load address: 0x2600000
+ Loading: ################################################## 13.8 KiB
+ 764.6 KiB/s
+ done
+ Bytes transferred = 14102 (3716 hex)
+ Kernel image @ 0x080000 [ 0x000000 - 0x729200 ]
+ ## Flattened Device Tree blob at 02600000
+ Booting using the fdt blob at 0x2600000
+ Using Device Tree in place at 02600000, end 02606715
+
+ Starting kernel ...
+
+ [ OK ] Started Show Plymouth Boot Screen.
+ [ OK ] Started Forward Password R…s to Plymouth Directory Watch.
+ [ OK ] Reached target Local Encrypted Volumes.
+ [ OK ] Reached target Paths.
+ ....
+
+
+Here we scan for bootflows and boot the first one found::
+
+ U-Boot> bootflow scan -bl
+ Scanning for bootflows in all bootdevs
+ Seq Method State Uclass Part Name Filename
+ --- ----------- ------ -------- ---- ---------------------- ----------------
+ Scanning bootdev 'mmc@7e202000.bootdev':
+ 0 distro ready mmc 2 mmc@7e202000.bootdev.p /extlinux/extlinux.conf
+ ** Booting bootflow 'mmc@7e202000.bootdev.part_2'
+ Ignoring unknown command: ui
+ Ignoring malformed menu command: autoboot
+ Ignoring malformed menu command: hidden
+ Ignoring unknown command: totaltimeout
+ 1: Fedora-KDE-armhfp-31-1.9 (5.3.7-301.fc31.armv7hl)
+ Retrieving file: /initramfs-5.3.7-301.fc31.armv7hl.img
+ getfile 2700000 /initramfs-5.3.7-301.fc31.armv7hl.img
+ Retrieving file: /vmlinuz-5.3.7-301.fc31.armv7hl
+ getfile 80000 /vmlinuz-5.3.7-301.fc31.armv7hl
+ append: ro root=UUID=b8781f09-e2dd-4cb8-979b-7df5eeaaabea rhgb LANG=en_US.UTF-8 cma=192MB console=tty0 console=ttyS1,115200
+ Retrieving file: /dtb-5.3.7-301.fc31.armv7hl/bcm2837-rpi-3-b.dtb
+ getfile 2600000 /dtb-5.3.7-301.fc31.armv7hl/bcm2837-rpi-3-b.dtb
+ Kernel image @ 0x080000 [ 0x000000 - 0x729200 ]
+ ## Flattened Device Tree blob at 02600000
+ Booting using the fdt blob at 0x2600000
+ Using Device Tree in place at 02600000, end 02606715
+
+ Starting kernel ...
+
+ [ 0.000000] Booting Linux on physical CPU 0x0
+
+
+Here is am example using the -e flag to see all errors::
+
+ U-Boot> bootflow scan -a
+ Card did not respond to voltage select! : -110
+ Waiting for Ethernet connection... done.
+ BOOTP broadcast 1
+ DHCP client bound to address 192.168.4.30 (4 ms)
+ Using smsc95xx_eth device
+ TFTP from server 192.168.4.1; our IP address is 192.168.4.30
+ Filename 'rpi.pxe/'.
+ Load address: 0x200000
+ Loading: *
+ TFTP error: 'Is a directory' (0)
+ Starting again
+
+ missing environment variable: pxeuuid
+ Retrieving file: rpi.pxe/pxelinux.cfg/01-b8-27-eb-a6-61-e1
+ Waiting for Ethernet connection... done.
+ Using smsc95xx_eth device
+ TFTP from server 192.168.4.1; our IP address is 192.168.4.30
+ Filename 'rpi.pxe/pxelinux.cfg/01-b8-27-eb-a6-61-e1'.
+ Load address: 0x2500000
+ Loading: ################################################## 566 Bytes
+ 49.8 KiB/s
+ done
+ Bytes transferred = 566 (236 hex)
+ U-Boot> bootflow l -e
+ Showing all bootflows
+ Seq Type State Uclass Part Name Filename
+ --- ----------- ------ -------- ---- --------------------- ----------------
+ 0 distro fs mmc 1 mmc@7e202000.bootdev.p /extlinux/extlinux.conf
+ ** File not found, err=-2
+ 1 distro ready mmc 2 mmc@7e202000.bootdev.p /extlinux/extlinux.conf
+ 2 distro fs mmc 3 mmc@7e202000.bootdev.p /extlinux/extlinux.conf
+ ** File not found, err=-1
+ 3 distro media mmc 0 mmc@7e202000.bootdev.p <NULL>
+ ** No partition found, err=-2
+ 4 distro media mmc 0 mmc@7e202000.bootdev.p <NULL>
+ ** No partition found, err=-2
+ 5 distro media mmc 0 mmc@7e202000.bootdev.p <NULL>
+ ** No partition found, err=-2
+ 6 distro media mmc 0 mmc@7e202000.bootdev.p <NULL>
+ ** No partition found, err=-2
+ 7 distro media mmc 0 mmc@7e202000.bootdev.p <NULL>
+ ** No partition found, err=-2
+ 8 distro media mmc 0 mmc@7e202000.bootdev.p <NULL>
+ ** No partition found, err=-2
+ 9 distro media mmc 0 mmc@7e202000.bootdev.p <NULL>
+ ** No partition found, err=-2
+ a distro media mmc 0 mmc@7e202000.bootdev.p <NULL>
+ ** No partition found, err=-2
+ b distro media mmc 0 mmc@7e202000.bootdev.p <NULL>
+ ** No partition found, err=-2
+ c distro media mmc 0 mmc@7e202000.bootdev.p <NULL>
+ ** No partition found, err=-2
+ d distro media mmc 0 mmc@7e202000.bootdev.p <NULL>
+ ** No partition found, err=-2
+ e distro media mmc 0 mmc@7e202000.bootdev.p <NULL>
+ ** No partition found, err=-2
+ f distro media mmc 0 mmc@7e202000.bootdev.p <NULL>
+ ** No partition found, err=-2
+ 10 distro media mmc 0 mmc@7e202000.bootdev.p <NULL>
+ ** No partition found, err=-2
+ 11 distro media mmc 0 mmc@7e202000.bootdev.p <NULL>
+ ** No partition found, err=-2
+ 12 distro media mmc 0 mmc@7e202000.bootdev.p <NULL>
+ ** No partition found, err=-2
+ 13 distro media mmc 0 mmc@7e202000.bootdev.p <NULL>
+ ** No partition found, err=-2
+ 14 distro ready ethernet 0 smsc95xx_eth.bootdev.0 rpi.pxe/extlinux/extlinux.conf
+ --- ----------- ------ -------- ---- --------------------- ----------------
+ (21 bootflows, 2 valid)
+ U-Boot>
+
+
+Return value
+------------
+
+On success `bootflow boot` normally boots into the Operating System and does not
+return to U-Boot. If something about the U-Boot processing fails, then the
+return value $? is 1. If the boot succeeds but for some reason the Operating
+System returns, then $? is 0, indicating success.
+
+For other subcommands, the return value $? is always 0 (true).
+
+
+.. BootflowStates_:
diff --git a/doc/usage/bootmeth.rst b/doc/usage/bootmeth.rst
new file mode 100644
index 0000000000..bba37c6a40
--- /dev/null
+++ b/doc/usage/bootmeth.rst
@@ -0,0 +1,108 @@
+.. SPDX-License-Identifier: GPL-2.0+:
+
+bootmeth command
+================
+
+Synopis
+-------
+
+::
+
+ bootmeth list [-a] - list selected bootmeths (-a for all)
+ bootmeth order "[<bm> ...]" - select the order of bootmeths\n"
+
+
+Description
+-----------
+
+The `bootmeth` command is used to manage bootmeths. It can list them and change
+the order in which they are used.
+
+See :doc:`../develop/bootstd` for more information.
+
+
+.. _bootmeth_order:
+
+bootmeth order
+~~~~~~~~~~~~~~
+
+Selects which bootmeths to use and the order in which they are invoked. When
+scanning bootdevs, each bootmeth is tried in turn to see if it can find a valid
+bootflow. You can use this command to adjust the order or even to omit some
+boomeths.
+
+The argument is a quoted list of bootmeths to use, by name.
+
+
+bootmeth list
+~~~~~~~~~~~~~
+
+This lists the selected bootmeths, or all of them, if the `-a` flag is used.
+The format looks like this:
+
+===== === ================== =================================
+Order Seq Name Description
+===== === ================== =================================
+ 0 0 distro Syslinux boot from a block device
+ 1 1 efi EFI boot from an .efi file
+ 2 2 pxe PXE boot from a network device
+ 3 3 sandbox Sandbox boot for testing
+ 4 4 efi_mgr EFI bootmgr flow
+===== === ================== =================================
+
+The fields are as follows:
+
+Order:
+ The order in which these bootmeths are invoked for each bootdev. If this
+ shows as a hyphen, then the bootmeth is not in the current ordering.
+
+Seq:
+ The sequence number of the bootmeth, i.e. the normal ordering if none is set
+
+Name:
+ Name of the bootmeth
+
+Description:
+ A friendly description for the bootmeth
+
+
+Example
+-------
+
+This shows listing bootmeths. All are present and in the normal order::
+
+ => bootmeth list
+ Order Seq Name Description
+ ----- --- ------------------ ------------------
+ 0 0 distro Syslinux boot from a block device
+ 1 1 efi EFI boot from an .efi file
+ 2 2 pxe PXE boot from a network device
+ 3 3 sandbox Sandbox boot for testing
+ 4 4 efi_mgr EFI bootmgr flow
+ ----- --- ------------------ ------------------
+ (5 bootmeths)
+
+Now the order is changed, to include only two of them::
+
+ => bootmeth order "sandbox distro"
+ => bootmeth list
+ Order Seq Name Description
+ ----- --- ------------------ ------------------
+ 0 3 sandbox Sandbox boot for testing
+ 1 0 distro Syslinux boot from a block device
+ ----- --- ------------------ ------------------
+ (2 bootmeths)
+
+The -a flag shows all bootmeths so you can clearly see which ones are used and
+which are not::
+
+ => bootmeth list -a
+ Order Seq Name Description
+ ----- --- ------------------ ------------------
+ 1 0 distro Syslinux boot from a block device
+ - 1 efi EFI boot from an .efi file
+ - 2 pxe PXE boot from a network device
+ 0 3 sandbox Sandbox boot for testing
+ - 4 efi_mgr EFI bootmgr flow
+ ----- --- ------------------ ------------------
+ (5 bootmeths)
diff --git a/doc/usage/index.rst b/doc/usage/index.rst
index 0aacf531b2..5baf5df18a 100644
--- a/doc/usage/index.rst
+++ b/doc/usage/index.rst
@@ -22,9 +22,12 @@ Shell commands
addrmap
askenv
base
+ bootdev
bootefi
+ bootflow
booti
bootmenu
+ bootmeth
button
x86/cbsysinfo
conitrace
--
2.35.1.616.g0bdcbb4464-goog