Merge tag 'efi-2021-10-rc2-2' of https://source.denx.de/u-boot/custodians/u-boot-efi

Pull request for efi-2021-10-rc2-2

Documentation:

* Require Sphinx >= 2.4.4 for 'make htmldocs'
* Move devicetree documentation to restructured text and update it
* Document stm32mp1 devicetree bindings

UEFI

* Extend measurement to UEFI variables and ExitBootServices()
* Support Uri() node in devicetree to text protocol
* Add Linux magic token to RISC-V EFI test binaries

1 files changed, 44 insertions, 0 deletions

diff --git a/doc/develop/devicetree/intro.rst b/doc/develop/devicetree/intro.rst
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+.. SPDX-License-Identifier: GPL-2.0+
+
+Devicetree Introduction
+=======================
+
+U-Boot uses a devicetree for configuration. This includes the devices used by
+the board, the format of the image created with binman, which UART to use for
+the console, public keys used for secure boot and many other things.
+
+See :doc:`control` for more information.
+
+Why does U-Boot put <thing> in the devicetree?
+----------------------------------------------
+
+This question comes up a lot with people new to U-Boot, particular those coming
+from Linux who are used to quite strict rules about what can go into the
+devicetree.
+
+U-Boot uses the same devicetree as Linux but adds more things necessary for the
+bootloader environment (see :ref:`dttweaks`).
+
+U-Boot does not have a user space to provide policy and configuration. It cannot
+do what Linux does and run programs and look up filesystems to figure out how to
+boot. So configuration and runtime information goes into the devicetree in
+U-Boot.
+
+Of course it is possible to:
+
+- add tables into the rodata section of the U-Boot binary
+- append some info to the end of U-Boot in a different format
+- modify the linker script to bring in a file with some info in it
+- put things in ACPI tables
+- link in a UEFI hand-off block structure and put things in there
+
+but *please don't*. In general, devicetree is the sane place to hold U-Boot's
+configuration.
+
+So, please, do NOT ask why U-Boot puts <thing> in the devicetree. It is the only
+place it can go. It is a highly suitable data structure for just about anything
+that U-Boot needs to know at runtime.
+
+Note, it is possible to use platdata directly so drivers avoid devicetreee in
+SPL. But of-platdata is the modern way of avoiding devicetree overhead, so
+please use that instead.