fastboot: introduce 'oem board' subcommand

Currently, fastboot protocol in U-Boot has no opportunity
to execute vendor custom code with verifed boot. This patch
introduce new fastboot subcommand fastboot oem board:<cmd>,
which allow to run custom oem_board function.

Default implementation is __weak. Vendor must redefine it in
board/ folder with his own logic.

For example, some vendors have their custom nand/emmc partition
flashing or erasing. Here some typical command for such use cases:

- flashing:

  $ fastboot stage bootloader.img
  $ fastboot oem board:write_bootloader

- erasing:

  $ fastboot oem board:erase_env

Signed-off-by: Alexey Romanov <avromanov@salutedevices.com>
Reviewed-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>
Reviewed-by: Quentin Schulz <quentin.schulz@theobroma-systems.com>
Link: https://lore.kernel.org/r/20240418100129.1691822-2-avromanov@salutedevices.com
Signed-off-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>

1 files changed, 18 insertions, 0 deletions

diff --git a/doc/android/fastboot.rst b/doc/android/fastboot.rst
index 9e337cae2cb..1a60968bb17 100644
--- a/doc/android/fastboot.rst
+++ b/doc/android/fastboot.rst
@@ -30,6 +30,7 @@ The following OEM commands are supported (if enabled):
 - ``oem bootbus``  - this executes ``mmc bootbus %x %s`` to configure eMMC
 - ``oem run`` - this executes an arbitrary U-Boot command
 - ``oem console`` - this dumps U-Boot console record buffer
+- ``oem board`` - this executes a custom board function which is defined by the vendor
 
 Support for both eMMC and NAND devices is included.
 
@@ -247,6 +248,23 @@ including multiple commands (using e.g. ``;`` or ``&&``) and control structures
 (``if``, ``while``, etc.). The exit code of ``fastboot`` will reflect the exit
 code of the command you ran.
 
+Running Custom Vendor Code
+^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+U-Boot allows you to execute custom fastboot logic, which can be defined
+in board/ files. It can still be used for production devices with verified
+boot, because the vendor defines logic at compile time by implementing
+fastboot_oem_board() function. The attacker will not be able to execute
+custom commands / code. For example, this can be useful for custom flashing
+or erasing protocols::
+
+    $ fastboot stage bootloader.img
+    $ fastboot oem board:write_bootloader
+
+In this case, ``cmd_parameter`` argument of the function ``fastboot_oem_board()``
+will contain string "write_bootloader" and ``data`` argument is a pointer to
+fastboot input buffer, which contains the contents of bootloader.img file.
+
 References
 ----------