[PATCH 1/2] Documentation: boards: stm32mp: document USB bootstrap via DFU

[Ahmad Fatoum <a.fatoum@pengutronix.de>]

TF-A v2.6 now supports DFU for USB bootstrap on the STM32MP1. This is
normally exercised by the STM32CubeProgrammer, but is easily usable with
just dfu-util as well. Document how to.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
---
 Documentation/boards/stm32mp.rst | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/Documentation/boards/stm32mp.rst b/Documentation/boards/stm32mp.rst
index 0c9615b290a5..4cdd281a9e14 100644
--- a/Documentation/boards/stm32mp.rst
+++ b/Documentation/boards/stm32mp.rst
@@ -49,6 +49,8 @@ In the above output, images with a ``.stm32`` extension feature the (legacy)
 stm32image header. ``barebox-dt-2nd.img`` and ``barebox-stm32mp-generic-bl33.img``
 are board-generic barebox images that receive an external device tree.
 
+.. _stm32mp_fip:
+
 Flashing barebox (FIP)
 ----------------------
 
@@ -137,6 +139,34 @@ Assuming ``CONFIG_CMD_MMC_EXTCSD`` is enabled and the board shall boot from
 The STM32MP1 BootROM does *not* support booting from eMMC without fast boot
 acknowledge.
 
+USB Bootstrap (DFU)
+-------------------
+
+The STM32MP1 can be strapped to boot from USB. After Power-On reset, it
+should be detectable as ``STMicroelectronics STM Device in DFU Mode``
+and can be uploaded to with ``dfu-util(1)``::
+
+  dfu-util --alt 1 -D tf-a-stm32mp157c-my-board.stm32
+  dfu-util --alt 3 -D bl3-firmware.fip
+  dfu-util --alt 0 -e
+
+The first command will talk to the BootROM and upload the first stage
+bootloader (ARM Trusted Firmware-A) into on-chip SRAM.
+
+When compiled with ``STM32MP_USB_PROGRAMMER=1``, TF-A v2.6 or higher
+will seamlessly continue operation of the DFU gadget. The second
+command will talk to TF-A to upload a Firmware Image Package, which
+is a format bundling further firmware including barebox.
+
+The final command will instruct TF-A to boot the loaded images.
+This all happens in volatile memory. To persist images, use
+normal barebox functionality like creating a DFU-gadget in barebox,
+Fastboot/USB mass storage ... etc.
+
+The FIP image containing barebox can be generated as described in
+137::ref:`stm32mp_fip`. Upstream TF-A doesn't support DFU for
+SSBLs using the legacy stm32image format.
+
 Boot source selection
 ---------------------
 
-- 
2.30.2


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