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[RFC] Support image sources other than flash #2031

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[RFC] Support image sources other than flash #2031

wants to merge 4 commits into from

Commits on Aug 8, 2024

  1. boot/bootutil: Split RAM load code to its own file 

    RAM loading code is currently under bootutil/loader.c, and it's not
accessible for different loaders, such as the single loaders. Future
patches will make use of the RAM loading code outside the
bootutil/loader.c context, and this patch prepares for that by making it
standalone on boot/bootutil/src/ram_load.c

Signed-off-by: Ederson de Souza <[email protected]>
    @edersondisouza
    edersondisouza committed Aug 8, 2024
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  2. boot/zephyr: Move RAM load Kconfigs outside !SINGLE_APPLICATION_SLOT 

    Now that RAM load code is not dependent on bootutil/loader.c, it can be
used independently of !SINGLE_APPLICATION_SLOT configurations. Move the
related Kconfigs accordingly, so that applications configured to use
single loader can do RAM loading.

Signed-off-by: Ederson de Souza <[email protected]>
    @edersondisouza
    edersondisouza committed Aug 8, 2024
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  3. boot/zephyr: Support image sources other than flash 

    MCUboot assumes that the images being booted live on a flash (or will be
loaded to it, in case of serial support). However, some devices may end
up loading an image from a different source, such as an I2C/eSPI storage,
using some appropriate protocol. In these cases, usually the image is
then loaded directly to RAM.

This patch adds support for such scenarios, currently only on Zephyr
port. It expects Zephyr CONFIG_FLASH_MAP_CUSTOM_BACKEND is used to
provide Flash Map API to access the image in the non-flash device (but
doesn't mandate it). This allows for an integration that is less intrusive
on MCUboot code.

It uses single loader to load an image from a set of "sources". The
single loader loops through available sources and the first one to
succeed signature/validation boots. To access the images, weak functions
flash_map_id_get_next() and flash_map_id_get_current() are used. Default
implementation keeps current behaviour for single loader, i.e. just
loads from FLASH_AREA_IMAGE_PRIMARY(0).

It is expected applications will reimplement these functions, allowing
them to define a priority of different sources. As these different
storage media may be ready only, MCUboot won't attempt to update them to
record last source to succeed or so, it's application responsibility to
define the correct priority of sources on every boot.

Signed-off-by: Ederson de Souza <[email protected]>
    @edersondisouza
    edersondisouza committed Aug 8, 2024
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  4. samples: Add a sample for non-flash-source 

    A sample for non-flash-source on MEC17 EVB. It provides implementation
for Zephyr flash_area_open_custom(), so the right flash map
implementation is used, and MCUboot flash_map_id_get_next() and
flash_map_id_get_current() to prioritize sources. It should show what is
expected from an application to be able to use non-flash sources for
images.

For the I2C device simulation, an Aardvark I2C host adapter is needed,
and a script is provided to make the image loadable via I2C. An
implementation for an "Aardvark driver" on top of I2C is also provided.
Finally, a sample application to be loaded is also available.

For more details on how to build and test the samples, check the
provided README.md.

Signed-off-by: Ederson de Souza <[email protected]>
    @edersondisouza
    edersondisouza committed Aug 8, 2024
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