Extending `zephyr,code-partition` with `zephyr,code-header-size`

[Laczen]

Is your enhancement proposal related to a problem? Please describe.

At the moment it is possible to generate images for a specific partition by using zephyr,code-partition = &partition in the dts.

However it is not possible to specify the size of the header. This is specified by e.g. selecting CONFIG_USE_MCUBOOT = y.

If it would be possible to specify the header size in the dts by using (e.g. zephyr,code-header-size = <0x200> the generation of images for any bootloader would be simplified by creating an appropriate overlay.

The zephyr default that does not specify zephyr,code-partition or zephyr,code-header-size would generate an image for the complete flash0.

A dts that specifies zephyr,code-partition but not zephyr,code-header-size would generate a image for code-partition starting at the start of the partition. Using a dts that specifies an image partition and a storage partition would avoid that the image overflows in the storage partition. This could be the default dts for boards that are using the storage area.

A dts that specifies zephyr, code-partition and zephyr,code-header-size would generate a image for code-partition but starting after the code-header-size. This could be specified in a mcuboot dts that includes (redefines) partitioning and redefines zephyr,code-partition and sets zephyr,code-header-size = <0x200>.

Describe alternatives you've considered
Alternative solutions have been proposed in #27974 and #31073 (side benefit).

[de-nordic]

What about CONFIG_ROM_START_OFFSET ? If the CONFIG_USE_MCUBOOT is not set this value defaults to 0 and is configurable.

[Laczen]

@de-nordic, thanks for the feedback.

The idea is to remove everything from Kconfig, only use dts (and overlays). CONFIG_ROM_START_OFFSET would be calculated from zephyr,code-header-size (if set).

[de-nordic]

I'm not sure, but this #29794 (review) may apply here.

The idea is to remove everything from Kconfig, only use dts (and overlays).

I am in favour of the idea, but for everything that can be considered hardware parameters.
The problem with zephyr,code-header-size is that this is actually software parameter rather than something that applies to hardware configuration. I am not sure about this.

[Laczen]

@de-nordic, I think this could be considered a hardware parameter, it is something that the "hardware" (bootloader) expects, it is not related to the image (software) itself. But in this case the line is difficult to draw.

@galak, what is your opinion on the proposal ? It is true that it could be considered a software parameter, but it might be the simplest way to support whatever bootloader and to resolve #27471.

[Laczen]

@ioannisg, fyi

[Laczen]

@mbolivar-nordic, what is your opinion on the proposal ?

[Laczen]

I am closing this as there is an alternative proposal.