Sysbuild linker flash size requires manual config

[vChavezB]

I have started to test Sysbuild to build mcuboot for my application.

Even though I have defined for my board the partitions such as

&flash0 {

	partitions {
		compatible = "fixed-partitions";
		#address-cells = <1>;
		#size-cells = <1>;

		boot_partition: partition@0 {
			label = "mcuboot";
			reg = <0x00000000 DT_SIZE_K(48)>;
			read-only;
		};
		slot0_partition: partition@c000 {
			label = "image-0";
			reg = <0x0000c000 DT_SIZE_K(224)>;
		};
	};
};

These values are not taken into account for the final build with the linker script.
Instead the linker script for both images (mcuboot and application) uses the complete flash size (256 KB). This is counterintuitive as when building the bootloader and the app I want to know if the images will fit.

After some digging in the CMake for the linker generator (linker.cmd) I came up with manually defining CONFIG_FLASH_SIZE for both images.

Is this the correct way to do this or am I missing something to make Zephyr automatically define CONFIG_FLASH_SIZE based on the partitions I defined ?

[vChavezB]

After some more digging I found that I had to set CONFIG_USE_DT_CODE_PARTITION=y for zephyr to use the correct flash settings and size for building the main app.

In addition for my mcuboot partition I had to add an overlay to specifiy the boot partition as the code partition.

/ {
	chosen {
		zephyr,code-partition = &boot_partition;
	};
};

Just curious, is this mentioned in the sys build https://github.com/zephyrproject-rtos/zephyr/blob/main/doc/build/sysbuild/index.rst ?

I Had to invest some time to learn this. As far as I know the sys build samples do not have this code. Just found a reference to this in the code for tests.