scripts: list_boards: add fast path for --board flag

[gudnimg]

Summary

• Speed up the execution time of find_v2_boards() if the board name is already known and avoid call to rglob. This change both reduces memory used and also IO activity on the file system.
• 85acca8 Fixes an issue when using the new fast path. The folder path should contain a valid board name, especially when it is being extended with new variants. If boards/native/native_sim/board.yml is being extended, the folder path for the new variants should be the same, and not boards/native/native_sim_extend/board.yml. In other words, the <board> name should match.

Comparison

On my machine I see the execution time drop from ~1.6 seconds to ~0.5 seconds. In my screenshots below 1.506 seconds drops to 0.556 seconds. When sysbuild is enabled, the time savings are doubled because this process is executed twice.

My machine uses AMD Ryzen 5800X3D, 32GB RAM and Windows 11 (26100.6584).

Before	After

How to reproduce:

These are the simplest steps I could come up with

1. Setup the Example Application https://github.com/zephyrproject-rtos/example-application
2. Change west.yml to point to this PR's source branch and run west update -o=--depth=1 --narrow

3. Run the build with profiling west build --pristine always -b custom_plank app --cmake -- --profiling-format=google-trace --profiling-output=cmake-configure-trace.json
4. Open https://ui.perfetto.dev and open cmake-configure-trace.json in the UI

[sonarqubecloud]

Quality Gate passed

Issues
1 New issue
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[gudnimg]

The ~550ms that are left, half the time seems to go into importing Python modules, and half goes into list_hardware.find_v2_systems(root_args) as all socs are searched with rglob. Perhaps something which can be improved later. If we know the location of board.yml, then we should be able to limit where soc.yml is found by vendor.

Edit: searching SOC vendor by Board vendor won't work. The board may have a custom vendor, while the SOC uses another vendor.