github: workflows: extract zmain build into separate scheduled workflow

Removes the zmain build from the PR/push matrix to reduce noise. Instead, adds a separate `zephyr-main.yml` workflow running on a schedule to maintain early-warning capability. Updates the README with the new status badge.

Author: lrgirdwo

.github/workflows/zephyr-main.yml

@@ -0,0 +1,17 @@
+---
+name: Zephyr Main Branch
+
+# yamllint disable-line rule:truthy
+on:
+  schedule:
+    - cron: '0 4,16 * * *'
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+jobs:
+  zephyr-main-builds:
+    uses: ./.github/workflows/zephyr.yml
+    with:
+      zephyr_revision: 'zmain'

.github/workflows/zephyr.yml

@@ -5,7 +5,17 @@ name: Zephyr
 # 'workflow_dispatch' allows running this workflow manually from the
 # 'Actions' tab
 # yamllint disable-line rule:truthy
-on: [push, pull_request, workflow_dispatch, workflow_call]
+on:
+  push:
+  pull_request:
+  workflow_dispatch:
+  workflow_call:
+    inputs:
+      zephyr_revision:
+        description: 'Zephyr revision to build against'
+        type: string
+        required: false
+        default: 'mnfst'
 
 # Specifies group name that stops previous wokrflows if the name matches
 concurrency:
@@ -112,8 +122,7 @@ jobs:
         # These keys are kept short because Github's left column is not resizable.
         # Search "zephyr_revision" and see below what they expand to.
         zephyr_revision: [
-          mnfst,  # special value: don't override sof/west.yml
-          zmain,  # Zephyr's main branch
+          "${{ inputs.zephyr_revision || 'mnfst' }}"
         ]
         # Using groups to avoid spamming the small results box with too
         # many lines. Pay attention to COMMAS.
@@ -169,7 +178,7 @@ jobs:
           else
              case '${{ matrix.zephyr_revision }}' in
                'zmain') rem_rev='main' ;;
-               *)       echo 'Unknown matrix.zephyr_revision'; exit 1 ;;
+               *)       echo "Unknown matrix.zephyr_revision: ${{ matrix.zephyr_revision }}"; exit 1 ;;
              esac
              ( cd sof/submanifests/
                sed -e "s#=sof_zephyr_revision_override=#${rem_rev}#" \
@@ -192,8 +201,7 @@ jobs:
           # does not use --tags.
           #
           # 2. west fetches using the remote URL, not the remote name. So remote
-          # branches are missing from --decorate below. Cosmetic but annoying;
-          # especially in the "zmain" case.
+          # branches are missing from --decorate below. Cosmetic but annoying.
 
           set -x
           # Fix problem 2. Do NOT assume anything about remote names: nothing is guaranteed.
@@ -227,7 +235,7 @@ jobs:
 
       - name: Upload build artifacts
         uses: actions/upload-artifact@v4
-        if: ${{ matrix.zephyr_revision == 'mnfst' }}
+        if: always()
         with:
           name: linux-build ${{ matrix.build_opts }} ${{ matrix.IPC_platforms }}
           if-no-files-found: error

README.md

@@ -2,6 +2,7 @@
 
 ### Status
 [![Daily Actions](https://github.com/thesofproject/sof/actions/workflows/daily-tests.yml/badge.svg)](https://github.com/thesofproject/sof/actions/workflows/daily-tests.yml)
+[![Zephyr Main Branch](https://github.com/thesofproject/sof/actions/workflows/zephyr-main.yml/badge.svg)](https://github.com/thesofproject/sof/actions/workflows/zephyr-main.yml)
 
 ### Community