From a50511de74db08a0b4426be88bb52ce860a008a4 Mon Sep 17 00:00:00 2001
From: builder <build@svrnty.io>
Date: Fri, 22 May 2026 16:10:42 -0400
Subject: [PATCH] grub: EFI-at-/boot fallback for BOOT-less SBC layout in
 Upgrade path

---
 .../v1alpha1/bootloader/grub/upgrade.go       | 43 +++++++++++++++----
 1 file changed, 35 insertions(+), 8 deletions(-)

diff --git a/internal/app/machined/pkg/runtime/v1alpha1/bootloader/grub/upgrade.go b/internal/app/machined/pkg/runtime/v1alpha1/bootloader/grub/upgrade.go
index 9e3f86b84..e99bf2939 100644
--- a/internal/app/machined/pkg/runtime/v1alpha1/bootloader/grub/upgrade.go
+++ b/internal/app/machined/pkg/runtime/v1alpha1/bootloader/grub/upgrade.go
@@ -6,6 +6,7 @@ package grub
 
 import (
 	"context"
+	"fmt"
 	"path/filepath"
 
 	"github.com/siderolabs/go-blockdevice/v2/blkid"
@@ -18,12 +19,12 @@ import (
 
 // Upgrade copies new boot assets and updates grub configuration on an existing installation.
 func (c *Config) Upgrade(opts options.InstallOptions) (*options.InstallResult, error) {
-	mountSpecs := []mount.Spec{
-		{
-			PartitionLabel: constants.BootPartitionLabel,
-			FilesystemType: partition.FilesystemTypeXFS,
-			MountTarget:    filepath.Join(opts.MountPrefix, constants.BootMountPoint),
-		},
+	var mountSpecs []mount.Spec
+
+	bootMountSpec := mount.Spec{
+		PartitionLabel: constants.BootPartitionLabel,
+		FilesystemType: partition.FilesystemTypeXFS,
+		MountTarget:    filepath.Join(opts.MountPrefix, constants.BootMountPoint),
 	}
 
 	efiMountSpec := mount.Spec{
@@ -32,6 +33,23 @@ func (c *Config) Upgrade(opts options.InstallOptions) (*options.InstallResult, e
 		MountTarget:    filepath.Join(opts.MountPrefix, constants.EFIMountPoint),
 	}
 
+	// check if the BOOT partition is present (absent on SBC layouts like RPi5/CM5)
+	if err := mount.PartitionOp(
+		opts.BootDisk,
+		[]mount.Spec{bootMountSpec},
+		func() error {
+			return nil
+		},
+		[]blkid.ProbeOption{
+			blkid.WithSkipLocking(true),
+		},
+		nil,
+		nil,
+		opts.BlkidInfo,
+	); err == nil {
+		mountSpecs = append(mountSpecs, bootMountSpec)
+	}
+
 	var efiFound bool
 
 	// check if the EFI partition is present
@@ -49,12 +67,21 @@ func (c *Config) Upgrade(opts options.InstallOptions) (*options.InstallResult, e
 		opts.BlkidInfo,
 	); err == nil {
 		efiFound = true
-	}
 
-	if efiFound {
+		if len(mountSpecs) == 0 {
+			// No BOOT partition (SBC layout): mount EFI at /boot so GRUB
+			// can find kernel/initramfs/grub.cfg in the expected place.
+			efiMountSpec.MountTarget = filepath.Join(opts.MountPrefix, constants.BootMountPoint)
+			c.bootFromEFI = true
+		}
+
 		mountSpecs = append(mountSpecs, efiMountSpec)
 	}
 
+	if len(mountSpecs) == 0 {
+		return nil, fmt.Errorf("neither BOOT nor EFI partition found on disk %s", opts.BootDisk)
+	}
+
 	err := mount.PartitionOp(
 		opts.BootDisk,
 		mountSpecs,
-- 
2.50.1 (Apple Git-155)