From b7aa10e7fb7b876ffb9a9b2f10018c988a4a803a Mon Sep 17 00:00:00 2001
From: Padreug <padreug@aiolabs.dev>
Date: Wed, 13 May 2026 16:47:07 +0200
Subject: [PATCH] fix(nixos/upboard): force-load eMMC stack in initrd + align
 /boot label
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First Sintra boot from the freshly-flashed eMMC panicked in stage 1:

  An error occurred in stage 1 of the boot process, which must mount
  the root filesystem on '/mnt-root' and then start stage 2.
  mount: can't find /mnt-root/ in /proc/mounts
  stage 2 init script (/mnt-root/nix/store/...nixos-system-bitspire/init) not found
  Kernel panic - not syncing: Attempted to kill init!

Root cause: the UP Board's eMMC controller is enumerated via ACPI
(sdhci-acpi), but the initrd only had sdhci_pci available. /dev/mmcblk*
nodes never materialised in stage 1, so root-by-label resolution
silently failed and switch_root had nothing to chroot into. Tejo (same
hardware module) appears to have been getting lucky with a different
controller binding, or its eMMC firmware exposes PCI-style SDHCI.

  - Add sdhci-acpi + mmc_block to initrd.availableKernelModules so the
    block device infrastructure is present in the early-boot ramdisk.
  - Force-load both via initrd.kernelModules so they're guaranteed to
    fire before stage 1 init runs — leaving them on availableKernel
    Modules alone relies on udev autoload firing in time, which it
    wasn't.

Also a separate-but-adjacent fix in the same module: /boot was
declared as by-label/boot, but make-disk-image.nix with
partitionTableType="efi" labels the FAT partition "ESP". This was
the FIRST boot failure I hit (manually worked around with
`fatlabel /dev/mmcblk0p1 boot` while in the Alpine live image).
Aligning the declared label with what the image build produces means
future flashes don't need that hand-step. douro.nix already used ESP.

Build verified by `nix eval` on the sintra-installed config — initrd
kernelModules now contains [ "sdhci-acpi" "mmc_block" "dm_mod" ].

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
---
 deploy/nixos/hardware/upboard.nix | 20 ++++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

diff --git a/deploy/nixos/hardware/upboard.nix b/deploy/nixos/hardware/upboard.nix
index 163b795..26e2842 100644
--- a/deploy/nixos/hardware/upboard.nix
+++ b/deploy/nixos/hardware/upboard.nix
@@ -24,9 +24,20 @@
       "usb_storage"
       "sd_mod"
       "sdhci_pci"
+      "sdhci-acpi" # UP Board sintra: eMMC controller is ACPI-enumerated, not PCI
+      "mmc_block" # creates /dev/mmcblk* block-device nodes
       "i915"
     ];
 
+    # Force-load the eMMC stack in stage 1 so root-by-label resolves before
+    # the kernel hands off to switch_root. Without this, initramfs panics
+    # with "An error occurred in stage 1 of the boot process" because
+    # /dev/disk/by-label/nixos never materialises in time.
+    initrd.kernelModules = [
+      "sdhci-acpi"
+      "mmc_block"
+    ];
+
     kernelModules = [
       "kvm-intel"
       "i2c-dev"
@@ -45,14 +56,19 @@
     ];
   };
 
-  # Disk layout: GPT with ESP + ext4 root (eMMC on UP Board)
+  # Disk layout: GPT with ESP + ext4 root (eMMC on UP Board).
+  # Labels match what make-disk-image.nix with partitionTableType="efi"
+  # produces — ESP for the FAT partition, nixos for the ext4 root. We
+  # previously expected `by-label/boot` here and had to manually
+  # `fatlabel` the partition post-flash; aligning the label avoids
+  # that hand-step on future re-flashes. (douro.nix already uses ESP.)
   fileSystems."/" = {
     device = "/dev/disk/by-label/nixos";
     fsType = "ext4";
   };
 
   fileSystems."/boot" = {
-    device = "/dev/disk/by-label/boot";
+    device = "/dev/disk/by-label/ESP";
     fsType = "vfat";
   };