# Revolution Pi Connect SE + Debian Bookworm 64 bit **URL:** \ **Category:** Board Integrations\ **Tags:** mender-convert, raspberry-pi-4\ **Created:** [September 1, 2026, 4:34pm UTC](https://hub.mender.io/t/revolution-pi-connect-se-debian-bookworm-64-bit/8354 "2026-09-01T16:34:16Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![bartvanbos](https://avatars.discourse-cdn.com/v4/letter/b/ac91a4/32.png) [@bartvanbos](https://hub.mender.io/u/bartvanbos)\ **Post date:** [September 1, 2026, 4:34pm UTC](https://hub.mender.io/t/revolution-pi-connect-se-debian-bookworm-64-bit/8354/1 "2026-09-01T16:34:16Z")
The official [Mender documentation](https://docs.mender.io/) explains how Mender works. This is a board-specific complement to the official documentation. _Topic title should be in the format: `` + ``_ **Suggested title:** `Revolution Pi Connect SE + Debian Bookworm 64 bit` # Device description Revolution Pi (Kunbus) is an industrial DIN-rail platform based on the Raspberry Pi Compute Module. The **RevPi Connect SE** uses a **Raspberry Pi Compute Module 4S** (`brcm,bcm2711`, revision type `0x15`). Verified on a working Bullseye Mender image on the same hardware: | Property | Value | | --- | --- | | `/proc/device-tree/model` | `Raspberry Pi Compute Module 4S Rev 1.0` | | `/proc/device-tree/compatible` | `kunbus,revpi-connect-se`, `brcm,bcm2711` | | OS (working control) | Debian 11 (bullseye), kernel `6.1.174-rt51-v8` | There is no dedicated CM4S / Connect SE config in mender-convert. Closest advertised path is the Raspberry Pi 4 Bookworm 64-bit U-Boot config (same SoC family). # Support level | Board / OS | Status | | --- | --- | | RevPi Connect SE + **Debian Bullseye 64-bit** + Mender U-Boot | Works (same U-Boot generation as below) | | RevPi Connect SE + **Debian Bookworm 64-bit** + stock mender-convert | **Does not boot** — early hang after color splash (confirmed) | | Other RevPi variants (Core, Compact, Connect 4/5, …) | Not tested here | **Tested mender-convert versions (Bookworm hang):** - `5.2.1` — hang confirmed on hardware - `master` @ `e7bff87` (`5.2.1-40-ge7bff87`) — **same hang** confirmed on hardware Both pin the same U-Boot asset: `raspberrypi_arm64-2024.04.tar.gz` (Mender branch `mender-rpi-2024.04``Preformatted text`). # Getting started Follow the official guide: [Convert a Mender Debian image](https://docs.mender.io/operating-system-updates-debian-family/convert-a-mender-debian-image). **Input image:** official KUNBUS RevPi Bookworm 64-bit lite, e.g. `2026-03-17-revpi-bookworm-arm64-lite.img`. **Important before convert:** 1. Boot the vendor image once and complete Kunbus first-boot setup (serial / MAC / model) **before** converting, same as for Bullseye integrations. 2. Grow the root partition if needed — the stock lite rootfs is often **100% full** , so `apt` fails while installing Mender packages. Growing root by ~1 GiB is a convert-time prerequisite, not the boot bug below. **Config used for the Bookworm attempt:** ```bash ./docker-build MENDER_ARTIFACT_NAME=revpi-bookworm-1 \ ./docker-mender-convert \ --disk-image input/2026-03-17-revpi-bookworm-arm64-lite-grown.img \ --config configs/raspberrypi/uboot/debian/raspberrypi4_bookworm_64bit_config \ --overlay input/rootfs_overlay_demo ``` That config installs Mender RPi U-Boot as `kernel8.img` (`MENDER_DEVICE_TYPE=raspberrypi4_64`, boot mount `/boot/firmware`). Related Bullseye Hub topic (working path on older OS): [Revolution Pi + Debian Bullseye 64 bit](https://hub.mender.io/t/revolution-pi-debian-bullseye-64-bit/7279). # References - Docs: [Convert a Mender Debian image](https://docs.mender.io/operating-system-updates-debian-family/convert-a-mender-debian-image) - Config: `configs/raspberrypi/uboot/debian/raspberrypi4_bookworm_64bit_config` in [mender-convert](https://github.com/mendersoftware/mender-convert) - U-Boot build script / branch: [build-uboot-rpi64.sh](https://github.com/mendersoftware/mender-convert-integration-scripts/blob/master/build-uboot-rpi64.sh) → `mender-rpi-2024.04` - Golden images: Kunbus / Revolution Pi download portal (Bookworm arm64 lite) - Detailed repro notes (local): `BUG.md` in this tree # Known issues ## Bookworm + Mender U-Boot 2024.04 early hang (primary) **Symptom:** after flashing a stock mender-convert Bookworm image, power-cycle shows the Raspberry Pi color splash, then **nothing** (no multi-user / SSH). UART on Connect SE is not usable for forensics (PiBridge). **Reproduced with:** stock Docker mender-convert on both **`5.2.1` and current `master`** — no custom convert hooks, no third-party U-Boot. Convert itself completes successfully; the failure is at early boot. **Strong evidence (controlled bisect on same hardware):** ```plaintext U-Boot 2024.04 + Bullseye CM4S/RevPi FDT → boots U-Boot 2024.04 + Bookworm CM4S/RevPi FDT → early hang Bookworm Linux + Bookworm CM4S FDT → boots (vendor image, no Mender U-Boot) ``` Replacing only Bookworm `bcm2711-*.dtb` on an otherwise working Bullseye boot VFAT is enough to recreate the hang. So the interesting object is the **firmware-provided BCM2711/RevPi FDT** handed into U-Boot, not the rootfs alone. **Not the primary cause:** missing CM4S model type `0x15` in U-Boot’s `rpi_models_new_scheme[]` (falls back to “Unknown model” / `bcm283x-rpi-other.dtb`). On a working Bullseye Mender image, Linux still sees the real RevPi/CM4S tree (`kunbus,revpi-connect-se` / `brcm,bcm2711`). That means the unknown-model `fdtfile` fallback is **not** what Linux boots from on this Mender path — treat `0x15` support as a separate correctness fix. **Ask to maintainers:** 1. Is Connect SE / CM4S + Bookworm considered supported under `raspberrypi4_bookworm_64bit_config`, or is a dedicated config needed? 2. Can Mender RPi U-Boot **2024.04** be fixed (or a newer `raspberrypi_arm64-*.tar.gz` shipped) to tolerate the Bookworm CM4S/RevPi FDT at `fdt_addr`? 3. Separately: add CM4S revision type `0x15` to the RPi model table. ---
**Author:** ![bartvanbos](https://avatars.discourse-cdn.com/v4/letter/b/ac91a4/32.png) [@bartvanbos](https://hub.mender.io/u/bartvanbos)\ **Post date:** [September 3, 2026, 9:16am UTC](https://hub.mender.io/t/revolution-pi-connect-se-debian-bookworm-64-bit/8354/2 "2026-09-03T09:16:44Z")
**Update** Sept 03/2026 ### RevPi Bookworm U-Boot boot issue — current findings We have now isolated the RevPi boot failure to the Raspberry Pi CM4S device tree. #### What we already knew - Bullseye boots correctly through the Mender U-Boot A/B boot flow. - Bookworm fails very early: rainbow screen, then no further boot or serial output. - Vanilla Bookworm without U-Boot boots correctly. - Replacing `bcm2711-rpi-cm4s.dtb` with the Bullseye version makes the newer image boot again. This identified `bcm2711-rpi-cm4s.dtb` as the root cause area. #### Git bisect We matched the exact Bullseye working DTB and Bookworm failing DTB to Raspberry Pi firmware Git history. Between them: - 222 total firmware commits - 23 commits actually changed `bcm2711-rpi-cm4s.dtb` We used `git bisect` and physically boot-tested the intermediate DTBs. Result: - All tested intermediate DTBs booted correctly. - The final DTB-changing commit introduced the failure. First bad Raspberry Pi firmware commit: `70c596a513fb6a37f26405a40e60733a833a1672` #### Root cause That commit includes a Raspberry Pi device-tree change for the PL011 UART. The working DTs use legacy-compatible PL011 identification, while the failing DT contains: `compatible = "arm,pl011-axi";` U-Boot 2024.04 does not contain a driver match for `arm,pl011-axi`. #### Proof We took the exact known-bad Bookworm DTB and modified only UART0: From: `compatible = "arm,pl011-axi";` to: `compatible = "arm,pl011-axi", "arm,pl011", "arm,primecell";` Nothing else was changed. Result: **the RevPi boots successfully again through Mender/U-Boot.** We also confirmed that patching UART0 alone is sufficient; the other disabled PL011 UART nodes do not need to be changed. ### Conclusion The Bookworm failure is caused by a device-tree compatibility change for UART0. The newer Raspberry Pi DT identifies it only as `arm,pl011-axi`, which U-Boot 2024.04 does not recognize. Restoring the legacy PL011 fallback compatible string makes the exact failing DTB boot successfully. ---
**Author:** ![bartvanbos](https://avatars.discourse-cdn.com/v4/letter/b/ac91a4/32.png) [@bartvanbos](https://hub.mender.io/u/bartvanbos)\ **Post date:** [September 3, 2026, 12:07pm UTC](https://hub.mender.io/t/revolution-pi-connect-se-debian-bookworm-64-bit/8354/3 "2026-09-03T12:07:25Z")
We were able to complete the root-cause investigation and confirm that this issue is caused by a temporary Raspberry Pi Device Tree compatibility regression affecting the PL011 UART definition. Our findings: - Bullseye boots correctly through the Mender/U-Boot A/B flow. - Bookworm fails very early on the Revolution Pi Connect SE. - We isolated the failure to `bcm2711-rpi-cm4s.dtb`. - We matched the working Bullseye DTB and failing Bookworm DTB against the Raspberry Pi firmware Git history and bisected the DTB changes. - The first failing Raspberry Pi firmware commit was: `70c596a513fb6a37f26405a40e60733a833a1672` This introduced the PL011 UART Device Tree change where UART0 was represented as: `compatible = "arm,pl011-axi";` The Mender `mender-rpi-2024.04` U-Boot branch does not contain a driver match for `arm,pl011-axi`. We then performed a controlled test using the exact known-bad Bookworm DTB. We modified only UART0 from: `compatible = "arm,pl011-axi";` to: `compatible = "arm,pl011-axi", "arm,pl011", "arm,primecell";` With only that change, the same Bookworm DTB boots successfully through Mender/U-Boot. Raspberry Pi later restored the legacy fallback compatible strings in this patch: > > > Retain the original compatible strings as fallbacks. > > See: https://github.com/ra…spberrypi/linux/pull/7023 > > Signed-off-by: Phil Elwell \ We have now confirmed that KUNBUS included this backport/fix in their Debian Trixie release: > **[Index of /trixie](https://packages.revolutionpi.com/trixie/)** The KUNBUS Trixie `bcm2711-rpi-cm4s.dtb` contains: `arm,pl011-axi arm,pl011 arm,primecell` and the Revolution Pi Connect SE boots correctly with Trixie through our Mender/U-Boot A/B boot flow. Therefore, this issue is no longer a release blocker for us, as we can proceed with Trixie. That said, it may still be worthwhile for Mender to consider making the `mender-rpi-2024.04` U-Boot branch compatible with `arm,pl011-axi` directly. At present, the U-Boot PL011 drivers match the legacy `arm,pl011` compatible string, but not `arm,pl011-axi`. Supporting the newer compatible string would make the Mender Raspberry Pi boot flow more robust against similar Device Tree changes in the future. ---
**Author:** ![bartvanbos](https://avatars.discourse-cdn.com/v4/letter/b/ac91a4/32.png) [@bartvanbos](https://hub.mender.io/u/bartvanbos)\ **Post date:** [September 4, 2026, 3:33pm UTC](https://hub.mender.io/t/revolution-pi-connect-se-debian-bookworm-64-bit/8354/4 "2026-09-04T15:33:29Z")
We have now completed the root-cause investigation and opened a PR against Mender’s `mender-rpi-2024.04` U-Boot branch: > > > This PR adds two Raspberry Pi Compute Module 4S compatibility fixes to the \`mend…er-rpi-2024.04\` branch. > > \### 1. Add Compute Module 4S board detection > > Raspberry Pi revision type \`0x15\` currently falls through to \`Unknown model\` and uses \`bcm283x-rpi-other.dtb\`. > > This patch maps revision type \`0x15\` to: > > \`bcm2711-rpi-cm4s.dtb\` > > and uses the same onboard Ethernet handling as Compute Module 4. > > \### 2. Add \`arm,pl011-axi\` PL011 compatibility > > Newer Raspberry Pi device trees may describe the PL011 UART as: > > \`compatible = "arm,pl011-axi";\` > > U-Boot 2024.04 currently only matches the legacy \`arm,pl011\` compatible string. As a result, the UART does not bind when the device tree does not provide the legacy fallback. > > This behavior has also been observed in another Raspberry Pi 4 / Mender integration case: > > https://hub.mender.io/t/raspberry-pi-4-stuck-on-boot/8175/5 > > We reproduced and investigated the issue in detail on a Revolution Pi Connect SE / Raspberry Pi Compute Module 4S using the Bookworm \`bcm2711-rpi-cm4s.dtb\`: > > https://hub.mender.io/t/revolution-pi-connect-se-debian-bookworm-64-bit/8354 > > The investigation and support discussion are also tracked in Northern.tech support case: > > https://support.northern.tech/hc/en-us/requests/12515 > > The regression was isolated by bisecting Raspberry Pi firmware DTB changes, and confirmed by modifying only UART0 in the failing DTB from: > > \`compatible = "arm,pl011-axi";\` > > to: > > \`compatible = "arm,pl011-axi", "arm,pl011", "arm,primecell";\` > > With that change, the same image boots successfully through the Mender/U-Boot A/B boot flow. > > Adding \`arm,pl011-axi\` to the generic PL011 driver match table allows U-Boot to work directly with these device trees without depending on the legacy fallback string. > > Raspberry Pi later restored the legacy PL011 fallback compatibles in newer device trees, so current Trixie-based Revolution Pi images are no longer affected. This U-Boot change nevertheless makes the Mender Raspberry Pi bootloader more robust against device trees using \`arm,pl011-axi\` directly. > > These changes are submitted here specifically for the Mender-maintained \`mender-rpi-2024.04\` integration branch. Any corresponding upstream U-Boot changes can be submitted separately through the U-Boot mailing-list process. The issue was narrowed down to the PL011 UART compatibility string in the affected Bookworm `bcm2711-rpi-cm4s.dtb`. The failing DTB exposes UART0 only as: `compatible = "arm,pl011-axi";` while the current Mender U-Boot 2024.04 branch does not match `arm,pl011-axi`. We confirmed the root cause experimentally by taking the exact known-bad DTB and changing only UART0 to: `compatible = "arm,pl011-axi", "arm,pl011", "arm,primecell";` With that single change, the same image boots correctly through the Mender/U-Boot A/B flow. KUNBUS Trixie already contains the later Raspberry Pi backward-compatibility fix, so Trixie is no longer blocked. However, I still think it would be valuable for Mender to merge the U-Boot-side compatibility fix. There are two possible long-term directions: 1. Submit the `arm,pl011-axi` support upstream to U-Boot and wait for it to be accepted and released. 2. Harden the existing Mender `mender-rpi-2024.04` branch now by adding the compatible string to the PL011 driver match table. Upstreaming is absolutely worth considering, and I am happy to look at that as a separate follow-up. But Mender currently maintains a U-Boot branch based around 2024.04, so even if upstream U-Boot accepts the fix, Mender customers would not benefit automatically without either backporting it or moving the Mender integration to a newer U-Boot release. For that reason, I think merging the small compatibility fix into the existing Mender branch is the pragmatic short-term solution. It makes the Mender Raspberry Pi boot flow more resilient to valid Raspberry Pi Device Tree changes and directly benefits users of the current Mender integration, while upstream U-Boot work can continue independently. The same PR also adds explicit Raspberry Pi Compute Module 4S detection, which avoids revision type `0x15` falling through to `Unknown model`. PR: > > > This PR adds two Raspberry Pi Compute Module 4S compatibility fixes to the \`mend…er-rpi-2024.04\` branch. > > \### 1. Add Compute Module 4S board detection > > Raspberry Pi revision type \`0x15\` currently falls through to \`Unknown model\` and uses \`bcm283x-rpi-other.dtb\`. > > This patch maps revision type \`0x15\` to: > > \`bcm2711-rpi-cm4s.dtb\` > > and uses the same onboard Ethernet handling as Compute Module 4. > > \### 2. Add \`arm,pl011-axi\` PL011 compatibility > > Newer Raspberry Pi device trees may describe the PL011 UART as: > > \`compatible = "arm,pl011-axi";\` > > U-Boot 2024.04 currently only matches the legacy \`arm,pl011\` compatible string. As a result, the UART does not bind when the device tree does not provide the legacy fallback. > > This behavior has also been observed in another Raspberry Pi 4 / Mender integration case: > > https://hub.mender.io/t/raspberry-pi-4-stuck-on-boot/8175/5 > > We reproduced and investigated the issue in detail on a Revolution Pi Connect SE / Raspberry Pi Compute Module 4S using the Bookworm \`bcm2711-rpi-cm4s.dtb\`: > > https://hub.mender.io/t/revolution-pi-connect-se-debian-bookworm-64-bit/8354 > > The investigation and support discussion are also tracked in Northern.tech support case: > > https://support.northern.tech/hc/en-us/requests/12515 > > The regression was isolated by bisecting Raspberry Pi firmware DTB changes, and confirmed by modifying only UART0 in the failing DTB from: > > \`compatible = "arm,pl011-axi";\` > > to: > > \`compatible = "arm,pl011-axi", "arm,pl011", "arm,primecell";\` > > With that change, the same image boots successfully through the Mender/U-Boot A/B boot flow. > > Adding \`arm,pl011-axi\` to the generic PL011 driver match table allows U-Boot to work directly with these device trees without depending on the legacy fallback string. > > Raspberry Pi later restored the legacy PL011 fallback compatibles in newer device trees, so current Trixie-based Revolution Pi images are no longer affected. This U-Boot change nevertheless makes the Mender Raspberry Pi bootloader more robust against device trees using \`arm,pl011-axi\` directly. > > These changes are submitted here specifically for the Mender-maintained \`mender-rpi-2024.04\` integration branch. Any corresponding upstream U-Boot changes can be submitted separately through the U-Boot mailing-list process. Hopefully the Mender team can review and consider merging this into `mender-rpi-2024.04`.