Add NXP i.MX 8M Mini (imx8mm) target by miyazakh · Pull Request #931 · wolfSSL/wolfBoot

miyazakh · 2026-10-08T01:35:47Z

Adds wolfBoot support for the NXP i.MX 8M Mini, tested on the TechNexion PICO-IMX8MM (PICO-PI baseboard).

Boot modes

BL33 (default, IMX8MM_BL33=1): wolfBoot replaces U-Boot proper.
BootROM -> U-Boot SPL -> ATF (BL31) -> wolfBoot -> Linux.
wolfBoot reads a signed FIT (kernel + DTB) from eMMC p1 (FAT32, /fitImage_A.itb / /fitImage_B.itb), verifies it and boots Linux at EL2.
RAM-boot (IMX8MM_BL33=0): started from U-Boot proper with go 0x40480000; the signed kernel is bundled after wolfBoot.

Changes

src/sdhci.c: optional eMMC bus width and High Speed timing (SDHCI_EMMC_BUS_WIDTH, SDHCI_EMMC_HS). Defaults unchanged for other targets.
hal/imx8mm.*: UART2 console, uSDHC3 eMMC through the SDHCI layer (register shim from hal/imx8qm.c), identity MMU + D-cache with SDMA cache maintenance in BL33 mode.
config/examples/imx8mm-pico.config, test-app/app_imx8mm.c, Makefile (MAIN_TARGET), 3 CI build jobs.
tools/scripts/imx8mm/: build flash.bin (BL33), the signed FIT, and the go image.
docs/Targets.md: "NXP i.MX 8M Mini" section.

Testing

Built with Ubuntu GCC 13.3 and Linaro GCC 6.4.1 (all CI variants).
On hardware: eMMC standalone boot, A/B slot selection, signature verification and Linux boot (6.1.55 and 6.12.49 with the TechNexion Yocto rootfs). Load + verify of a 27 MB FIT takes about 1.7 s.
Boot chain set up from a fresh clone with u-boot-tn-imx tn-imx_v2023.04_6.1.55_2.2.0-stable and its install_uboot_imx8.sh.

Notes

HABv4 (authentication of wolfBoot itself) is not set up yet.
DTBs from the Linux tree lack /memory and bootargs (U-Boot normally adds them); imx8mm-mkfit.sh adds them before signing.

Copilot

🟡 Changes recommended

The image-generation scripts can reject valid bootargs or produce images that overlap memory or exceed runtime limits.

3 open findings

Validate ELF _end to prevent signed kernel overwrite · New
Append root argument when DTB bootargs lacks root · New
Enforce 42 MiB kernel size limit · New

What changed in this PR

Adds NXP i.MX 8M Mini support for BL33 and U-Boot go boot flows.

Changes:

Adds i.MX8MM HAL, linker layout, configuration, test payload, and CI builds.
Extends SDHCI with configurable eMMC width and High Speed timing.
Adds scripts and documentation for producing signed FIT, go, and flash images.

File	Description
`.github/workflows/test-configs.yml`	Adds three i.MX8MM build variants.
`.gitignore`	Ignores generated i.MX8MM artifacts.
`Makefile`	Defines i.MX8MM build outputs.
`config/examples/imx8mm-pico.config`	Configures PICO-IMX8MM boot modes.
`docs/Targets.md`	Documents setup, booting, and limitations.
`hal/imx8mm.c`	Implements UART, MMU/cache, and uSDHC HAL support.
`hal/imx8mm.h`	Defines i.MX8MM hardware constants.
`hal/imx8mm.ld`	Defines the DRAM memory layout.
`include/sdhci.h`	Adds eMMC High Speed constants.
`src/boot_aarch64.c`	Includes the i.MX8MM platform header.
`src/boot_aarch64_start.S`	Adds i.MX8MM EL2 startup handling.
`src/sdhci.c`	Adds configurable eMMC width and timing.
`test-app/app_imx8mm.c`	Adds a bare-metal boot payload.
`tools/scripts/imx8mm/imx8mm-mkfit.sh`	Builds signed kernel/DTB FIT images.
`tools/scripts/imx8mm/imx8mm-mkflashbin.sh`	Builds BL33 flash images.
`tools/scripts/imx8mm/imx8mm-mkgoimage.sh`	Builds U-Boot `go` images.

🧠 Review effort: Balanced

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wolfSSL-Fenrir-bot

Fenrir Automated Review — PR #931

Scan targets checked: wolfboot-src, wolfboot-bugs
Coverage: 2 of 5 in-scope changed file(s) opened by the reviewer; not opened: include/sdhci.h, src/boot_aarch64.c, test-app/app_imx8mm.c

Fenrir result: Approved ✅

No new issues found in the changed files.

Advisory only — this automated result does not count as a GitHub approval.

Review tier: Lite

dgarske

@miyazakh please resolve merge conflicts

SDHCI_EMMC_BUS_WIDTH (1/4/8, default 4) and SDHCI_EMMC_HS (CMD6 HS_TIMING, 50 MHz). Defaults are unchanged.

Boots a signed Linux kernel, either loaded into DRAM and started from U-Boot proper (RAM-boot, go) or started by ATF as BL33 reading a signed FIT from eMMC (uSDHC3, FAT32). Includes a test app and CI builds.

Scripts for flash.bin (BL33), the signed FIT and the RAM-boot image.

wolfboot.bin omits the BSS that startup clears.

…_SIZE The limit is read from the build configuration.

dgarske · 2026-11-04T17:47:09Z

+
+static volatile uint64_t imx8mm_l1_table[512] __attribute__((aligned(4096)));
+
+static void imx8mm_mmu_enable(void)


Some of this might be better as a pure assembly implementation.

MMU enable and cache range ops implemented in assembly.

dgarske · 2026-11-04T17:47:28Z

+
+#if defined(DISK_EMMC) && !defined(SDHCI_SDMA_DISABLED)
+/* Cache maintenance by address range for SDMA */
+static void imx8mm_dcache_range(uintptr_t start, uint32_t sz, int invalidate)


Same here. Pure assembly.

MMU enable and cache range ops implemented in assembly

dgarske · 2026-11-04T17:48:23Z

@@ -0,0 +1,790 @@
+/* imx8mm.c


If any code in this file also exists in hal/imx8qm.c consider some consolidation and I can regress on the QuadMax.

uSDHC shim shared as hal/imx_usdhc_sdhci.c/.h

dgarske · 2026-11-04T17:48:51Z

+
+/* uSDHC -> SDHCI register shim, taken from hal/imx8qm.c */
+
+#ifndef CADENCE_SRS_OFFSET


Prefer more of the macros like these in the .h

Macros in headers

dgarske · 2026-11-04T17:49:38Z

+#include "hal/imx8mm.h"
+
+/* UART2 console, already set up by the earlier boot stages */
+#define UART_REG(off) \


If the imx8mm.c macros are moved to the .h then you won't need this...

Same above.

dgarske · 2026-11-04T17:50:04Z

+/* Bounded wait for TX FIFO space */
+#define UART_TX_SPIN_MAX  1000000
+
+static void uart_putc(char c)


Should leverage implementation from hal/imx8mm.c

Same above.

dgarske · 2026-11-04T17:50:57Z

+            (dtb & 0x3) != 0) {
+        uart_puts("(pointer not in DRAM or misaligned)\n");
+    }
+    else if (*((volatile uint32_t*)(uintptr_t)dtb) == FDT_MAGIC_LE) {


Perhaps if you are wanting to prove the FDT pointer the test-app should link the fdt.c code too and parse it? No really required tho.

test-app parses the DTB with fdt.c

dgarske · 2026-11-04T17:51:29Z

@@ -0,0 +1,123 @@
+#!/usr/bin/env bash


Duplicating work in tools/scripts/imx8qm/imx8qm-flash.sh. Let's considolidate.

I didn't find much overlap with imx8qm-flash.sh itself. Similar parts are
(1) the bootargs and /memory DTB edits in mkfit, vs hal_dts_fixup() on imx8qm,
(2) flashing over uuu/SD, which imx8mm only prints instructions for, and
(3) the zero-padding when bundling images (mkramimage vs imx8qm-mkflashbin).
Which did you mean, or is it fine as is?

…ssembly

miyazakh · 2026-11-05T08:42:50Z

@dgarske
Tested on PICO-IMX8MM (BL33 and RAM-boot). I have no QuadMax, so could you
regression-test b1c7e4f6 and 176f6c9c there?

miyazakh self-assigned this Oct 8, 2026

Copilot AI balanced review requested due to automatic review settings October 8, 2026 01:35

Copilot started reviewing on behalf of miyazakh October 8, 2026 01:36

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Copilot AI reviewed Oct 8, 2026

View reviewed changes

Comment thread tools/scripts/imx8mm/imx8mm-mkgoimage.sh Resolved

Comment thread tools/scripts/imx8mm/imx8mm-mkfit.sh Resolved

Comment thread tools/scripts/imx8mm/imx8mm-mkgoimage.sh Resolved

miyazakh requested a review from wolfSSL-Fenrir-bot October 8, 2026 02:48

wolfSSL-Fenrir-bot reviewed Oct 8, 2026

View reviewed changes

miyazakh assigned wolfSSL-Bot and unassigned miyazakh Oct 8, 2026

miyazakh force-pushed the imx8mm branch 2 times, most recently from 9454a4f to 42ebd47 Compare October 14, 2026 08:59

danielinux requested a review from dgarske October 30, 2026 08:55

danielinux assigned dgarske Oct 30, 2026

dgarske requested changes Oct 30, 2026

View reviewed changes

dgarske assigned miyazakh Oct 30, 2026

miyazakh added 6 commits October 31, 2026 12:12

sdhci: optional 8-bit bus and High Speed timing for eMMC

d35d926

SDHCI_EMMC_BUS_WIDTH (1/4/8, default 4) and SDHCI_EMMC_HS (CMD6 HS_TIMING, 50 MHz). Defaults are unchanged.

Add NXP i.MX 8M Mini (imx8mm) target

9544ef3

Boots a signed Linux kernel, either loaded into DRAM and started from U-Boot proper (RAM-boot, go) or started by ATF as BL33 reading a signed FIT from eMMC (uSDHC3, FAT32). Includes a test app and CI builds.

imx8mm: add docs and image build scripts

7907434

Scripts for flash.bin (BL33), the signed FIT and the RAM-boot image.

imx8mm: RAM-boot image: check wolfBoot's _end against the kernel offset

114b0ee

wolfboot.bin omits the BSS that startup clears.

imx8mm: mkfit: append root= when bootargs has none

b57e985

imx8mm: RAM-boot image: check the kernel against WOLFBOOT_RAMBOOT_MAX…

9915825

…_SIZE The limit is read from the build configuration.

miyazakh force-pushed the imx8mm branch from 42ebd47 to 9915825 Compare October 31, 2026 04:36

miyazakh removed their assignment Oct 31, 2026

dgarske requested changes Nov 4, 2026

View reviewed changes

dgarske assigned miyazakh Nov 4, 2026

miyazakh added 4 commits November 5, 2026 13:35

imx8mm, imx8qm: share the uSDHC -> SDHCI shim

b1c7e4f

imx8mm, imx8qm: move the identity MMU and SDMA cache maintenance to a…

176f6c9

…ssembly

imx8mm: move macros to headers, use the HAL UART in the test-app

586e553

imx8mm: test-app: parse the DTB with fdt.c

bfaff43


		static volatile uint64_t imx8mm_l1_table[512] __attribute__((aligned(4096)));

		static void imx8mm_mmu_enable(void)


		/* uSDHC -> SDHCI register shim, taken from hal/imx8qm.c */

		#ifndef CADENCE_SRS_OFFSET

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miyazakh commented Oct 8, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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Adds wolfBoot support for the NXP i.MX 8M Mini, tested on the TechNexion PICO-IMX8MM (PICO-PI baseboard).

Boot modes

Changes

Testing

Notes

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🟡 Changes recommended

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Fenrir Automated Review — PR #931

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miyazakh commented Nov 5, 2026

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miyazakh commented Oct 8, 2026 •

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