[RFC PATCH 16/20] boot: bootdev: add MTD boot device
Daniel Golle
daniel at makrotopia.org
Mon Feb 16 22:23:50 CET 2026
Add a boot device driver for MTD (Memory Technology Devices) that
enables bootstd to scan MTD partitions for FIT images.
Add a mtd_bootdev_hunt() callback that:
- Calls mtd_probe_devices() once to probe all MTD devices (both
UCLASS_MTD and UCLASS_SPI_FLASH) and parse their partitions
- Iterates the MTD subsystem device list and binds an mtd_bootdev for
any top-level MTD device that has partitions but is not in UCLASS_MTD
(those already get their bootdev from mtd_post_bind)
- Uses bootdev_bind() directly since sf_bootdev may already occupy the
standard bootdev child slot
The MTD bootdev calls bootmeth_check() at the start of get_bootflow()
so that only compatible bootmeths (those that accept MTD bootdevs)
produce bootflows. Until bootmeth_openwrt's check() is extended to
accept MTD bootdevs, this driver is inert — each commit compiles and
introduces no regressions independently.
Signed-off-by: Daniel Golle <daniel at makrotopia.org>
---
boot/Kconfig | 9 +++
boot/Makefile | 1 +
boot/mtd_bootdev.c | 150 +++++++++++++++++++++++++++++++++++++++
drivers/mtd/mtd-uclass.c | 15 ++++
4 files changed, 175 insertions(+)
create mode 100644 boot/mtd_bootdev.c
diff --git a/boot/Kconfig b/boot/Kconfig
index d8c7b8360ac..63e373cc62d 100644
--- a/boot/Kconfig
+++ b/boot/Kconfig
@@ -585,6 +585,15 @@ config BOOTMETH_CROS
Note that only x86 devices are supported at present.
+config BOOTDEV_MTD
+ bool "MTD bootdev support"
+ depends on DM_MTD
+ depends on BOOTSTD
+ help
+ Enable a boot device for MTD (Memory Technology Devices).
+ This scans MTD partitions for uImage.FIT firmware images,
+ enabling raw-flash boot via the OpenWrt boot method.
+
config BOOTMETH_OPENWRT
bool "Bootdev support for OpenWrt"
depends on FIT
diff --git a/boot/Makefile b/boot/Makefile
index 7b42358eb0c..feeed4924dd 100644
--- a/boot/Makefile
+++ b/boot/Makefile
@@ -72,6 +72,7 @@ obj-$(CONFIG_$(PHASE_)BOOTMETH_VBE_SIMPLE_FW) += vbe_simple_fw.o
obj-$(CONFIG_$(PHASE_)BOOTMETH_VBE_SIMPLE_OS) += vbe_simple_os.o
obj-$(CONFIG_$(PHASE_)BOOTMETH_ANDROID) += bootmeth_android.o
+obj-$(CONFIG_$(PHASE_)BOOTDEV_MTD) += mtd_bootdev.o
obj-$(CONFIG_$(PHASE_)BOOTMETH_OPENWRT) += bootmeth_openwrt.o
obj-$(CONFIG_IMAGE_LOADER) += image-loader.o
diff --git a/boot/mtd_bootdev.c b/boot/mtd_bootdev.c
new file mode 100644
index 00000000000..8a3304be988
--- /dev/null
+++ b/boot/mtd_bootdev.c
@@ -0,0 +1,150 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * MTD boot device
+ *
+ * Copyright (C) 2026 Daniel Golle <daniel at makrotopia.org>
+ */
+
+#define LOG_CATEGORY UCLASS_BOOTSTD
+
+#include <bootdev.h>
+#include <bootflow.h>
+#include <bootmeth.h>
+#include <dm.h>
+#include <malloc.h>
+#include <mtd.h>
+#include <linux/libfdt.h>
+
+static int mtd_bootdev_get_bootflow(struct udevice *dev,
+ struct bootflow_iter *iter,
+ struct bootflow *bflow)
+{
+ struct udevice *parent = dev_get_parent(dev);
+ struct mtd_info *mtd, *part;
+ u8 buf[40];
+ size_t retlen;
+ char dname[60];
+ int n = 0;
+ int ret;
+
+ ret = bootmeth_check(bflow->method, iter);
+ if (ret)
+ return log_msg_ret("chk", ret);
+
+ /* Find the top-level MTD device matching our parent */
+ mtd_for_each_device(mtd) {
+ if (!mtd_is_partition(mtd) && mtd->dev == parent)
+ break;
+ }
+ if (!mtd || mtd->dev != parent)
+ return log_msg_ret("mtd", -ESHUTDOWN);
+
+ /* Count partitions so the scanning framework knows the bound */
+ list_for_each_entry(part, &mtd->partitions, node)
+ n++;
+ if (n)
+ iter->max_part = n - 1;
+
+ n = 0;
+
+ /* Walk to the iter->part'th sub-partition */
+ list_for_each_entry(part, &mtd->partitions, node) {
+ if (n == iter->part)
+ goto found;
+ n++;
+ }
+ return -ESHUTDOWN;
+
+found:
+ ret = mtd_read(part, 0, sizeof(buf), &retlen, buf);
+ if (ret || retlen < sizeof(buf))
+ return log_msg_ret("rd", -EIO);
+
+ if (fdt_check_header(buf))
+ return log_msg_ret("fdt", -ENOENT);
+
+ /* Device-style name and partition index for bootflow list display */
+ snprintf(dname, sizeof(dname), "%s.part_%x", dev->name, iter->part);
+ bflow->name = strdup(dname);
+ bflow->part = iter->part;
+ bflow->fname = strdup(part->name);
+ bflow->bootmeth_priv = strdup(part->name);
+ bflow->state = BOOTFLOWST_MEDIA;
+
+ return bootmeth_read_bootflow(bflow->method, bflow);
+}
+
+static int mtd_bootdev_bind(struct udevice *dev)
+{
+ struct bootdev_uc_plat *ucp = dev_get_uclass_plat(dev);
+
+ ucp->prio = BOOTDEVP_4_SCAN_FAST;
+
+ return 0;
+}
+
+struct bootdev_ops mtd_bootdev_ops = {
+ .get_bootflow = mtd_bootdev_get_bootflow,
+};
+
+static const struct udevice_id mtd_bootdev_ids[] = {
+ { .compatible = "u-boot,bootdev-mtd" },
+ { }
+};
+
+U_BOOT_DRIVER(mtd_bootdev) = {
+ .name = "mtd_bootdev",
+ .id = UCLASS_BOOTDEV,
+ .ops = &mtd_bootdev_ops,
+ .bind = mtd_bootdev_bind,
+ .of_match = mtd_bootdev_ids,
+};
+
+/**
+ * mtd_bootdev_hunt() - probe MTD devices and bind bootdevs
+ *
+ * Call mtd_probe_devices() to ensure all MTD devices (including SPI NOR
+ * flash via CONFIG_SPI_FLASH_MTD) are probed and their partitions parsed.
+ *
+ * UCLASS_MTD devices already get an mtd_bootdev via mtd_post_bind().
+ * This creates mtd_bootdev instances for other MTD devices (e.g. SPI NOR
+ * in UCLASS_SPI_FLASH) that have partitions but would otherwise lack one.
+ * bootdev_bind() is used directly because sf_bootdev may already occupy
+ * the standard bootdev child slot.
+ */
+static int mtd_bootdev_hunt(struct bootdev_hunter *info, bool show)
+{
+ struct mtd_info *mtd;
+ struct udevice *bdev;
+
+ mtd_probe_devices();
+
+ mtd_for_each_device(mtd) {
+ /* Only top-level MTD devices, not partitions */
+ if (mtd_is_partition(mtd))
+ continue;
+
+ /* Must have a DM device */
+ if (!mtd->dev)
+ continue;
+
+ /* UCLASS_MTD devices already have mtd_bootdev from post_bind */
+ if (device_get_uclass_id(mtd->dev) == UCLASS_MTD)
+ continue;
+
+ /* Only interested in MTD devices that have partitions */
+ if (list_empty(&mtd->partitions))
+ continue;
+
+ bootdev_bind(mtd->dev, "mtd_bootdev", "mtdbootdev", &bdev);
+ }
+
+ return 0;
+}
+
+BOOTDEV_HUNTER(mtd_bootdev_hunter) = {
+ .prio = BOOTDEVP_4_SCAN_FAST,
+ .uclass = UCLASS_MTD,
+ .drv = DM_DRIVER_REF(mtd_bootdev),
+ .hunt = mtd_bootdev_hunt,
+};
diff --git a/drivers/mtd/mtd-uclass.c b/drivers/mtd/mtd-uclass.c
index 720bd824c4d..0c637d3f5ec 100644
--- a/drivers/mtd/mtd-uclass.c
+++ b/drivers/mtd/mtd-uclass.c
@@ -5,11 +5,25 @@
#define LOG_CATEGORY UCLASS_MTD
+#include <bootdev.h>
#include <dm.h>
#include <dm/device-internal.h>
#include <errno.h>
#include <mtd.h>
+static int mtd_post_bind(struct udevice *dev)
+{
+ if (CONFIG_IS_ENABLED(BOOTDEV_MTD)) {
+ int ret;
+
+ ret = bootdev_setup_for_dev(dev, "mtd_bootdev");
+ if (ret)
+ return log_msg_ret("bd", ret);
+ }
+
+ return 0;
+}
+
/*
* Implement a MTD uclass which should include most flash drivers.
* The uclass private is pointed to mtd_info.
@@ -18,5 +32,6 @@
UCLASS_DRIVER(mtd) = {
.id = UCLASS_MTD,
.name = "mtd",
+ .post_bind = mtd_post_bind,
.per_device_auto = sizeof(struct mtd_info),
};
--
2.53.0
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