[PATCH v12 0/2] Support for block device NVMEM providers

[PATCH v12 0/2] Support for block device NVMEM providers

[Loic Poulain]

On embedded devices, it is common for factory provisioning to store
device-specific information, such as Ethernet or WiFi MAC addresses,
in a dedicated area of an eMMC partition. This avoids the need for
and additional EEPROM/OTP and leverages the persistence of eMMC.

One example is the Arduino UNO-Q, where the WiFi MAC address and the
Bluetooth Device address are stored in the eMMC Boot1 partition.

Until now, accessing this information required a custom bootloader
to read the data and inject it into the Device Tree before handing
control over to the kernel. This approach is fragile and leads to
device-specific workarounds.

Rather than adding a new NVMEM provider specifically to the eMMC
subsystem, the new support operates at the block layer, allowing any
block device to behave like other non-volatile memories such as EEPROM
or OTP.

This series builds on earlier work by Daniel Golle that enables block
devices to act as NVMEM providers:
https://lore.kernel.org/all/6061aa4201030b9bb2f8d03ef32a564fdb786ed1.1709667858.git.daniel@makrotopia.org/

Note that this is currently limited to MMC-backed block devices, as
only the MMC core associates a firmware node with the block device
(add_disk_fwnode). This can be easily extended in the future to
support additional block drivers.

Signed-off-by: Loic Poulain <loic.poulain@oss.qualcomm.com>
---
Changes in v12:
- Simplify the series and remove consumer changes (BT/Net) that will be
  submitted separately.
- Link to v11: https://lore.kernel.org/r/20261015-block-as-nvmem-v11-0-f890ac74f87d@oss.qualcomm.com

Changes in v11:
- Rebase on linux-next + resend
- Link to v10: https://lore.kernel.org/r/20260806-block-as-nvmem-v10-0-be598b2a5606@oss.qualcomm.com

Changes in v10:
- block/blk-nvmem: simplify read error handling (Christoph)
- block/blk-nvmem: verify dev_t wasn't reassigned before reading (sashiko)
- block/blk-nvmem: drop __free() cleanup for explicit of_node_put() (Christoph)
- block/blk-nvmem: init static nvmem_config fields at declaration (Christoph)
- block/partitions/of: fix fwnode ref leak on skip/abort/error paths (sashiko)
- Link to v9: https://lore.kernel.org/r/20260730-block-as-nvmem-v9-0-f72935817dbf@oss.qualcomm.com

Changes in v9:
- Add nvmem support for partition blocks, not only disk (Christoph)
- Prevent concurrent exclusive access to the block device on read (Christoph)
- Add comment about nvmem being a side channel for block device access (Christoph)
- Link to v8: https://lore.kernel.org/r/20260703-block-as-nvmem-v8-0-98ae32bfc49a@oss.qualcomm.com

Changes in v8:
- block: Fix bdev->bd_nvmem on registering failure (sashiko)
- net: of_net: of_get_nvmem_eui48() now also rejects all-ones cells (sashiko)
- Bluetooth: mgmt: account for HCI_QUIRK_USE_BDADDR_NVMEM in
  is_configured() and get_missing_options() (sashiko)
- Reword blk-nvmem KCONFIG help text to satisfy checkpatch
- Link to v7: https://lore.kernel.org/r/20260701-block-as-nvmem-v7-0-3fe8205ef0a8@oss.qualcomm.com

Changes in v7:
- Rework bindings/dts so that the eMMC boot partition can be a nvmem fixed-layout
  and not a child of fixed-partition. (Rob)
- Add Support for fixed-layout as the nvmem device node itself
- Remove "block: partitions: of: Skip child nodes without reg property"
  This is no more required in this series and will be submitted separately (Rob)
- Add missing linux/cleanup.h and linux/device.h includes (Bartosz)
- simplify nvmem_register() error path using dev_err_probe() (Bartosz)
- nvmem_device forward declaration to blk_types.h (Bartosz)
- Add hci_dev_get_bd_addr_from_nvmem() kernel-doc for return value (Piotr)
- Link to v6: https://lore.kernel.org/r/20260629-block-as-nvmem-v6-0-f02513dcd46d@oss.qualcomm.com

Changes in v6:
- blk_nvmem_add() returns int, error properly propagated (Bartosz)
- Redundant if (bdev->bd_nvmem) guard removed in blk_nvmem_del() (Bartosz)
- Size guard changed from UINT_MAX → INT_MAX to avoid signed overflow in config.size (sashiko)
- BLK_OPEN_RESTRICT_WRITES removed from blk_nvmem_reg_read() (sashiko)
- Link to v5: https://lore.kernel.org/r/20260612-block-as-nvmem-v5-0-95e0b30fff90@oss.qualcomm.com

Changes in v5:
- Fixed ath10k binding issue + extended commit message (Krzysztof)
- Moved blk-nvmem handling to block core instead of a class_interface
  This allows correct/robust integration with block device life cycle (Bartosz).
- block: partitions: of: Skip child nodes without reg property (sashiko)
- Link to v4: https://lore.kernel.org/r/20260609-block-as-nvmem-v4-0-45712e6b22c6@oss.qualcomm.com

Changes in v4:
- Fix squash issue (dts commit incorrectly squashed) (Konrad)
- Use devres for nvmem resources (Bartosz)
- use __free() destructor helper when possible (Bartosz)
- Fix value return checking for bdev_file_open_by_dev
- Link to v3: https://lore.kernel.org/r/20260608-block-as-nvmem-v3-0-82681f50aa35@oss.qualcomm.com

Changes in v3:
- Fixed missing 'fixed-partitions' compatible in partition (Rob)
- Fixed clashing nvmem cells, document calibration along mac (Sashiko)
- Remove workaround to handle dangling nvmem references after
  unregistering, this is a generic nvmem framework issue handled
  in Bartosz's series:
   https://lore.kernel.org/all/20260429-nvmem-unbind-v3-0-2a694f95395b@oss.qualcomm.com/
- Validate mac (is_valid_ether_addr) before copying to output buffer
- Link to v2: https://lore.kernel.org/r/20260507-block-as-nvmem-v2-0-bf17edd5134e@oss.qualcomm.com

Changes in v2:
- Fix example nvmem-layout cells to use compatible = "mac-base"
- Squash WiFi MAC and Bluetooth BD address consumer patches into the nvmem layout patch
- Fix possible use-after-free in blk-nvmem: bnv (nvmem priv) linked to nvmem lifetime
- Simplify nvmem-cell-names from items: - const: to plain const:
- Factor out common NVMEM EUI-48 retrieval logic
- Reorder changes
- Link to v1: https://lore.kernel.org/r/20260428-block-as-nvmem-v1-0-6ad23e75190a@oss.qualcomm.com

---
Loic Poulain (2):
      block: partitions: of: Attach partition fwnode to the block device
      block: implement NVMEM provider

 block/Kconfig             |  11 +++++
 block/Makefile            |   1 +
 block/blk-nvmem.c         | 112 ++++++++++++++++++++++++++++++++++++++++++++++
 block/blk.h               |   8 ++++
 block/genhd.c             |   4 ++
 block/partitions/check.h  |   1 +
 block/partitions/core.c   |  25 +++++++++--
 block/partitions/of.c     |   3 ++
 include/linux/blk_types.h |   4 ++
 9 files changed, 166 insertions(+), 3 deletions(-)
---
base-commit: 7649ba73f9e7e1e04d0b46213e39c79ae09dd55c
change-id: 20260428-block-as-nvmem-4b308e8bda9a

Best regards,
-- 
Loic Poulain <loic.poulain@oss.qualcomm.com>

[PATCH v12 1/2] block: partitions: of: Attach partition fwnode to the block device

[Loic Poulain]

The OF partition parser reads offset, size and label from each
"fixed-partitions" child node but does not associate that node with the
resulting partition block device. As a result a partition has no
of_node, unlike the whole-disk device which gets its firmware node via
add_disk_fwnode().

Carry the partition's device tree node through the parser and attach it
to the partition's block device with device_set_node(), mirroring the
whole-disk case. This lets consumers describe per-partition properties
in the device tree (for example an NVMEM layout on a partition node) and
look them up through the partition device.

No functional change for existing users, partitions without a matching
device tree node simply get a NULL fwnode.

Reviewed-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Loic Poulain <loic.poulain@oss.qualcomm.com>
---
 block/partitions/check.h |  1 +
 block/partitions/core.c  | 20 +++++++++++++++++---
 block/partitions/of.c    |  3 +++
 3 files changed, 21 insertions(+), 3 deletions(-)

diff --git a/block/partitions/check.h b/block/partitions/check.h
index b0997467b61a54a8a621b9c155c8329289649460..326081499d9a6be730dbd659c110449cfa06921f 100644
--- a/block/partitions/check.h
+++ b/block/partitions/check.h
@@ -17,6 +17,7 @@ struct parsed_partitions {
 		int flags;
 		bool has_info;
 		struct partition_meta_info info;
+		struct fwnode_handle *fwnode;
 	} *parts;
 	int next;
 	int limit;
diff --git a/block/partitions/core.c b/block/partitions/core.c
index b5c59b79ca7cbb28d4d93478ee1c80908f76ee9f..eee954df1ac6ef7dd4f02ad5c9d49aed778bf015 100644
--- a/block/partitions/core.c
+++ b/block/partitions/core.c
@@ -11,6 +11,7 @@
 #include <linux/sysfs.h>
 #include <linux/ctype.h>
 #include <linux/vmalloc.h>
+#include <linux/property.h>
 #include <linux/raid/detect.h>
 #include "check.h"
 
@@ -110,8 +111,17 @@ static struct parsed_partitions *allocate_partitions(struct gendisk *hd)
 	return state;
 }
 
+static void drop_partitions_fwnodes(struct parsed_partitions *state)
+{
+	for (int i = 0; i < state->limit; i++) {
+		fwnode_handle_put(state->parts[i].fwnode);
+		state->parts[i].fwnode = NULL;
+	}
+}
+
 static void free_partitions(struct parsed_partitions *state)
 {
+	drop_partitions_fwnodes(state);
 	vfree(state->parts);
 	kfree(state);
 }
@@ -139,6 +149,7 @@ static struct parsed_partitions *check_partition(struct gendisk *hd)
 
 	i = res = err = 0;
 	while (!res && check_part[i]) {
+		drop_partitions_fwnodes(state);
 		memset(state->parts, 0, state->limit * sizeof(state->parts[0]));
 		res = check_part[i++](state);
 		if (res < 0) {
@@ -247,6 +258,7 @@ static const struct attribute_group *part_attr_groups[] = {
 
 static void part_release(struct device *dev)
 {
+	fwnode_handle_put(dev_fwnode(dev));
 	put_disk(dev_to_bdev(dev)->bd_disk);
 	bdev_drop(dev_to_bdev(dev));
 }
@@ -294,7 +306,8 @@ static const DEVICE_ATTR(whole_disk, 0444, whole_disk_show, NULL);
  */
 static struct block_device *add_partition(struct gendisk *disk, int partno,
 				sector_t start, sector_t len, int flags,
-				struct partition_meta_info *info)
+				struct partition_meta_info *info,
+				struct fwnode_handle *fwnode)
 {
 	dev_t devt = MKDEV(0, 0);
 	struct device *ddev = disk_to_dev(disk);
@@ -343,6 +356,7 @@ static struct block_device *add_partition(struct gendisk *disk, int partno,
 	pdev->class = &block_class;
 	pdev->type = &part_type;
 	pdev->parent = ddev;
+	device_set_node(pdev, fwnode_handle_get(fwnode));
 
 	/* in consecutive minor range? */
 	if (bdev_partno(bdev) < disk->minors) {
@@ -449,7 +463,7 @@ int bdev_add_partition(struct gendisk *disk, int partno, sector_t start,
 	}
 
 	part = add_partition(disk, partno, start, length,
-			ADDPART_FLAG_NONE, NULL);
+			ADDPART_FLAG_NONE, NULL, NULL);
 	ret = PTR_ERR_OR_ZERO(part);
 out:
 	mutex_unlock(&disk->open_mutex);
@@ -564,7 +578,7 @@ static bool blk_add_partition(struct gendisk *disk,
 	}
 
 	part = add_partition(disk, p, from, size, state->parts[p].flags,
-			     &state->parts[p].info);
+			     &state->parts[p].info, state->parts[p].fwnode);
 	if (IS_ERR(part)) {
 		if (PTR_ERR(part) != -ENXIO) {
 			printk(KERN_ERR " %s: p%d could not be added: %pe\n",
diff --git a/block/partitions/of.c b/block/partitions/of.c
index 53664ea06b6540e3d1155141adaafac7286f2d21..4fc7c80c407de42b2b31be2c82e0e6bc2a30c9e3 100644
--- a/block/partitions/of.c
+++ b/block/partitions/of.c
@@ -3,6 +3,7 @@
 #include <linux/blkdev.h>
 #include <linux/major.h>
 #include <linux/of.h>
+#include <linux/property.h>
 #include <linux/string.h>
 #include "check.h"
 
@@ -62,6 +63,8 @@ static void add_of_partition(struct parsed_partitions *state, int slot,
 		partname = of_get_property(np, "name", &len);
 	strscpy(info->volname, partname, sizeof(info->volname));
 
+	state->parts[slot].fwnode = fwnode_handle_get(of_fwnode_handle(np));
+
 	seq_buf_printf(&state->pp_buf, "(%s)", info->volname);
 }
 

-- 
2.34.1

[PATCH v12 2/2] block: implement NVMEM provider

[Loic Poulain]

On embedded devices using an eMMC it is common that one or more partitions
on the eMMC are used to store MAC addresses and Wi-Fi calibration EEPROM
data. Allow referencing the partition in device tree for the kernel and
Wi-Fi drivers accessing it via the NVMEM layer.

NVMEM is registered for a block device whose OF node describes an NVMEM
layout, either via an "nvmem-layout" child or by being a "fixed-layout"
node itself (e.g. an eMMC boot partition associated through its mmc-card
node).

The NVMEM device is a read-only side channel onto a block device.
Each read opens the block device with BLK_OPEN_EXCL to keep other
exclusive openers away for the duration of the access.

Signed-off-by: Loic Poulain <loic.poulain@oss.qualcomm.com>
Reviewed-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>
---
 block/Kconfig             |  11 +++++
 block/Makefile            |   1 +
 block/blk-nvmem.c         | 112 ++++++++++++++++++++++++++++++++++++++++++++++
 block/blk.h               |   8 ++++
 block/genhd.c             |   4 ++
 block/partitions/core.c   |   5 +++
 include/linux/blk_types.h |   4 ++
 7 files changed, 145 insertions(+)

diff --git a/block/Kconfig b/block/Kconfig
index 70e4a66d941ff66ecb0ec34f4f7eff7fd1e4be40..4899ad572c71ffdbb62460d57623216254893ddc 100644
--- a/block/Kconfig
+++ b/block/Kconfig
@@ -209,6 +209,17 @@ config BLK_INLINE_ENCRYPTION_FALLBACK
 	  by falling back to the kernel crypto API when inline
 	  encryption hardware is not present.
 
+config BLK_NVMEM
+	bool "Block device NVMEM provider"
+	depends on OF
+	depends on NVMEM
+	help
+	  Allow block devices (or partitions) to act as NVMEM providers,
+	  exposing factory-provisioned data such as MAC addresses or Wi-Fi
+	  calibration blobs to the drivers that consume them. This is
+	  typically used on embedded devices where such data is stored in a
+	  dedicated area of an eMMC, instead of a separate EEPROM or OTP.
+
 source "block/partitions/Kconfig"
 
 config BLK_PM
diff --git a/block/Makefile b/block/Makefile
index e7bd320e3d6971a8abf584f5de42776bb54e8216..8200297fbcbab304beb4239d0c33da07011c3ed9 100644
--- a/block/Makefile
+++ b/block/Makefile
@@ -39,3 +39,4 @@ obj-$(CONFIG_BLK_INLINE_ENCRYPTION)	+= blk-crypto.o blk-crypto-profile.o \
 					   blk-crypto-sysfs.o
 obj-$(CONFIG_BLK_INLINE_ENCRYPTION_FALLBACK)	+= blk-crypto-fallback.o
 obj-$(CONFIG_BLOCK_HOLDER_DEPRECATED)	+= holder.o
+obj-$(CONFIG_BLK_NVMEM)                += blk-nvmem.o
diff --git a/block/blk-nvmem.c b/block/blk-nvmem.c
new file mode 100644
index 0000000000000000000000000000000000000000..69b69184e16303444c9cb2dc816d5679daeb13c4
--- /dev/null
+++ b/block/blk-nvmem.c
@@ -0,0 +1,112 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * block device NVMEM provider
+ *
+ * Copyright (c) 2024 Daniel Golle <daniel@makrotopia.org>
+ * Copyright (c) Qualcomm Technologies, Inc. and/or its subsidiaries.
+ *
+ * Useful on devices using a whole disk or a partition (e.g. an eMMC boot
+ * partition) to store MAC addresses, Bluetooth addresses or Wi-Fi
+ * calibration EEPROM data.
+ *
+ * The NVMEM device is a side channel onto a block device that stays fully
+ * usable. This is somewhat mitigated by opening the device exclusively.
+ */
+
+#include <linux/device.h>
+#include <linux/file.h>
+#include <linux/fs.h>
+#include <linux/nvmem-provider.h>
+#include <linux/nvmem-consumer.h>
+#include <linux/of.h>
+#include <linux/property.h>
+
+#include "blk.h"
+
+static int blk_nvmem_reg_read(void *priv, unsigned int from,
+			      void *val, size_t bytes)
+{
+	struct block_device *bdev = priv;
+	struct file *bdev_file;
+	loff_t pos = from;
+	ssize_t ret;
+
+	/* open and prevent other exclusive openers */
+	bdev_file = bdev_file_open_by_dev(bdev->bd_dev,
+					  BLK_OPEN_READ | BLK_OPEN_EXCL,
+					  blk_nvmem_reg_read, NULL);
+	if (IS_ERR(bdev_file))
+		return PTR_ERR(bdev_file);
+
+	if (file_bdev(bdev_file) != bdev) {
+		fput(bdev_file);
+		return -ENODEV;
+	}
+
+	ret = kernel_read(bdev_file, val, bytes, &pos);
+	fput(bdev_file);
+
+	if (ret < 0)
+		return ret;
+	if (ret != bytes)
+		return -EIO;
+	return 0;
+}
+
+int blk_nvmem_add(struct block_device *bdev)
+{
+	struct device *dev = &bdev->bd_device;
+	struct device_node *np = dev_of_node(dev);
+	struct nvmem_config config = {
+		.id		= NVMEM_DEVID_NONE,
+		.owner		= THIS_MODULE,
+		.word_size	= 1,
+		.stride		= 1,
+		.read_only	= true,
+		.root_only	= true,
+		.ignore_wp	= true,
+	};
+	struct nvmem_device *nvmem;
+	struct device_node *child;
+
+	/* skip devices which do not have a device tree node */
+	if (!np)
+		return 0;
+
+	/*
+	 * The layout is described either by an "nvmem-layout" child node or
+	 * by the device node itself being a "fixed-layout" container.
+	 */
+	child = of_get_child_by_name(np, "nvmem-layout");
+	if (child)
+		of_node_put(child);
+	else if (!of_device_is_compatible(np, "fixed-layout"))
+		return 0;
+
+	if (bdev_nr_bytes(bdev) > INT_MAX) {
+		dev_warn(dev, "block device too large to be an NVMEM\n");
+		return 0;
+	}
+
+	config.dev = dev;
+	config.name = dev_name(dev);
+	config.priv = bdev;
+	config.reg_read = blk_nvmem_reg_read;
+	config.size = bdev_nr_bytes(bdev);
+	config.of_node = np;
+
+	nvmem = nvmem_register(&config);
+	if (IS_ERR(nvmem))
+		return dev_err_probe(dev, PTR_ERR(nvmem),
+				     "Failed to register NVMEM device\n");
+
+	bdev->bd_nvmem = nvmem;
+
+	return 0;
+}
+
+void blk_nvmem_del(struct block_device *bdev)
+{
+	nvmem_unregister(bdev->bd_nvmem);
+	bdev->bd_nvmem = NULL;
+}
diff --git a/block/blk.h b/block/blk.h
index ed21724726223f777f40be15f82fdeb9da89beb0..4d9e3952b1561a467417482cd516cdc97358d093 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -837,4 +837,12 @@ static inline void blk_debugfs_unlock(struct request_queue *q,
 	memalloc_noio_restore(memflags);
 }
 
+#ifdef CONFIG_BLK_NVMEM
+int blk_nvmem_add(struct block_device *bdev);
+void blk_nvmem_del(struct block_device *bdev);
+#else
+static inline int blk_nvmem_add(struct block_device *bdev) { return 0; }
+static inline void blk_nvmem_del(struct block_device *bdev) {}
+#endif
+
 #endif /* BLK_INTERNAL_H */
diff --git a/block/genhd.c b/block/genhd.c
index 10ca8b4d6eea7ed3910271ca3af74479e2081d6d..6c45b8eb8dfad14fa2fbfa98177154f24af49a07 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -417,6 +417,8 @@ static void add_disk_final(struct gendisk *disk)
 		 */
 		dev_set_uevent_suppress(ddev, 0);
 		disk_uevent(disk, KOBJ_ADD);
+
+		blk_nvmem_add(disk->part0);
 	}
 
 	blk_apply_bdi_limits(disk->bdi, &disk->queue->limits);
@@ -708,6 +710,8 @@ static void __del_gendisk(struct gendisk *disk)
 
 	disk_del_events(disk);
 
+	blk_nvmem_del(disk->part0);
+
 	/*
 	 * Prevent new openers by unlinked the bdev inode.
 	 */
diff --git a/block/partitions/core.c b/block/partitions/core.c
index eee954df1ac6ef7dd4f02ad5c9d49aed778bf015..c83227710584a6feb25c8abae3b319cfae9cce5b 100644
--- a/block/partitions/core.c
+++ b/block/partitions/core.c
@@ -289,6 +289,8 @@ void drop_partition(struct block_device *part)
 	xa_erase(&part->bd_disk->part_tbl, bdev_partno(part));
 	kobject_put(part->bd_holder_dir);
 
+	blk_nvmem_del(part);
+
 	device_del(&part->bd_device);
 	put_device(&part->bd_device);
 }
@@ -406,6 +408,9 @@ static struct block_device *add_partition(struct gendisk *disk, int partno,
 	/* suppress uevent if the disk suppresses it */
 	if (!dev_get_uevent_suppress(ddev))
 		kobject_uevent(&pdev->kobj, KOBJ_ADD);
+
+	blk_nvmem_add(bdev);
+
 	return bdev;
 
 out_del:
diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
index 0cc09b975d8ffbd45ca3dc47533a71f8e8164de6..8026bd763a0710b60b9553a49783efbaf81aeb9f 100644
--- a/include/linux/blk_types.h
+++ b/include/linux/blk_types.h
@@ -15,6 +15,7 @@
 struct bio_set;
 struct bio;
 struct bio_integrity_payload;
+struct nvmem_device;
 struct page;
 struct io_context;
 struct cgroup_subsys_state;
@@ -73,6 +74,9 @@ struct block_device {
 	int			bd_writers;
 #ifdef CONFIG_SECURITY
 	void			*bd_security;
+#endif
+#ifdef CONFIG_BLK_NVMEM
+	struct nvmem_device	*bd_nvmem;
 #endif
 	/*
 	 * keep this out-of-line as it's both big and not needed in the fast

-- 
2.34.1

Re: [PATCH v12 2/2] block: implement NVMEM provider

[Christoph Hellwig]

Looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>