[PATCH v5 0/9] Support for block device NVMEM providers

[PATCH v5 0/9] 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/

It also introduces an NVMEM layout description for the Arduino UNO-Q,
allowing device-specific data stored in the eMMC Boot1 partition to
be accessed in a standard way.

WiFi and Ethernet already support retrieving MAC addresses from NVMEM.
Bluetooth requires similar support, which is also addressed.

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 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

---
Daniel Golle (1):
      block: implement NVMEM provider

Loic Poulain (8):
      block: partitions: of: Skip child nodes without reg property
      dt-bindings: mmc: Document support for nvmem-layout
      dt-bindings: net: wireless: qcom,ath10k: Document NVMEM cells
      dt-bindings: bluetooth: qcom: Add NVMEM BD address cell
      net: of_net: Add of_get_nvmem_eui48() helper for EUI-48 lookup
      Bluetooth: hci_sync: Add NVMEM-backed BD address retrieval
      Bluetooth: qca: Set NVMEM BD address quirks when address is invalid
      arm64: dts: qcom: arduino-imola: Describe NVMEM layout for WiFi/BT addresses

 .../devicetree/bindings/mmc/mmc-card.yaml          |  29 ++++++
 .../net/bluetooth/qcom,bluetooth-common.yaml       |   9 ++
 .../bindings/net/wireless/qcom,ath10k.yaml         |  16 +++
 arch/arm64/boot/dts/qcom/qrb2210-arduino-imola.dts |  39 ++++++++
 block/Kconfig                                      |   9 ++
 block/Makefile                                     |   1 +
 block/blk-nvmem.c                                  | 109 +++++++++++++++++++++
 block/blk.h                                        |   8 ++
 block/genhd.c                                      |   4 +
 block/partitions/of.c                              |  20 ++--
 drivers/bluetooth/btqca.c                          |   5 +-
 include/linux/blk_types.h                          |   3 +
 include/linux/blkdev.h                             |   1 +
 include/linux/of_net.h                             |   7 ++
 include/net/bluetooth/hci.h                        |  18 ++++
 net/bluetooth/hci_sync.c                           |  39 +++++++-
 net/core/of_net.c                                  |  49 ++++++---
 17 files changed, 345 insertions(+), 21 deletions(-)
---
base-commit: ccb7390d6cdb23b298a6e2a7028ec134dfc4db10
change-id: 20260428-block-as-nvmem-4b308e8bda9a

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

[PATCH v5 1/9] block: partitions: of: Skip child nodes without reg property

[Loic Poulain]

Child nodes of a fixed-partitions node are not necessarily partition
entries, for example an nvmem-layout node has no reg property. The
current code passes a NULL reg pointer and uninitialized len to the
length check, which can result in a kernel panic or silent failure to
register any partitions.

Fix validate_of_partition() to return a skip indicator when no reg
property is present. Guard add_of_partition() with a reg property
check for the same reason.

Signed-off-by: Loic Poulain <loic.poulain@oss.qualcomm.com>
---
 block/partitions/of.c | 20 +++++++++++++-------
 1 file changed, 13 insertions(+), 7 deletions(-)

diff --git a/block/partitions/of.c b/block/partitions/of.c
index c22b6066109819c71568f73e8db8833d196b1cf6..534e02a9d85f62611d880af9b302d9fd49aa4d46 100644
--- a/block/partitions/of.c
+++ b/block/partitions/of.c
@@ -15,6 +15,10 @@ static int validate_of_partition(struct device_node *np, int slot)
 	int a_cells = of_n_addr_cells(np);
 	int s_cells = of_n_size_cells(np);
 
+	/* Skip nodes without a reg property (e.g. nvmem-layout) */
+	if (!reg)
+		return 1;
+
 	/* Make sure reg len match the expected addr and size cells */
 	if (len / sizeof(*reg) != a_cells + s_cells)
 		return -EINVAL;
@@ -80,14 +84,15 @@ int of_partition(struct parsed_partitions *state)
 	slot = 1;
 	/* Validate parition offset and size */
 	for_each_child_of_node(partitions_np, np) {
-		if (validate_of_partition(np, slot)) {
+		int err = validate_of_partition(np, slot);
+
+		if (err < 0) {
 			of_node_put(np);
 			of_node_put(partitions_np);
-
 			return -1;
 		}
-
-		slot++;
+		if (!err)
+			slot++;
 	}
 
 	slot = 1;
@@ -97,9 +102,10 @@ int of_partition(struct parsed_partitions *state)
 			break;
 		}
 
-		add_of_partition(state, slot, np);
-
-		slot++;
+		if (of_property_present(np, "reg")) {
+			add_of_partition(state, slot, np);
+			slot++;
+		}
 	}
 
 	seq_buf_puts(&state->pp_buf, "\n");

-- 
2.34.1

[PATCH v5 2/9] dt-bindings: mmc: Document support for nvmem-layout

[Loic Poulain]

Add support for an nvmem-layout subnode under an eMMC hardware
partition. This allows the partition to be exposed as an NVMEM
provider and its internal layout to be described. For example,
an eMMC boot partition can be used to store device-specific
information such as a WiFi MAC address.

Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Reviewed-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>
Signed-off-by: Loic Poulain <loic.poulain@oss.qualcomm.com>
---
 .../devicetree/bindings/mmc/mmc-card.yaml          | 29 ++++++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/Documentation/devicetree/bindings/mmc/mmc-card.yaml b/Documentation/devicetree/bindings/mmc/mmc-card.yaml
index a61d6c96df759102f9c1fbfd548b026a77921cae..ca907ad73095925b234b119948f94ae81e698c86 100644
--- a/Documentation/devicetree/bindings/mmc/mmc-card.yaml
+++ b/Documentation/devicetree/bindings/mmc/mmc-card.yaml
@@ -40,6 +40,9 @@ patternProperties:
         contains:
           const: fixed-partitions
 
+      nvmem-layout:
+        $ref: /schemas/nvmem/layouts/nvmem-layout.yaml
+
 required:
   - compatible
   - reg
@@ -86,6 +89,32 @@ examples:
                     read-only;
                 };
             };
+
+            partitions-boot2 {
+                compatible = "fixed-partitions";
+
+                #address-cells = <1>;
+                #size-cells = <1>;
+
+                nvmem-layout {
+                    compatible = "fixed-layout";
+
+                    #address-cells = <1>;
+                    #size-cells = <1>;
+
+                    mac-addr@4400 {
+                        compatible = "mac-base";
+                        reg = <0x4400 0x6>;
+                        #nvmem-cell-cells = <1>;
+                    };
+
+                    bd-addr@5400 {
+                        compatible = "mac-base";
+                        reg = <0x5400 0x6>;
+                        #nvmem-cell-cells = <1>;
+                    };
+                };
+            };
         };
     };
 

-- 
2.34.1

[PATCH v5 3/9] dt-bindings: net: wireless: qcom,ath10k: Document NVMEM cells

[Loic Poulain]

Document the NVMEM cells supported by the ath10k driver, the
mac-address, pre-calibration data, and calibration data.

Since such data may also originate from chipset OTP or be supplied
via other device tree structures. All of these cells are optional
and can be provided independently, in any combination.

Reviewed-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@oss.qualcomm.com>
Signed-off-by: Loic Poulain <loic.poulain@oss.qualcomm.com>
---
 .../devicetree/bindings/net/wireless/qcom,ath10k.yaml    | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/Documentation/devicetree/bindings/net/wireless/qcom,ath10k.yaml b/Documentation/devicetree/bindings/net/wireless/qcom,ath10k.yaml
index c21d66c7cd558ab792524be9afec8b79272d1c87..878c5d833a9cb073520c256c1b72d0f1489e7f4a 100644
--- a/Documentation/devicetree/bindings/net/wireless/qcom,ath10k.yaml
+++ b/Documentation/devicetree/bindings/net/wireless/qcom,ath10k.yaml
@@ -92,6 +92,22 @@ properties:
 
   ieee80211-freq-limit: true
 
+  nvmem-cells:
+    minItems: 1
+    maxItems: 3
+    description:
+      References to nvmem cells for MAC address and/or calibration data.
+      Supported cell names are mac-address, calibration, and pre-calibration.
+
+  nvmem-cell-names:
+    minItems: 1
+    maxItems: 3
+    items:
+      enum:
+        - mac-address
+        - calibration
+        - pre-calibration
+
   qcom,calibration-data:
     $ref: /schemas/types.yaml#/definitions/uint8-array
     description:

-- 
2.34.1

[PATCH v5 4/9] dt-bindings: bluetooth: qcom: Add NVMEM BD address cell

[Loic Poulain]

Add support for an NVMEM cell provider for "local-bd-address",
allowing the Bluetooth stack to retrieve controller's BD address
from non-volatile storage such as an EEPROM or an eMMC partition.

Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Reviewed-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>
Signed-off-by: Loic Poulain <loic.poulain@oss.qualcomm.com>
---
 .../devicetree/bindings/net/bluetooth/qcom,bluetooth-common.yaml | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/Documentation/devicetree/bindings/net/bluetooth/qcom,bluetooth-common.yaml b/Documentation/devicetree/bindings/net/bluetooth/qcom,bluetooth-common.yaml
index c8e9c55c1afb4c8e05ba2dae41ce2db4194b4a0f..7cb28f30c9af032082f23311f2fc89a32f266f17 100644
--- a/Documentation/devicetree/bindings/net/bluetooth/qcom,bluetooth-common.yaml
+++ b/Documentation/devicetree/bindings/net/bluetooth/qcom,bluetooth-common.yaml
@@ -22,4 +22,13 @@ properties:
     description:
       boot firmware is incorrectly passing the address in big-endian order
 
+  nvmem-cells:
+    maxItems: 1
+    description:
+      Nvmem data cell that contains a 6 byte BD address with the most
+      significant byte first (big-endian).
+
+  nvmem-cell-names:
+    const: local-bd-address
+
 additionalProperties: true

-- 
2.34.1

[PATCH v5 5/9] block: implement NVMEM provider

[Loic Poulain]

From: Daniel Golle <daniel@makrotopia.org>

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.

For now, NVMEM is only registered for the whole disk block device, as the
OF node is currently only associated to it.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>
Co-developed-by: Loic Poulain <loic.poulain@oss.qualcomm.com>
Signed-off-by: Loic Poulain <loic.poulain@oss.qualcomm.com>
---
 block/Kconfig             |   9 ++++
 block/Makefile            |   1 +
 block/blk-nvmem.c         | 109 ++++++++++++++++++++++++++++++++++++++++++++++
 block/blk.h               |   8 ++++
 block/genhd.c             |   4 ++
 include/linux/blk_types.h |   3 ++
 include/linux/blkdev.h    |   1 +
 7 files changed, 135 insertions(+)

diff --git a/block/Kconfig b/block/Kconfig
index 15027963472d7b40e27b9097a5993c457b5b3054..0b33747e16dc33473683706f75c92bdf8b648f7c 100644
--- a/block/Kconfig
+++ b/block/Kconfig
@@ -209,6 +209,15 @@ 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,
+	  typically used with eMMC to store MAC addresses or Wi-Fi
+	  calibration data on embedded devices.
+
 source "block/partitions/Kconfig"
 
 config BLK_PM
diff --git a/block/Makefile b/block/Makefile
index 7dce2e44276c4274c11a0a61121c83d9c43d6e0c..d7ac389e71902bc091a8800ea266190a43b3e63d 100644
--- a/block/Makefile
+++ b/block/Makefile
@@ -36,3 +36,4 @@ 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..c005f059d9fe56242ebaef9905673dff902b5686
--- /dev/null
+++ b/block/blk-nvmem.c
@@ -0,0 +1,109 @@
+// 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 partition on an eMMC for MAC addresses or
+ * Wi-Fi calibration EEPROM data.
+ */
+
+#include <linux/file.h>
+#include <linux/nvmem-provider.h>
+#include <linux/nvmem-consumer.h>
+#include <linux/of.h>
+#include <linux/pagemap.h>
+#include <linux/property.h>
+
+#include "blk.h"
+
+static int blk_nvmem_reg_read(void *priv, unsigned int from, void *val, size_t bytes)
+{
+	blk_mode_t mode = BLK_OPEN_READ | BLK_OPEN_RESTRICT_WRITES;
+	dev_t devt = (dev_t)(uintptr_t)priv;
+	size_t bytes_left = bytes;
+	loff_t pos = from;
+	int ret = 0;
+
+	struct file *bdev_file __free(fput) = bdev_file_open_by_dev(devt, mode, priv, NULL);
+	if (IS_ERR(bdev_file))
+		return PTR_ERR(bdev_file);
+
+	while (bytes_left) {
+		pgoff_t f_index = pos >> PAGE_SHIFT;
+		struct folio *folio;
+		size_t folio_off;
+		size_t to_read;
+
+		folio = read_mapping_folio(bdev_file->f_mapping, f_index, NULL);
+		if (IS_ERR(folio)) {
+			ret = PTR_ERR(folio);
+			break;
+		}
+
+		folio_off = offset_in_folio(folio, pos);
+		to_read = min(bytes_left, folio_size(folio) - folio_off);
+		memcpy_from_folio(val, folio, folio_off, to_read);
+		pos += to_read;
+		bytes_left -= to_read;
+		val += to_read;
+		folio_put(folio);
+	}
+
+	return ret;
+}
+
+void blk_nvmem_add(struct block_device *bdev)
+{
+	struct device *dev = &bdev->bd_device;
+	struct nvmem_config config = {};
+
+	/* skip devices which do not have a device tree node */
+	if (!dev_of_node(dev))
+		return;
+
+	/* skip devices without an nvmem layout defined */
+	struct device_node *child __free(device_node) =
+		of_get_child_by_name(dev_of_node(dev), "nvmem-layout");
+	if (!child)
+		return;
+
+	/*
+	 * skip block device too large to be represented as NVMEM devices,
+	 * the NVMEM reg_read callback uses an unsigned int offset
+	 */
+	if (bdev_nr_bytes(bdev) > UINT_MAX) {
+		dev_warn(dev, "block device too large to be an NVMEM provider\n");
+		return;
+	}
+
+	config.id = NVMEM_DEVID_NONE;
+	config.dev = dev;
+	config.name = dev_name(dev);
+	config.owner = THIS_MODULE;
+	config.priv = (void *)(uintptr_t)dev->devt;
+	config.reg_read = blk_nvmem_reg_read;
+	config.size = bdev_nr_bytes(bdev);
+	config.word_size = 1;
+	config.stride = 1;
+	config.read_only = true;
+	config.root_only = true;
+	config.ignore_wp = true;
+	config.of_node = to_of_node(dev->fwnode);
+
+	bdev->bd_nvmem = nvmem_register(&config);
+	if (IS_ERR(bdev->bd_nvmem)) {
+		dev_err_probe(dev, PTR_ERR(bdev->bd_nvmem),
+			      "Failed to register NVMEM device\n");
+		bdev->bd_nvmem = NULL;
+	}
+}
+
+void blk_nvmem_del(struct block_device *bdev)
+{
+	if (bdev->bd_nvmem)
+		nvmem_unregister(bdev->bd_nvmem);
+
+	bdev->bd_nvmem = NULL;
+}
diff --git a/block/blk.h b/block/blk.h
index ec4674cdf2ead4fd259ff5fc42401f591e684ee9..cd3c7ca723391c40be56f1dd4810e641b7c8a2b3 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -757,4 +757,12 @@ static inline void blk_debugfs_unlock(struct request_queue *q,
 	memalloc_noio_restore(memflags);
 }
 
+#ifdef CONFIG_BLK_NVMEM
+void blk_nvmem_add(struct block_device *bdev);
+void blk_nvmem_del(struct block_device *bdev);
+#else
+static inline void blk_nvmem_add(struct block_device *bdev) {}
+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 7d6854fd28e95ae9134309679a7c6a937f5b7db8..1b2382de6fb30c1e5f60f45c04dc03ed3bf5d5f2 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -421,6 +421,8 @@ 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);
@@ -704,6 +706,8 @@ 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/include/linux/blk_types.h b/include/linux/blk_types.h
index 8808ee76e73c09e0ceaac41ba59e86fb0c4efc64..ace6f59b860d0813665b2f62a1c03a1f4be94059 100644
--- a/include/linux/blk_types.h
+++ b/include/linux/blk_types.h
@@ -73,6 +73,9 @@ 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
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 890128cdea1ce66863c5baa36f3b336ec4550807..f15d2b5bf9e4fd2368b8a70416a978e22c0d4333 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -30,6 +30,7 @@
 
 struct module;
 struct request_queue;
+struct nvmem_device;
 struct elevator_queue;
 struct blk_trace;
 struct request;

-- 
2.34.1

[PATCH v5 6/9] net: of_net: Add of_get_nvmem_eui48() helper for EUI-48 lookup

[Loic Poulain]

Factor out the common NVMEM EUI-48 retrieval logic from
of_get_mac_address_nvmem() into a new of_get_nvmem_eui48() helper that
accepts the NVMEM cell name as a parameter. This allows other subsystems
(e.g. Bluetooth) to reuse the same lookup-validate-copy pattern with a
different cell name, without duplicating code.

of_get_mac_address_nvmem() is updated to call of_get_nvmem_eui48() with
"mac-address", preserving its existing behavior.

Reviewed-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>
Signed-off-by: Loic Poulain <loic.poulain@oss.qualcomm.com>
---
 include/linux/of_net.h |  7 +++++++
 net/core/of_net.c      | 49 +++++++++++++++++++++++++++++++++++++------------
 2 files changed, 44 insertions(+), 12 deletions(-)

diff --git a/include/linux/of_net.h b/include/linux/of_net.h
index d88715a0b3a52f87af23d47791bea3baf5be5200..7854ba555d9a55f3d020a37fe00a27ae52e0e5dc 100644
--- a/include/linux/of_net.h
+++ b/include/linux/of_net.h
@@ -15,6 +15,7 @@ struct net_device;
 extern int of_get_phy_mode(struct device_node *np, phy_interface_t *interface);
 extern int of_get_mac_address(struct device_node *np, u8 *mac);
 extern int of_get_mac_address_nvmem(struct device_node *np, u8 *mac);
+int of_get_nvmem_eui48(struct device_node *np, const char *cell_name, u8 *addr);
 int of_get_ethdev_address(struct device_node *np, struct net_device *dev);
 extern struct net_device *of_find_net_device_by_node(struct device_node *np);
 #else
@@ -34,6 +35,12 @@ static inline int of_get_mac_address_nvmem(struct device_node *np, u8 *mac)
 	return -ENODEV;
 }
 
+static inline int of_get_nvmem_eui48(struct device_node *np,
+				      const char *cell_name, u8 *addr)
+{
+	return -ENODEV;
+}
+
 static inline int of_get_ethdev_address(struct device_node *np, struct net_device *dev)
 {
 	return -ENODEV;
diff --git a/net/core/of_net.c b/net/core/of_net.c
index 93ea425b9248a23f4f95a336e9cdbf0053248e32..11c1acca151266ac9287457b4050a54b08e2b5f5 100644
--- a/net/core/of_net.c
+++ b/net/core/of_net.c
@@ -61,9 +61,7 @@ static int of_get_mac_addr(struct device_node *np, const char *name, u8 *addr)
 int of_get_mac_address_nvmem(struct device_node *np, u8 *addr)
 {
 	struct platform_device *pdev = of_find_device_by_node(np);
-	struct nvmem_cell *cell;
-	const void *mac;
-	size_t len;
+	u8 mac[ETH_ALEN] __aligned(sizeof(u16));
 	int ret;
 
 	/* Try lookup by device first, there might be a nvmem_cell_lookup
@@ -75,27 +73,54 @@ int of_get_mac_address_nvmem(struct device_node *np, u8 *addr)
 		return ret;
 	}
 
-	cell = of_nvmem_cell_get(np, "mac-address");
+	ret = of_get_nvmem_eui48(np, "mac-address", mac);
+	if (ret)
+		return ret;
+
+	if (!is_valid_ether_addr(mac))
+		return -EINVAL;
+
+	ether_addr_copy(addr, mac);
+	return 0;
+}
+EXPORT_SYMBOL(of_get_mac_address_nvmem);
+
+/**
+ * of_get_nvmem_eui48 - Read a 6-byte EUI-48 address from a named NVMEM cell.
+ * @np:		Device node to look up the NVMEM cell from.
+ * @cell_name:	Name of the NVMEM cell (e.g. "mac-address", "local-bd-address").
+ * @addr:	Output buffer for the 6-byte address.
+ *
+ * Reads the named NVMEM cell and validates that it contains a non-zero 6-byte
+ * address. Returns 0 on success, negative errno on failure.
+ */
+int of_get_nvmem_eui48(struct device_node *np, const char *cell_name, u8 *addr)
+{
+	struct nvmem_cell *cell;
+	const void *eui48;
+	size_t len;
+
+	cell = of_nvmem_cell_get(np, cell_name);
 	if (IS_ERR(cell))
 		return PTR_ERR(cell);
 
-	mac = nvmem_cell_read(cell, &len);
+	eui48 = nvmem_cell_read(cell, &len);
 	nvmem_cell_put(cell);
 
-	if (IS_ERR(mac))
-		return PTR_ERR(mac);
+	if (IS_ERR(eui48))
+		return PTR_ERR(eui48);
 
-	if (len != ETH_ALEN || !is_valid_ether_addr(mac)) {
-		kfree(mac);
+	if (len != ETH_ALEN || !memchr_inv(eui48, 0, ETH_ALEN)) {
+		kfree(eui48);
 		return -EINVAL;
 	}
 
-	memcpy(addr, mac, ETH_ALEN);
-	kfree(mac);
+	memcpy(addr, eui48, ETH_ALEN);
+	kfree(eui48);
 
 	return 0;
 }
-EXPORT_SYMBOL(of_get_mac_address_nvmem);
+EXPORT_SYMBOL_GPL(of_get_nvmem_eui48);
 
 /**
  * of_get_mac_address()

-- 
2.34.1

[PATCH v5 7/9] Bluetooth: hci_sync: Add NVMEM-backed BD address retrieval

[Loic Poulain]

Some devices store the Bluetooth BD address in non-volatile
memory, which can be accessed through the NVMEM framework.
Similar to Ethernet or WiFi MAC addresses, add support for
reading the BD address from a 'local-bd-address' NVMEM cell.

As with the device-tree provided BD address, add a quirk to
indicate whether a device or platform should attempt to read
the address from NVMEM when no valid in-chip address is present.
Also add a quirk to indicate if the address is stored in
big-endian byte order.

Reviewed-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>
Signed-off-by: Loic Poulain <loic.poulain@oss.qualcomm.com>
---
 include/net/bluetooth/hci.h | 18 ++++++++++++++++++
 net/bluetooth/hci_sync.c    | 39 ++++++++++++++++++++++++++++++++++++++-
 2 files changed, 56 insertions(+), 1 deletion(-)

diff --git a/include/net/bluetooth/hci.h b/include/net/bluetooth/hci.h
index 572b1c620c5d653a1fe10b26c1b0ba33e8f4968f..7686466d1109253b0d75edeb5f6a99fb98ce4cc6 100644
--- a/include/net/bluetooth/hci.h
+++ b/include/net/bluetooth/hci.h
@@ -164,6 +164,24 @@ enum {
 	 */
 	HCI_QUIRK_BDADDR_PROPERTY_BROKEN,
 
+	/* When this quirk is set, the public Bluetooth address
+	 * initially reported by HCI Read BD Address command
+	 * is considered invalid. The public BD Address can be
+	 * retrieved via a 'local-bd-address' NVMEM cell.
+	 *
+	 * This quirk can be set before hci_register_dev is called or
+	 * during the hdev->setup vendor callback.
+	 */
+	HCI_QUIRK_USE_BDADDR_NVMEM,
+
+	/* When this quirk is set, the Bluetooth Device Address provided by
+	 * the 'local-bd-address' NVMEM is stored in big-endian order.
+	 *
+	 * This quirk can be set before hci_register_dev is called or
+	 * during the hdev->setup vendor callback.
+	 */
+	HCI_QUIRK_BDADDR_NVMEM_BE,
+
 	/* When this quirk is set, the duplicate filtering during
 	 * scanning is based on Bluetooth devices addresses. To allow
 	 * RSSI based updates, restart scanning if needed.
diff --git a/net/bluetooth/hci_sync.c b/net/bluetooth/hci_sync.c
index fd3aacdea512a37c22b9a2be90c89ddca4b4d99f..589ccdfa26c1281d6eb979370523fff0d7920302 100644
--- a/net/bluetooth/hci_sync.c
+++ b/net/bluetooth/hci_sync.c
@@ -7,6 +7,7 @@
  */
 
 #include <linux/property.h>
+#include <linux/of_net.h>
 
 #include <net/bluetooth/bluetooth.h>
 #include <net/bluetooth/hci_core.h>
@@ -3588,6 +3589,37 @@ int hci_powered_update_sync(struct hci_dev *hdev)
 	return 0;
 }
 
+/**
+ * hci_dev_get_bd_addr_from_nvmem - Get the Bluetooth Device Address
+ *				    (BD_ADDR) for a HCI device from
+ *				    an NVMEM cell.
+ * @hdev:	The HCI device
+ *
+ * Search for 'local-bd-address' NVMEM cell in the device firmware node.
+ *
+ * All-zero BD addresses are rejected (unprovisioned).
+ */
+static int hci_dev_get_bd_addr_from_nvmem(struct hci_dev *hdev)
+{
+	struct device_node *np = dev_of_node(hdev->dev.parent);
+	u8 ba[sizeof(bdaddr_t)];
+	int err;
+
+	if (!np)
+		return -ENODEV;
+
+	err = of_get_nvmem_eui48(np, "local-bd-address", ba);
+	if (err)
+		return err;
+
+	if (hci_test_quirk(hdev, HCI_QUIRK_BDADDR_NVMEM_BE))
+		baswap(&hdev->public_addr, (bdaddr_t *)ba);
+	else
+		bacpy(&hdev->public_addr, (bdaddr_t *)ba);
+
+	return 0;
+}
+
 /**
  * hci_dev_get_bd_addr_from_property - Get the Bluetooth Device Address
  *				       (BD_ADDR) for a HCI device from
@@ -5042,12 +5074,17 @@ static int hci_dev_setup_sync(struct hci_dev *hdev)
 	 * its setup callback.
 	 */
 	invalid_bdaddr = hci_test_quirk(hdev, HCI_QUIRK_INVALID_BDADDR) ||
-			 hci_test_quirk(hdev, HCI_QUIRK_USE_BDADDR_PROPERTY);
+			 hci_test_quirk(hdev, HCI_QUIRK_USE_BDADDR_PROPERTY) ||
+			 hci_test_quirk(hdev, HCI_QUIRK_USE_BDADDR_NVMEM);
 	if (!ret) {
 		if (hci_test_quirk(hdev, HCI_QUIRK_USE_BDADDR_PROPERTY) &&
 		    !bacmp(&hdev->public_addr, BDADDR_ANY))
 			hci_dev_get_bd_addr_from_property(hdev);
 
+		if (hci_test_quirk(hdev, HCI_QUIRK_USE_BDADDR_NVMEM) &&
+		    !bacmp(&hdev->public_addr, BDADDR_ANY))
+			hci_dev_get_bd_addr_from_nvmem(hdev);
+
 		if (invalid_bdaddr && bacmp(&hdev->public_addr, BDADDR_ANY) &&
 		    hdev->set_bdaddr) {
 			ret = hdev->set_bdaddr(hdev, &hdev->public_addr);

-- 
2.34.1

[PATCH v5 8/9] Bluetooth: qca: Set NVMEM BD address quirks when address is invalid

[Loic Poulain]

When the controller BD address is invalid (zero or default),
set the NVMEM quirks to allow retrieving the address from a
'local-bd-address' NVMEM cell. The BD address is often stored
alongside the WiFi MAC address in big-endian format, so also
set the big-endian quirk.

Reviewed-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>
Signed-off-by: Loic Poulain <loic.poulain@oss.qualcomm.com>
---
 drivers/bluetooth/btqca.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/bluetooth/btqca.c b/drivers/bluetooth/btqca.c
index dda76365726f0bfe0e80e05fe04859fa4f0592e1..df33eacfd29fa680f393f90215150743e6001d5b 100644
--- a/drivers/bluetooth/btqca.c
+++ b/drivers/bluetooth/btqca.c
@@ -721,8 +721,11 @@ static int qca_check_bdaddr(struct hci_dev *hdev, const struct qca_fw_config *co
 	}
 
 	bda = (struct hci_rp_read_bd_addr *)skb->data;
-	if (!bacmp(&bda->bdaddr, &config->bdaddr))
+	if (!bacmp(&bda->bdaddr, &config->bdaddr)) {
 		hci_set_quirk(hdev, HCI_QUIRK_USE_BDADDR_PROPERTY);
+		hci_set_quirk(hdev, HCI_QUIRK_USE_BDADDR_NVMEM);
+		hci_set_quirk(hdev, HCI_QUIRK_BDADDR_NVMEM_BE);
+	}
 
 	kfree_skb(skb);
 

-- 
2.34.1

[PATCH v5 9/9] arm64: dts: qcom: arduino-imola: Describe NVMEM layout for WiFi/BT addresses

[Loic Poulain]

On Arduino Uno-Q, the eMMC boot1 partition is factory provisioned
with device-specific information such as the WiFi MAC address
and the Bluetooth BD address. This partition can serve as an
alternative to additional non-volatile memory, such as a
dedicated EEPROM.

The eMMC boot partitions are typically good candidates, as they
are relatively small, read-only by default (and can be enforced
as hardware read-only), and are not affected by board reflashing
procedures, which generally target the eMMC user or GP partitions.

Describe the corresponding nvmem-layout for the WiFi and Bluetooth
addresses, and point the WiFi and Bluetooth nodes to the appropriate
NVMEM cells to retrieve them.

Reviewed-by: Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>
Reviewed-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>
Signed-off-by: Loic Poulain <loic.poulain@oss.qualcomm.com>
---
 arch/arm64/boot/dts/qcom/qrb2210-arduino-imola.dts | 39 ++++++++++++++++++++++
 1 file changed, 39 insertions(+)

diff --git a/arch/arm64/boot/dts/qcom/qrb2210-arduino-imola.dts b/arch/arm64/boot/dts/qcom/qrb2210-arduino-imola.dts
index bf088fa9807f040f0c8f405f9111b01790b09377..128c7a7e76b5b089044745f5d6407d6391055fc2 100644
--- a/arch/arm64/boot/dts/qcom/qrb2210-arduino-imola.dts
+++ b/arch/arm64/boot/dts/qcom/qrb2210-arduino-imola.dts
@@ -409,7 +409,40 @@ &sdhc_1 {
 	no-sdio;
 	no-sd;
 
+	#address-cells = <1>;
+	#size-cells = <0>;
+
 	status = "okay";
+
+	card@0 {
+		compatible = "mmc-card";
+		reg = <0>;
+
+		partitions-boot1 {
+			compatible = "fixed-partitions";
+
+			#address-cells = <1>;
+			#size-cells = <1>;
+
+			nvmem-layout {
+				compatible = "fixed-layout";
+				#address-cells = <1>;
+				#size-cells = <1>;
+
+				wifi_mac_addr: mac-addr@4400 {
+					compatible = "mac-base";
+					reg = <0x4400 0x6>;
+					#nvmem-cell-cells = <1>;
+				};
+
+				bd_addr: bd-addr@5400 {
+					compatible = "mac-base";
+					reg = <0x5400 0x6>;
+					#nvmem-cell-cells = <1>;
+				};
+			};
+		};
+	};
 };
 
 &spi5 {
@@ -512,6 +545,9 @@ bluetooth {
 		vddch0-supply = <&pm4125_l22>;
 		enable-gpios = <&tlmm 87 GPIO_ACTIVE_HIGH>;
 		max-speed = <3000000>;
+
+		nvmem-cells = <&bd_addr 0>;
+		nvmem-cell-names = "local-bd-address";
 	};
 };
 
@@ -557,6 +593,9 @@ &wifi {
 	qcom,ath10k-calibration-variant = "ArduinoImola";
 	firmware-name = "qcm2290";
 
+	nvmem-cells = <&wifi_mac_addr 0>;
+	nvmem-cell-names = "mac-address";
+
 	status = "okay";
 };
 

-- 
2.34.1

Re: [PATCH v5 5/9] block: implement NVMEM provider

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 5 potential issue(s) to consider:
- [High] NVMEM provider opens the block device with exclusive write restriction, causing conflicts on mounted systems.
- [High] Hardcoded 4GB size limit incorrectly rejects modern eMMC devices.
- [High] Integer overflow in size assignment exposes massive out-of-bounds size.
- [High] Stale `dev_t` reference can cause data leaks across block device hotplugs (ABA problem).
- [High] Using `__free(fput)` defers block device claim release, creating race conditions.
--

commit 459b659c960efdc8a9e2177c5bc4f832e7ee5730
Author: Daniel Golle <daniel@makrotopia.org>

block: implement NVMEM provider

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.

> diff --git a/block/blk-nvmem.c b/block/blk-nvmem.c
> new file mode 100644
> index 0000000000000..c005f059d9fe5
> --- /dev/null
> +++ b/block/blk-nvmem.c
> @@ -0,0 +1,109 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
[ ... ]
> +static int blk_nvmem_reg_read(void *priv, unsigned int from, void *val, size_t bytes)
> +{
> +	blk_mode_t mode = BLK_OPEN_READ | BLK_OPEN_RESTRICT_WRITES;

[Severity: High]
Since the NVMEM provider claims the whole disk (disk->part0), will opening it
with BLK_OPEN_RESTRICT_WRITES and an exclusive holder (priv) return -EBUSY if
any partition on the disk is already mounted or opened for writing?

> +	dev_t devt = (dev_t)(uintptr_t)priv;
> +	size_t bytes_left = bytes;
> +	loff_t pos = from;
> +	int ret = 0;
> +
> +	struct file *bdev_file __free(fput) = bdev_file_open_by_dev(devt, mode, priv, NULL);

[Severity: High]
Does using __free(fput) defer the release of the block device claim? Because
fput() schedules the file release asynchronously, could another subsystem
trying to mount or claim the device immediately after an NVMEM read
sporadically fail with -EBUSY?

Should this use bdev_fput() instead to synchronously yield the claim before
the rest of the file release?

> +	if (IS_ERR(bdev_file))
> +		return PTR_ERR(bdev_file);
[ ... ]
> +void blk_nvmem_add(struct block_device *bdev)
> +{
[ ... ]
> +	/*
> +	 * skip block device too large to be represented as NVMEM devices,
> +	 * the NVMEM reg_read callback uses an unsigned int offset
> +	 */
> +	if (bdev_nr_bytes(bdev) > UINT_MAX) {

[Severity: High]
Since the NVMEM provider is registered against the whole disk rather than the
individual NVMEM partition, does this 4GB limit incorrectly reject most modern
eMMC devices?

> +		dev_warn(dev, "block device too large to be an NVMEM provider\n");
> +		return;
> +	}
> +
> +	config.id = NVMEM_DEVID_NONE;
> +	config.dev = dev;
> +	config.name = dev_name(dev);
> +	config.owner = THIS_MODULE;
> +	config.priv = (void *)(uintptr_t)dev->devt;

[Severity: High]
Can storing the ephemeral dev_t identifier without holding a pinned block
device reference cause an ABA problem?

If the block device is removed, blk_nvmem_del() calls nvmem_unregister()
which drops a reference but does not synchronously wait for consumers to
close. If a new device is plugged in and reuses the same dev_t, could a
consumer reading from the still-alive NVMEM device inadvertently access the
unrelated new block device?

> +	config.reg_read = blk_nvmem_reg_read;
> +	config.size = bdev_nr_bytes(bdev);

[Severity: High]
Can this assignment cause an integer overflow?

The config.size field in struct nvmem_config is a signed 32-bit int, so disk
sizes between 2GB and 4GB will overflow to a negative value. When
nvmem_register() sign-extends this into its 64-bit size_t field, won't it
result in a massive out-of-bounds size being exposed via sysfs?

> +	config.word_size = 1;
> +	config.stride = 1;
> +	config.read_only = true;

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260612-block-as-nvmem-v5-0-95e0b30fff90@oss.qualcomm.com?part=5

Re: [PATCH v5 1/9] block: partitions: of: Skip child nodes without reg property

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 3 potential issue(s) to consider:

Pre-existing issues:
- [High] The device node reference for `partitions_np` is acquired but leaked on both the success and incompatibility early-return paths.
- [High] Potential NULL pointer dereference in `strscpy()` if a partition node lacks both `label` and `name` properties.
- [High] Malicious device tree properties `#address-cells` and `#size-cells` can cause integer underflow, bypassing the length check and leading to massive out-of-bounds reads.
--

commit a6b306502d7065c56b83fd73a46be12067fb56e3
Author: Loic Poulain <loic.poulain@oss.qualcomm.com>

block: partitions: of: Skip child nodes without reg property
    
Child nodes of a fixed-partitions node are not necessarily partition
entries, for example an nvmem-layout node has no reg property. The
current code passes a NULL reg pointer and uninitialized len to the
length check, which can result in a kernel panic or silent failure to
register any partitions.

> diff --git a/block/partitions/of.c b/block/partitions/of.c
> index c22b606610981..534e02a9d85f6 100644
> --- a/block/partitions/of.c
> +++ b/block/partitions/of.c
> @@ -15,6 +15,10 @@ static int validate_of_partition(struct device_node *np, int slot)
>  	int a_cells = of_n_addr_cells(np);
>  	int s_cells = of_n_size_cells(np);
>  
> +	/* Skip nodes without a reg property (e.g. nvmem-layout) */
> +	if (!reg)
> +		return 1;
> +
>  	/* Make sure reg len match the expected addr and size cells */
>  	if (len / sizeof(*reg) != a_cells + s_cells)
>  		return -EINVAL;

[Severity: High]
This is a pre-existing issue, but could malicious device tree properties
cause an integer underflow here?

The functions of_n_addr_cells() and of_n_size_cells() return signed integers.
If a device tree specifies a large unsigned value like 0xffffffff, these
functions will return -1.

The validation check above can be bypassed if the sum of negative and positive
cell counts equals the length ratio.

When the negative size is later passed to of_read_number(reg, a_cells) in
add_of_partition(), the internal while (size--) loop underflows, causing a
massive out-of-bounds read and panic.

[ ... ]

> @@ -97,9 +102,10 @@ int of_partition(struct parsed_partitions *state)
>  			break;
>  		}
>  
> -		add_of_partition(state, slot, np);
> -
> -		slot++;
> +		if (of_property_present(np, "reg")) {
> +			add_of_partition(state, slot, np);

[Severity: High]
This isn't a bug introduced by this patch, but does add_of_partition() have a
NULL pointer dereference risk?

Inside add_of_partition(), partname is populated by checking for "label"
and falling back to "name". If a node omits both properties, of_get_property()
returns NULL:

block/partitions/of.c:add_of_partition() {
    ...
	partname = of_get_property(np, "label", &len);
	if (!partname)
		partname = of_get_property(np, "name", &len);
	strscpy(info->volname, partname, sizeof(info->volname));
    ...
}

Will passing a NULL partname to strscpy() cause a kernel panic?

> +			slot++;
> +		}
>  	}
>  
>  	seq_buf_puts(&state->pp_buf, "\n");

[Severity: High]
This is a pre-existing issue, but does this function leak the partitions_np
device node reference?

A reference is acquired via of_node_get(ddev->of_node) at the start of
of_partition().

If the node is not compatible with "fixed-partitions", the function returns 0
early without calling of_node_put(partitions_np).

Similarly, on this successful parsing path, it returns 1 without releasing
the reference.

Could this lead to memory exhaustion or block the release of dynamically
allocated device nodes every time partitions are rescanned?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260612-block-as-nvmem-v5-0-95e0b30fff90@oss.qualcomm.com?part=1

Re: [PATCH v5 9/9] arm64: dts: qcom: arduino-imola: Describe NVMEM layout for WiFi/BT addresses

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] Confused Deputy / Use-After-Free via dev_t reuse in block NVMEM provider.
--

commit 459b659c960efdc8a9e2177c5bc4f832e7ee5730
Author: Daniel Golle <daniel@makrotopia.org>

block: implement NVMEM provider

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. For now, NVMEM is only
registered for the whole disk block device.

> diff --git a/block/blk-nvmem.c b/block/blk-nvmem.c
> new file mode 100644
> index 0000000000000..c005f059d9fe5
> --- /dev/null
> +++ b/block/blk-nvmem.c
[ ... ]
> +static int blk_nvmem_reg_read(void *priv, unsigned int from, void *val, size_t bytes)
> +{
> +	blk_mode_t mode = BLK_OPEN_READ | BLK_OPEN_RESTRICT_WRITES;
> +	dev_t devt = (dev_t)(uintptr_t)priv;
> +	size_t bytes_left = bytes;
> +	loff_t pos = from;
> +	int ret = 0;
> +
> +	struct file *bdev_file __free(fput) = bdev_file_open_by_dev(devt, mode, priv, NULL);

[Severity: High]
Does this code allow for a cross-device data leak if the block device is
removed and its dev_t is reassigned?

If an NVMEM consumer (such as a WiFi driver or a process holding an open
sysfs file) retains an active reference to the NVMEM cell, the nvmem_device
remains alive even after blk_nvmem_del() calls nvmem_unregister() because
nvmem_unregister() only decrements the registration reference count.

If the block layer then frees the removed device's dev_t, it could be
immediately reassigned to a newly plugged block device (e.g. a USB stick).

If the consumer later reads the NVMEM cell, wouldn't bdev_file_open_by_dev()
successfully open the new device using the reused dev_t, allowing the
consumer to unknowingly read data from the unrelated device?

> +	if (IS_ERR(bdev_file))
> +		return PTR_ERR(bdev_file);
> +
[ ... ]
> +void blk_nvmem_add(struct block_device *bdev)
> +{
> +	struct device *dev = &bdev->bd_device;
> +	struct nvmem_config config = {};
[ ... ]
> +	config.id = NVMEM_DEVID_NONE;
> +	config.dev = dev;
> +	config.name = dev_name(dev);
> +	config.owner = THIS_MODULE;
> +	config.priv = (void *)(uintptr_t)dev->devt;

[Severity: High]
Is it safe to store the dev_t here as the priv pointer?

Since the dev_t identifier can be reassigned by the block layer once the
device is removed, storing it this way might lead to the isolation issue
mentioned above if an NVMEM consumer holds a reference past the device's
removal.

> +	config.reg_read = blk_nvmem_reg_read;
> +	config.size = bdev_nr_bytes(bdev);
> +	config.word_size = 1;

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260612-block-as-nvmem-v5-0-95e0b30fff90@oss.qualcomm.com?part=9