[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@xxxxxxxxxxxxxx/

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@xxxxxxxxxxxxxxxx>
---
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@xxxxxxxxxxxxxxxx

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

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@xxxxxxxxxxxxxxxx

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@xxxxxxxxxxxxxxxx

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@xxxxxxxxxxxxxxxx

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@xxxxxxxxxxxxxxxx

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@xxxxxxxxxxxxxxxx

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@xxxxxxxxxxxxxxxx

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@xxxxxxxxxxxxxxxx

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@xxxxxxxxxxxxxxxx/
- 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@xxxxxxxxxxxxxxxx

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@xxxxxxxxxxxxxxxx

---
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@xxxxxxxxxxxxxxxx>