[v5,0/4] block: preparations for NVMEM provider

Message

Daniel Golle July 30, 2024, 7:24 p.m. UTC

On embedded devices using an eMMC it is common that one or more (hw/sw)
partitions on the eMMC are used to store MAC addresses and Wi-Fi
calibration EEPROM data.

Typically the NVMEM framework is used to have kernel drivers read and
use binary data from EEPROMs, efuses, flash memory (MTD), ...

Using references to NVMEM bits in Device Tree allows the kernel to
access and apply e.g. the Ethernet MAC address, which can be a requirement
for userland to come up (e.g. for nfsroot).

The aim of this series is to prepare the block subsystem to allow for
the implementation of an NVMEM provider similar to other types of
non-volatile storage, so the same approach already used for EEPROMs, MTD
(raw flashes) and UBI-managed NAND can also be used for devices storing
those bits on an eMMC.

Define a device tree schema for block devices and partitions on them,
which (similar to how it now works also for UBI volumes) can be matched
by one or more properties (partition UUID, partition name and/or
partition number). Implement matching code to attach firmware nodes to
partitions based on that, so they can be referenced in DT and used as
NVMEM providers rather than just the block device as a whole.

Also add a simple notification API for other subsystems to be notified
about additions and removals of block devices, which is going to be used
by the block-backed NVMEM provider. Being an optional feature it is easy
for users not needing this feature to still build the kernel without
any functional changes (simply by not selecting CONFIG_BLOCK_NOTIFIERS,
which is disabled by default).

The actual NVMEM provider module which builds upon the block notification
interface is not included in this series yet, as it isn't touching any
block subsystem internals it will be sent separately once this series is
accepted. In the meantime, you can find it in previous iterations of
this series where it was still included.

The overall goal is uniform handling of things like MAC addresses and
WiFi calibration data across practially all flash storage types used for
this purpose (MTD, UBI, and soon also MMC or and in future maybe also
other block devices) on embedded devices.
---
Changes since v4 sent on Jun 27th, cosmetics
 - make sure multiline comments do not exceed 80 columns

Changes since v3 sent on Jun 26th, addressing comments from Jens Axboe:
 - improve readability and error-handling in fwnode-matching code
 - remove forgotten code from earlier development accessing ddev->parent
 - use '#if defined' instead of '#ifdef' in header
 - provide inline dummies in case of CONFIG_BLOCK_NOTIFIERS not being set

Changes since v2 sent on May 30th 2024 [1] addressing comments from
Hauke Mehrtens (https://patchwork.kernel.org/comment/25892133/)
 - Check length of UUID and PARTNAME.
 - Remove forgotten fallback to get 'partitions' subnode from parent.
   It is no longer needed and was a left over from earlier development.
 - Split series into 3 parts, one for each affected subsystem. This is
   the first part covering only the changes needed in the block
   subsystem. The second part adds the actual nvmem provider to
   drivers/nvmem/, the third part is going to make use of it for MMC
   block devices and cover changes in drivers/mmc.

Changes since v1 sent on March 21st 2024 [2]:
 - introduce notifications for block device addition and removal for
   in-kernel users. This allows the nvmem driver to be built as a module
   and avoids using class_interface and block subsystem internals as
   suggested in https://patchwork.kernel.org/comment/25771998/ and
   https://patchwork.kernel.org/comment/25770441/

This series has previously been submitted as RFC on July 19th 2023[3]
and most of the basic idea did not change since. Another round of RFC
was submitted on March 5th 2024[4].

[1]: https://patchwork.kernel.org/project/linux-block/list/?series=857192
[2]: https://patchwork.kernel.org/project/linux-block/list/?series=837150&archive=both
[3]: https://patchwork.kernel.org/project/linux-block/list/?series=767565
[4]: https://patchwork.kernel.org/project/linux-block/list/?series=832705

Daniel Golle (4):
  dt-bindings: block: add basic bindings for block devices
  block: partitions: populate fwnode
  block: add support for notifications
  block: add new genhd flag GENHD_FL_NVMEM

 .../bindings/block/block-device.yaml          | 22 +++++
 .../devicetree/bindings/block/partition.yaml  | 51 +++++++++++
 .../devicetree/bindings/block/partitions.yaml | 20 +++++
 block/Kconfig                                 |  6 ++
 block/Makefile                                |  1 +
 block/blk-notify.c                            | 87 +++++++++++++++++++
 block/partitions/core.c                       | 72 +++++++++++++++
 include/linux/blkdev.h                        | 13 +++
 8 files changed, 272 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/block/block-device.yaml
 create mode 100644 Documentation/devicetree/bindings/block/partition.yaml
 create mode 100644 Documentation/devicetree/bindings/block/partitions.yaml
 create mode 100644 block/blk-notify.c