[PATCH RFC 0/5] nvmem: Add a UEFI variable backed NVMEM provider

[Abel Vesa]

This is an RFC: I do not expect it to be merged as-is, it is sent to get
feedback on the approach.

Some values a platform needs (for example the WLAN and Bluetooth MAC
addresses on the Qualcomm laptops) are not always available to the kernel
in a convenient form. They may live in firmware-owned SPI-NOR storage
(e.g. a DPP partition) for which there is no straightforward, universally
working way to read them from the non-secure world.

As an alternative, this series allows such values to be provisioned once
into a UEFI variable and consumed in the kernel. It adds a generic NVMEM
provider that exposes the contents of a UEFI variable as an NVMEM device,
so the data can be consumed through the standard nvmem-cells bindings.
MAC addresses are just the motivating use case; the provider itself is
generic.

The first two patches are the actual proposal:

  - dt-bindings: nvmem: Add UEFI variable NVMEM provider
  - nvmem: Add UEFI variable NVMEM provider

The remaining three patches are included only to illustrate how a
consumer would use the provider; they are not meant for merging as part
of this series:

  - Bluetooth: hci_qca: consume a "bd-address" nvmem cell
  - wifi: ath12k: consume a "mac-address" cell
  - arm64: dts: qcom: glymur-crd: wire both to a "MacAddresses" variable

glymur-crd is used here only as a convenient example for the consumer
patches.

Feedback on the provider, and on whether sourcing such values from a UEFI
variable is a reasonable approach when they cannot be read from the
SPI-NOR directly, is very welcome.

Assisted-by: LLM
Signed-off-by: Abel Vesa <abel.vesa at oss.qualcomm.com>
---
Abel Vesa (5):
      dt-bindings: nvmem: Add UEFI variable NVMEM provider
      nvmem: Add UEFI variable NVMEM provider
      Bluetooth: hci_qca: Support BD address from an nvmem cell
      wifi: ath12k: Support MAC address from the firmware node
      arm64: dts: qcom: glymur-crd: Source MAC addresses from a UEFI variable

 .../devicetree/bindings/nvmem/nvmem-efivar.yaml    |  73 ++++++
 arch/arm64/boot/dts/qcom/glymur-crd.dtsi           |  22 ++
 drivers/bluetooth/hci_qca.c                        |  48 ++++
 drivers/net/wireless/ath/ath12k/mac.c              |  14 +-
 drivers/nvmem/Kconfig                              |  12 +
 drivers/nvmem/Makefile                             |   2 +
 drivers/nvmem/efivar.c                             | 273 +++++++++++++++++++++
 7 files changed, 443 insertions(+), 1 deletion(-)
---
base-commit: 1fffefb00cc0b0da1f2ae24e3d33364530ea6515
change-id: 20261014-b4-nvmem-efivar-fec3cab05755

Best regards,
--  
Abel Vesa <abel.vesa at oss.qualcomm.com>