We fix this by writing the brightness value to efivar 'backlight-level'
at shutdown only, when it is changed since the last boot.

Changes in v3:
- Fixed a bug, in which apple_brightness_shutdown is still called on
   non-supported devices.
Changes in v2:
- Saved the brightness only when it is different than the previous boot.

Link to v2:
https://lore.kernel.org/all/20260315215302.24087-1-atharvatiwarilinuxdev@gmail.com/
Link to v1:
https://lore.kernel.org/all/20260206125641.12983-1-atharvatiwarilinuxdev@gmail.com/

Atharva Tiwari (2):
  efi: Save Brightness using EFI on Macs
  platform/apple-gmux: use apple_brightness to save brightness to EFI

 drivers/firmware/efi/Kconfig                  | 10 +++
 drivers/firmware/efi/Makefile                 |  1 +
 drivers/firmware/efi/apple-brightness.c       | 67 +++++++++++++++++++
 drivers/platform/x86/apple-gmux.c             | 21 ++++++
 .../linux/platform_data/apple-brightness.h    | 20 ++++++
 5 files changed, 119 insertions(+)
 create mode 100644 drivers/firmware/efi/apple-brightness.c
 create mode 100644 include/linux/platform_data/apple-brightness.h

-- 
2.43.0