At Display Next Hackfest 2025 we discussed the renewed need for moving brightness control into the DRM connector properties. I've taken the previous efforts from David and Marta, rebased and adjusted for the current kernel.
The legacy sysfs interface is synchronized with the DRM connector (although the scale may be different as DRM connector property is u16). Later after this has been adopted by enough userspace, it may make sense to configure the legacy sysfs interface to be configurable so that only DRM master controls backlight. I've done a first implementation with amdgpu with eDP connectors; but conceivably this can be extended to other connectors like DP for displays that can be controlled via DDC as well later. I have also used DRM review prompts to review this series and fix some bugs which were caught with two different Claude models. The fixes are squashed into the patches. Assisted-by: Claude Opus Assisted-by: Claude Sonnet For ease of testing; this series is also available on this branch: https://git.kernel.org/pub/scm/linux/kernel/git/superm1/linux.git/log/?h=superm1/backlight-property-v4 --- v3->v4: * Address feedback on mailing list for linking, bridge connector handling * Make DRM capability block with writes * Drop unnecessary code Mario Limonciello (AMD) (9): Revert "backlight: Remove notifier" backlight: add kernel-internal backlight API drm: link connectors to backlight devices DRM: Add support for client and driver indicating support for luminance drm/amd/display: Pass up errors reading actual brightness drm/amd: Indicate driver supports luminance drm/amd/display: Allow backlight registration to fail drm/amd/display: use drm backlight drm/bridge: auto-link panel backlight in bridge connector drivers/gpu/drm/Kconfig | 1 + drivers/gpu/drm/Makefile | 2 + drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c | 1 + .../gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 77 ++- drivers/gpu/drm/bridge/panel.c | 15 + .../gpu/drm/display/drm_bridge_connector.c | 15 +- drivers/gpu/drm/drm_atomic_helper.c | 9 + drivers/gpu/drm/drm_atomic_uapi.c | 59 ++- drivers/gpu/drm/drm_backlight.c | 467 ++++++++++++++++++ drivers/gpu/drm/drm_connector.c | 12 + drivers/gpu/drm/drm_drv.c | 8 + drivers/gpu/drm/drm_file.c | 5 + drivers/gpu/drm/drm_ioctl.c | 17 + drivers/gpu/drm/drm_mode_config.c | 7 + drivers/gpu/drm/drm_mode_object.c | 66 ++- drivers/gpu/drm/drm_sysfs.c | 28 +- drivers/video/backlight/backlight.c | 99 ++++ include/drm/drm_backlight.h | 51 ++ include/drm/drm_bridge.h | 1 + include/drm/drm_connector.h | 8 + include/drm/drm_drv.h | 7 + include/drm/drm_file.h | 8 + include/drm/drm_mode_config.h | 5 + include/linux/backlight.h | 56 +++ include/uapi/drm/drm.h | 10 + 25 files changed, 1005 insertions(+), 29 deletions(-) create mode 100644 drivers/gpu/drm/drm_backlight.c create mode 100644 include/drm/drm_backlight.h -- 2.54.0
