At Display Next Hackfest 2026 we reviewed progress moving brightness control into the DRM connector properties.
There is a range LUMINANCE property that will default to 0->0. Once a driver attaches a backlight it will be updated to 1->max. If the panel supports the minimum backlight turning off the display the range can later be updated to 0->max instead of 1->max. Version 8 had a lot of review feedback, and the biggest change is that this no longer has the legacy sysfs interface for brightness control. There is a Kconfig knob introduced that turns on the new API, and when the new API is available all drivers will conflict with the old backlight control API. This will allow us to land the new brightness control API and the transition to the new API separately. *This series only tracks the new API itself.* The following compositors have implemented matching support, although they need to be changed again for items modified in v10 (the dropped cap): * Kwin: https://invent.kde.org/plasma/kwin/-/merge_requests/9298 * Mutter: https://gitlab.gnome.org/swick/mutter/-/commits/wip/kms-luminance-prop * Wlroots: https://gitlab.freedesktop.org/wlroots/wlroots/-/merge_requests/5384 I've tested this series using modetest on amdgpu. The series is also available on this branch for easy testing. https://git.kernel.org/pub/scm/linux/kernel/git/superm1/linux.git/log/?h=superm1/backlight-property-v11 Signed-off-by: Mario Limonciello <[email protected]> --- Changes in v11: * Rebased on drm-tip (fixes Intel CI failing to apply the KUnit patch) * Squashed the amdgpu KUnit fixture update into the amdgpu luminance patch and moved the bios_scratch_reg_offset fix before it, so every commit builds and passes KUnit * Dropped drm/radeon and drm/gma500 patches: both are non-atomic drivers, so userspace can't use an atomic connector property there (Sashiko) * Restored the unconditional select of BACKLIGHT_CLASS_DEVICE in all migrated drivers, fixing ACPI_VIDEO unmet dependencies and link failures (Sashiko) * Core: don't call .disable_luminance when entering self refresh, and only call .set_luminance when the luminance changes or on a modeset that isn't a self refresh exit (Leo Li, Sashiko) * Drivers on ACPI systems (amdgpu, i915/xe) only attach LUMINANCE when acpi_video_backlight_use_native() allows it, keeping the acpi_video fallback otherwise (Sashiko) * Non-atomic paths (legacy non-DC amdgpu, nouveau NV04 and nouveau.atomic=0) keep the backlight class device (Sashiko) * bridge/panel: removed rebase artifacts from drm_bridge.h/drm_panel.h, fixed an invalid container_of() in the panel bridge, cleaned up the connector on error, and left backlight power to drm_panel_enable()/ drm_panel_disable() (Sashiko) * bridge_connector: dropped .disable_luminance, which clobbered the bridge's saved level * amdgpu: restore brightness after GPU reset and modesets for LUMINANCE panels, and skip programming unchanged values (Leo Li, Sashiko) * amdgpu KUnit: fixed connector_type IDA mismatch (Sashiko) * amdgpu: seed LUMINANCE from the hardware level; left the unrelated privacy screen code in commit_tail unchanged * i915: fall back to the backlight class device if attaching LUMINANCE fails * panel: don't attach LUMINANCE for panel bridges attached after device registration, and update brightness under the backlight ops_lock * ps8622: program the committed luminance in pre_enable * i915: enable the backlight at the committed level, and fix the build with BACKLIGHT_CLASS_DEVICE=n (Sashiko) * nouveau: call the luminance helpers from the NV50 commit tail, attach the property before drm_dev_register(), and fix a stale eDP brightness on the class device path (Sashiko) * gud: apply LUMINANCE within the atomic commit instead of a worker, fixing an endless commit loop, a use-after-free on disconnect and brightness clobbering; attach the property at init (Sashiko) * ps8622: track internal PWM mode explicitly and don't touch I2C while powered down (Sashiko) * ssd130x: register the backlight device only without DRM_LUMINANCE, use the committed contrast on enable, don't clobber it on disable, skip writes while unpowered, and unify contrast dispatch (Sashiko) * Known limitation: with DRM_LUMINANCE, amdgpu ATIF firmware brightness requests are not forwarded (i915 OpRegion ASLE requests are already ignored when native backlight control is in use) * Link to v10: https://lore.kernel.org/dri-devel/20261102-superm1-backlight-property-v10-0-b2a6f2413...@kernel.org/ Changes in v10: * Split patch 7 (panel/bridge connector luminance forwarding) into three separate patches: - drm/bridge: add connector luminance operations - drm/panel: add connector luminance forwarding - drm/bridge_connector: add luminance support * Dropped MIPI-DBI tiny driver migrations and the new mipi_dbi connector luminance helpers (Javier): backlight is always NULL when CONFIG_BACKLIGHT_CLASS_DEVICE is disabled, so these drivers can't support LUMINANCE without DT binding changes or a new CONFIG_BACKLIGHT_SYSFS option. Will revisit later. * Added IS_ENABLED(CONFIG_DRM_LUMINANCE) conditional guards to all individual DRM driver patches that call drm_connector_attach_luminance_property() * Moved the LUMINANCE property patch after the new "Add support for a DRM backlight capability" patch to better separate backlight vs luminance functionality * Link to v9: https://lore.kernel.org/dri-devel/[email protected]/ To: Maxime Ripard <[email protected]> To: Alex Deucher <[email protected]> To: Jani Nikula <[email protected]> To: Javier Martinez Canillas <[email protected]> To: Maarten Lankhorst <[email protected]> To: Thomas Zimmermann <[email protected]> To: David Airlie <[email protected]> To: Simona Vetter <[email protected]> To: Harry Wentland <[email protected]> To: Leo Li <[email protected]> To: Rodrigo Siqueira <[email protected]> Cc: Xaver Hugl <[email protected]> Cc: [email protected] Cc: [email protected] Cc: [email protected] Cc: [email protected] Cc: [email protected] Cc: [email protected] --- Mario Limonciello (11): drm: add connector LUMINANCE property drm/amd/display: Pass up errors reading actual brightness drm/amd: add luminance property support drm/i915/display: add luminance property support drm/bridge: add connector luminance operations drm/panel: add connector luminance forwarding drm/bridge_connector: add luminance support drm/nouveau: add connector luminance support drm/gud: add connector luminance support drm/bridge: add PS8622 connector luminance support drm/solomon: add SSD130x connector luminance support Mario Limonciello (AMD) (1): drm/amdgpu: Check bios_scratch_reg_offset in backlight level helper drivers/gpu/drm/Kconfig | 14 ++ drivers/gpu/drm/amd/amdgpu/amdgpu_atombios.c | 7 +- drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 16 +-- drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.h | 7 + .../amd/display/amdgpu_dm/amdgpu_dm_backlight.c | 91 +++++++++++- .../amd/display/amdgpu_dm/amdgpu_dm_backlight.h | 5 +- .../amd/display/amdgpu_dm/amdgpu_dm_connector.c | 5 +- .../amdgpu_dm/tests/amdgpu_dm_backlight_test.c | 72 ++++++++-- .../amdgpu_dm/tests/amdgpu_dm_kunit_helpers.c | 7 +- drivers/gpu/drm/bridge/parade-ps8622.c | 66 +++++++-- drivers/gpu/drm/display/drm_bridge_connector.c | 39 ++++++ drivers/gpu/drm/drm_atomic_helper.c | 98 ++++++++++++- drivers/gpu/drm/drm_atomic_state_helper.c | 7 + drivers/gpu/drm/drm_atomic_uapi.c | 5 + drivers/gpu/drm/drm_connector.c | 57 ++++++++ drivers/gpu/drm/drm_panel.c | 93 +++++++++++++ drivers/gpu/drm/gud/gud_connector.c | 20 ++- drivers/gpu/drm/i915/display/icl_dsi.c | 1 + drivers/gpu/drm/i915/display/intel_backlight.c | 74 ++++++++-- drivers/gpu/drm/i915/display/intel_backlight.h | 1 + drivers/gpu/drm/i915/display/intel_display.c | 2 + drivers/gpu/drm/i915/display/intel_dp.c | 1 + drivers/gpu/drm/i915/display/intel_lvds.c | 1 + drivers/gpu/drm/i915/display/intel_panel.c | 8 +- drivers/gpu/drm/i915/display/vlv_dsi.c | 1 + drivers/gpu/drm/nouveau/dispnv50/disp.c | 13 +- drivers/gpu/drm/nouveau/nouveau_backlight.c | 152 ++++++++++++++++++--- drivers/gpu/drm/nouveau/nouveau_connector.c | 3 + drivers/gpu/drm/nouveau/nouveau_connector.h | 23 ++++ drivers/gpu/drm/nouveau/nouveau_drm.c | 6 + drivers/gpu/drm/solomon/ssd130x.c | 149 +++++++++++++------- drivers/gpu/drm/solomon/ssd130x.h | 2 + drivers/gpu/drm/tests/drm_connector_test.c | 28 ++++ include/drm/drm_atomic_helper.h | 3 + include/drm/drm_bridge.h | 20 +++ include/drm/drm_connector.h | 16 +++ include/drm/drm_modeset_helper_vtables.h | 28 ++++ include/drm/drm_panel.h | 4 + 38 files changed, 1008 insertions(+), 137 deletions(-) --- base-commit: 9f54e1a5b50dc017d371c435b12ddb5300c7d5b2 change-id: 20261101-superm1-backlight-property-1ee9b1a4b24d Best regards, -- Mario Limonciello <[email protected]>
