Re: [PATCH v3 0/8] Add support for a DRM backlight capability

[Mario Limonciello <mario.limonciello@amd.com>]

On 5/4/26 08:55, Louis Chauvet wrote:
> [You don't often get email from louis.chauvet@bootlin.com. Learn why 
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> 
> On 4/25/26 00:09, Mario Limonciello wrote:
>> From: Mario Limonciello (AMD) <superm1@kernel.org>
>>
>> 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-v3
> 
> Hello,
> 
> thanks for this work, I am very interested in this progress so I can
> help you to test / implement more features.

Thanks!  I have a few other series I'm juggling in other subsystems, but 
will try to get another spin this cycle.

> 
> I think you forgot to include the revert of "backlight: Remove notifier"
> in your series, it can't be applied without it.
> 

Yes - thanks for catching this.  It's on my tree at 
https://git.kernel.org/pub/scm/linux/kernel/git/superm1/linux.git/log/?h=superm1/backlight-property-v3 
but I forgot it when I built the series to get that one.

> I will take a look and see if I can create a VKMS implementation of your
> work.

Cool!  Please take a look at the IGT patches I did too if you didn't see 
them.  This should hopefully work once you glue it to VKMS.

https://lore.kernel.org/dri-devel/20260424221021.167179-1-mario.limonciello@amd.com/

> 
> Thanks for this work,
> 
>> David Rheinsberg (1):
>>    backlight: add kernel-internal backlight API
>>
>> Mario Limonciello (6):
>>    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
>>
>> Marta Lofstedt (1):
>>    backlight: expose the current brightness in the new kernel API
>>
>>   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 |  88 +++-
>>   drivers/gpu/drm/drm_atomic_uapi.c             |  24 ++
>>   drivers/gpu/drm/drm_backlight.c               | 406 ++++++++++++++++++
>>   drivers/gpu/drm/drm_connector.c               |  12 +
>>   drivers/gpu/drm/drm_drv.c                     |   8 +
>>   drivers/gpu/drm/drm_ioctl.c                   |  10 +
>>   drivers/gpu/drm/drm_mode_config.c             |   7 +
>>   drivers/gpu/drm/drm_mode_object.c             |  66 ++-
>>   drivers/gpu/drm/drm_sysfs.c                   |  54 +++
>>   drivers/video/backlight/backlight.c           |  83 ++++
>>   include/drm/drm_backlight.h                   |  45 ++
>>   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                     |  30 ++
>>   include/uapi/drm/drm.h                        |  10 +
>>   20 files changed, 852 insertions(+), 23 deletions(-)
>>   create mode 100644 drivers/gpu/drm/drm_backlight.c
>>   create mode 100644 include/drm/drm_backlight.h
>>
>