Re: [PATCH v8 04/14] drm: add connector backlight (LUMINANCE) infrastructure

[Maxime Ripard <mripard@kernel.org>]

[-- Attachment #1: Type: text/plain, Size: 1849 bytes --]

On Thu, Oct 01, 2026 at 03:12:25PM -0400, Harry Wentland wrote:
> On 2026-09-08 00:40, Mario Limonciello wrote:
> > Backlight brightness is a property of a display, and thus of a DRM
> > connector, yet it has historically only been controllable through the
> > separate backlight sysfs interface. Add a generic, backend-agnostic
> > per-connector LUMINANCE range property so brightness can be driven
> > through the atomic modeset path like any other connector state.
> > 
> > A struct drm_backlight is embedded in every connector and initialized by
> > the core; drivers do not allocate it. A driver links a backend (today a
> > backlight_device, in the future DDC/CI, MIPI-DCS, ...) with
> > drm_backlight_link(), which creates the connector's LUMINANCE property
> 
> I didn't follow the whole discussion so I'm curious why we decided to
> name this LUMINANCE. I think of nits or cd/m^2 when I hear luminance.
> I think it's dangerous when we use for a property that is currently
> not able to describe the output in nits. You would also then have to
> define whether you're dealing with a fully white screen, or parts that
> are white. In short, you're ending up in color management territory where
> these things have specific meanings and it's easy to get it wrong if
> we don't define the nuances right.
> 
> Why not simply call it BACKLIGHT, which is what it is? Later, if we then
> add support for luminance (in absolute nits) we can use the LUMINANCE
> term for that. Otherwise it'll be lost to us and be apt to confuse
> people.
> 
> I'm on the fence about calling it "drm brightness", as suggested by Jani,
> but could get onboard with something like PANEL_BRIGHTNESS.

I don't think we should mention panel here, it will be useful for at
least HDMI and DP too.

brightness works for me though

Maxime

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 273 bytes --]