在 2026-06-11四的 13:45 +0800，Pengyu Luo写道：
> On Thu, Jun 11, 2026 at 1:36 PM Icenowy Zheng
> <[email protected]> wrote:
> >
> > 在 2026-06-11四的 13:26 +0800，Pengyu Luo写道：
> > > On Tue, 09 Jun 2026 00:26:20 +0800, Icenowy Zheng
> > > <[email protected]> wrote:
> > > > When the backlight is managed by the panel controller IC, an
> > > > external
> > > > power rail might be powering the backlight.
> > > >
> > > > Add an optional `bl-supply` property to describe such power
> > > > rail,
> > > > thus
> > > > allow disabling the backlight.
> > > >
> > >
> > > Please add it as a hwen pin, this will simplify your code later.
> >
> > I am not sure whether this should be a pin or a regulator -- the DT
> > binding should reflect the HW fact, and LCD panel backlights
> > usually
> > require a high voltage (or even a current source) that is driven by
> > a
> > dedicated regulator.
> >
>
> Most backlight ICs use a hwen pin to enable the supply, afaik, like
> ktz8866, ktz8868, aw99706, etc. We don't touch the VIN. (My
> disclaimer:
> I am just an amateur, know less about the circuit)
I found some specificiation of a LCD panel using DCS brightness to
control backlight at [1] (this panel is supported by panel-himax-
hx83102 driver), and it has no HWEN pins -- the pins related to
backlight seem to be LED_{C2,C1,A} and PWM, which means a backlight
regulator must be present.
Although the situation is a little odd -- the regulator isn't a fixed
one, but a adjustable one adjusted by the panel.
Thanks,
Icenowy
[1]
https://www.scribd.com/presentation/759684395/Titan20-TP-LCM-SPEC-XT2073-Motorola-one-fusion
>
> Best wishes,
> Pengyu
>
> > Thanks,
> > Icenowy
> >
> > >
> > > >
> > > >
> > > > diff --git
> > > > a/Documentation/devicetree/bindings/display/panel/himax,hx83121
> > > > a.ya
> > > > ml
> > > > b/Documentation/devicetree/bindings/display/panel/himax,hx83121
> > > > a.ya
> > > > ml
> > > > index e067a2f6d0b2..aeca3c9a599c 100644
> > > > ---
> > > > a/Documentation/devicetree/bindings/display/panel/himax,hx83121
> > > > a.ya
> > > > ml
> > > > +++
> > > > b/Documentation/devicetree/bindings/display/panel/himax,hx83121
> > > > a.ya
> > > > ml
> > > > @@ -40,6 +40,9 @@ properties:
> > > > vddi-supply:
> > > > description: power supply for IC
> > > >
> > > > + bl-supply:
> > > > + description: power supply for backlight, in case it's
> > > > managed
> > > > via DSC
> > > > +
> > >
> > > s/DSC/DCS/
> > >
> > > Best wishes,
> > > Pengyu
> >
