> Subject: RE: [PATCH v3 1/8] drm/i915/backlight: Use default/max brightness for
> VESA AUX backlight init
>
> On Wed, 25 Feb 2026, "Kandpal, Suraj" <[email protected]> wrote:
> >> Subject: Re: [PATCH v3 1/8] drm/i915/backlight: Use default/max
> >> brightness for VESA AUX backlight init
> >>
> >> On Tue, 24 Feb 2026, Suraj Kandpal <[email protected]> wrote:
> >> > If the brightness fetched from VBT/previous state is 0 on backlight
> >> > initialization, then set the brightness to a default/max value.
> >> > Whenever the minimum brightness is reported as 0 there are chances
> >> > we end up with blank screen. This confuses the user into thinking
> >> > the display is acting weird. This occurs in eDP 1.5 when we are
> >> > using PANEL_LUMINANCE_OVERRIDE mode to mainpulate brightness via
> >> > luminance values.
> >> >
> >> > Closes:
> >> > https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/15671
> >> > Signed-off-by: Suraj Kandpal <[email protected]>
> >> > Reviewed-by: Arun R Murthy <[email protected]>
> >> > ---
> >> > v1 -> v2:
> >> > - Let users set brightness to 0, make it so that it's just not done
> >> > by default (Arun)
> >> >
> >> > v2 -> v3:
> >> > -Update commit header and message (Arun)
> >> >
> >> > drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c | 4 ++++
> >> > 1 file changed, 4 insertions(+)
> >> >
> >> > diff --git a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> >> > b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> >> > index eb05ef4bd9f6..c40ce310ad97 100644
> >> > --- a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> >> > +++ b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> >> > @@ -564,6 +564,8 @@ static int
> >> > intel_dp_aux_vesa_setup_backlight(struct
> >> intel_connector *connector,
> >> > }
> >> > panel->backlight.level =
> >> intel_dp_aux_vesa_get_backlight(connector, 0);
> >> > panel->backlight.enabled = panel->backlight.level != 0;
> >> > + if (!panel->backlight.level)
> >> > + panel->backlight.level = panel->backlight.max;
> >>
> >> How does this help when .enabled is still based on level != 0 above?
> >>
> >
> > Well we keep the backlight.enabled as false if we read a 0 back from the
> > DPCD
> or the current level state is 0.
> > This is to maintain the policy that if during setup we get 0 as
> > backlight value eDP backlight is currently disabled (which means
> > __intel_backlight_enable needs be called). We then change the current
> > level to max so that when backlight enable is called after setup from
> intel_backlight_update, we enable backlight with max level so that we do not
> end up with a blank screen. This is also where we set backlight.enabled =
> true.
> > This is to tackle different eDP behavior where, some preserve the
> > last brightness value programmed in them (in that case users want the
> > same brightness to continue) while others don't and just 0 it out instead of
> having some default value (in that case we keep backlight.enabled = false
> later
> to be made true during the __intel_backlight_enable call).
> > We face these scenarios in some compositors during the pass key phase
> > where the compositor is still totally not doing everything and does not send
> us any explicit brightness value to set thinking eDP would have some basic
> default value of it's own . We end up getting a 0 from DPCD and we enable and
> set the backlight enable with 0 value which anyways later causes us to call
> backlight disable.
> > In this case during authentication in some compositors like Fedora
> > there are cases where we do not get a explicitly backlight value till the
> > user
> has to blindly enter their Passkey, after which the compositor sends us some
> sane value which we then program.
>
> There's a long history of problems with the PWM backlight unexpectedly going
> from 0 to max.
Right but at least with this now luminance values will continue if DPCD
maintains its state if we get a value back, otherwise we set a
Default value.
Can we proceed with getting this merged ? Would really help the user.
Regards,
Suraj Kandpal
>
> BR,
> Jani.
>
> >
> > Regards,
> > Suraj Kandpal
> >
> >> > drm_dbg_kms(display->drm,
> >> > "[CONNECTOR:%d:%s] AUX VESA Nits backlight
> >> > level
> >> is controlled through DPCD\n",
> >> > connector->base.base.id,
> >> > connector->base.name);
> >> @@ -573,6
> >> > +575,8 @@ static int intel_dp_aux_vesa_setup_backlight(struct
> >> intel_connector *connector,
> >> > if (current_mode ==
> >> DP_EDP_BACKLIGHT_CONTROL_MODE_DPCD) {
> >> > panel->backlight.level = current_level;
> >> > panel->backlight.enabled =
> >> > panel->backlight.level != 0;
> >> > + if (!panel->backlight.level)
> >> > + panel->backlight.level =
> >> > panel->backlight.max;
> >>
> >> Ditto.
> >>
> >> > } else {
> >> > panel->backlight.level = panel->backlight.max;
> >> > panel->backlight.enabled = false;
> >>
> >> --
> >> Jani Nikula, Intel
>
> --
> Jani Nikula, Intel
