[Intel-gfx] [PATCH] drm/i915/dp: add a delay before setting panel brightness after power on

[Vasily Khoruzhick]

On Tue, Sep 14, 2021 at 3:31 PM Jani Nikula <jani.nikula at linux.intel.com> wrote:
>
> On Tue, 14 Sep 2021, Lyude Paul <lyude at redhat.com> wrote:
> > On Tue, 2021-09-14 at 12:09 +0300, Jani Nikula wrote:
> >> On Mon, 13 Sep 2021, Vasily Khoruzhick <anarsoul at gmail.com> wrote:
> >> > Panel in my Dell XPS 7590, that uses Intel's HDR backlight interface to
> >> > control brightness, apparently needs a delay before setting brightness
> >> > after power on. Without this delay the panel does accept the setting
> >> > and may come up with some arbitrary brightness (sometimes it's too dark,
> >> > sometimes it's too bright, I wasn't able to find a system).
> >> >
> >> > I don't have access to the spec, so I'm not sure if it's expected
> >> > behavior or a quirk for particular device.
> >> >
> >> > Delay was chosen by experiment: it works with 100ms, but fails with
> >> > anything lower than 75ms.
> >>
> >> Looks like we don't respect the panel delays for DPCD backlight. The
> >> values are used for setting up the panel power sequencer, and thus PWM
> >> based backlight, but we should probably use the delays in DPCD backlight
> >> code too.
> >
> > This makes sense to me, you're referring to the panel delays in the VBT
> > correct?
>
> Yes. See pps_init_delays() and intel_pps_backlight_on(). The delays
> aren't applied to DPCD backlight, I think it would make sense if they
> were.

I guess it explains why it usually stops working after suspend.
Probably BIOS doesn't re-init the power sequencer on resume.

> BR,
> Jani.
>
> >
> >>
> >> BR,
> >> Jani.
> >>
> >>
> >> >
> >> > Signed-off-by: Vasily Khoruzhick <anarsoul at gmail.com>
> >> > ---
> >> >  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 4f8337c7fd2e..c4f35e1b5870 100644
> >> > --- a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> >> > +++ b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> >> > @@ -210,6 +210,10 @@ intel_dp_aux_hdr_enable_backlight(const struct
> >> > intel_crtc_state *crtc_state,
> >> >
> >> >         ctrl = old_ctrl;
> >> >         if (panel->backlight.edp.intel.sdr_uses_aux) {
> >> > +               /* Wait 100ms to ensure that panel is ready otherwise it
> >> > may not
> >> > +                * set chosen backlight level
> >> > +                */
> >> > +               msleep(100);
> >> >                 ctrl |= INTEL_EDP_HDR_TCON_BRIGHTNESS_AUX_ENABLE;
> >> >                 intel_dp_aux_hdr_set_aux_backlight(conn_state, level);
> >> >         } else {
> >>
>
> --
> Jani Nikula, Intel Open Source Graphics Center