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

[Jani Nikula]

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.

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