On Tue, 14 Sep 2021, Vasily Khoruzhick <anarsoul@xxxxxxxxx> wrote: > On Tue, Sep 14, 2021 at 3:31 PM Jani Nikula <jani.nikula@xxxxxxxxxxxxxxx> wrote: >> >> On Tue, 14 Sep 2021, Lyude Paul <lyude@xxxxxxxxxx> wrote: >> > On Tue, 2021-09-14 at 12:09 +0300, Jani Nikula wrote: >> >> On Mon, 13 Sep 2021, Vasily Khoruzhick <anarsoul@xxxxxxxxx> 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. The point is, the DPCD backlight isn't driven via the power sequencer, while the PWM pin would be. Please file a bug at [1], and attach /sys/kernel/debug/dri/0/i915_vbt as well as dmesg from boot with drm.debug=14 module parameter set. Thanks, Jani. [1] https://gitlab.freedesktop.org/drm/intel/issues/new > >> BR, >> Jani. >> >> > >> >> >> >> BR, >> >> Jani. >> >> >> >> >> >> > >> >> > Signed-off-by: Vasily Khoruzhick <anarsoul@xxxxxxxxx> >> >> > --- >> >> > 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 -- Jani Nikula, Intel Open Source Graphics Center
