From: "Theo de Raadt" <deraadt@openbsd.org>
Subject: Re: sys/qcdpc: blank eDP panels during suspend
To: tech@openbsd.org
Date: Sun, 04 Oct 2026 19:26:18 -0600

Theo de Raadt <deraadt@openbsd.org> wrote:

> > +int
> > +qcdpc_activate(struct device *self, int act)
> > +{
> > +	struct qcdpc_softc *sc = (struct qcdpc_softc *)self;
> > +	int ret;
> > +
> > +	if (sc != qcdpc_bl || !sc->sc_bl.aux_enable)
> > +		return config_activate_children(self, act);
> > +
> > +	switch (act) {
> > +	case DVACT_QUIESCE:
> > +		ret = config_activate_children(self, act);
> > +		if (ret)
> > +			return ret;
> > +
> > +		if (!sc->sc_bl_suspended) {
> > +			ret = drm_dp_dpcd_read_byte(&sc->sc_aux,
> > +			    DP_EDP_DISPLAY_CONTROL_REGISTER, &sc->sc_bl_control);
> > +			if (ret < 0)
> > +				return ret;
> > +			sc->sc_bl_suspended = 1;
> > +		}
> > +
> > +		return drm_dp_dpcd_write_byte(&sc->sc_aux,
> > +		    DP_EDP_DISPLAY_CONTROL_REGISTER,
> > +		    (sc->sc_bl_control & ~DP_EDP_BACKLIGHT_ENABLE) |
> > +		    DP_EDP_BLACK_VIDEO_ENABLE);

From a style perspective, will this work?

Regarding this, why are you inspecting "sc != qcdpc_bl"?

   	 if (sc != qcdpc_bl || !sc->sc_bl.aux_enable)

You are running code in this activate function because that is
already true.

Index: qcdpc.c
===================================================================
RCS file: /cvs/src/sys/dev/fdt/qcdpc.c,v
diff -u -p -u -r1.2 qcdpc.c
--- qcdpc.c	9 Mar 2026 23:57:53 -0000	1.2
+++ qcdpc.c	5 Oct 2026 01:12:04 -0000
+int
+qcdpc_activate(struct device *self, int act)
+{
+	struct qcdpc_softc *sc = (struct qcdpc_softc *)self;
+	int ret;
+
+	switch (act) {
+	case DVACT_QUIESCE:
+		ret = config_activate_children(self, act);
+		if (ret)
+			return ret;
+		if (sc != qcdpc_bl || !sc->sc_bl.aux_enable)
+			break;
+
+		if (!sc->sc_bl_suspended) {
+			if (drm_dp_dpcd_read_byte(&sc->sc_aux,
+			    DP_EDP_DISPLAY_CONTROL_REGISTER,
+			    &sc->sc_bl_control) < 0)
+				break;
+			sc->sc_bl_suspended = 1;
+		}
+		(void) drm_dp_dpcd_write_byte(&sc->sc_aux,
+		    DP_EDP_DISPLAY_CONTROL_REGISTER,
+		    (sc->sc_bl_control & ~DP_EDP_BACKLIGHT_ENABLE) |
+		    DP_EDP_BLACK_VIDEO_ENABLE);
+		break;
+	case DVACT_WAKEUP:
+		if (sc->sc_bl_suspended) {
+			if (drm_dp_dpcd_write_byte(&sc->sc_aux,
+			    DP_EDP_DISPLAY_CONTROL_REGISTER,
+			    sc->sc_bl_control) == 0)
+				sc->sc_bl_suspended = 0;
+		}
+		return config_activate_children(self, act);
+	default:
+		return config_activate_children(self, act);
 	}
 }