[PATCH v3 1/8] drm/i915/backlight: Use default/max brightness for VESA AUX backlight init

[Suraj Kandpal <suraj.kandpal@intel.com>]

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 <suraj.kandpal@intel.com>
Reviewed-by: Arun R Murthy <arun.r.murthy@intel.com>
---
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;
 		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;
 		} else {
 			panel->backlight.level = panel->backlight.max;
 			panel->backlight.enabled = false;
-- 
2.34.1