drm/amd/display: workaround for oled eDP not lighting up on DCN401

[Why]
Currently there's an issue on DCN401 that prevents oled eDP panels from
being lit up that is still under investigation. To unblock dev work
while investigating, we can work around the issue by skipping toggling
the enablement of the backlight.

[How]
 - new debug bit that will skip touching backlight enable DPCD for oled
Reviewed-by: Alvin Lee <alvin.lee2@amd.com>
Reviewed-by: Wenjing Liu <wenjing.liu@amd.com>
Acked-by: Zaeem Mohamed <zaeem.mohamed@amd.com>
Signed-off-by: Joshua Aberback <joshua.aberback@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/dc.h

@@ -1042,6 +1042,7 @@ struct dc_debug_options {
 	unsigned int force_easf;
 	unsigned int force_sharpness;
 	unsigned int force_lls;
+	bool edp_oled_no_backlight_enable;
 };
 
 

drivers/gpu/drm/amd/display/dc/link/protocols/link_edp_panel_control.c

@@ -248,6 +248,9 @@ bool edp_backlight_enable_aux(struct dc_link *link, bool enable)
 		link->connector_signal != SIGNAL_TYPE_DISPLAY_PORT))
 		return false;
 
+	if (link->dc->debug.edp_oled_no_backlight_enable && link->dpcd_sink_ext_caps.bits.oled)
+		return true;
+
 	if (core_link_write_dpcd(link, DP_SOURCE_BACKLIGHT_ENABLE,
 		&backlight_enable, 1) != DC_OK)
 		return false;

drivers/gpu/drm/amd/display/dc/resource/dcn401/dcn401_resource.c

@@ -732,6 +732,7 @@ static const struct dc_debug_options debug_defaults_drv = {
 	},
 	.force_cositing = CHROMA_COSITING_TOPLEFT + 1,
 	.disable_idle_power_optimizations = true,
+	.edp_oled_no_backlight_enable = true,
 };
 
 static struct dce_aux *dcn401_aux_engine_create(