I have a DCE3 (RS880) and a monitor which supports RGB quantisation.

before executing the EDID test the values are 

radeon_encoder->output_csc = RADEON_OUTPUT_CSC_BYPASS
frame.quantization_range = HDMI_QUANTIZATION_RANGE_DEFAULT

then it executes the EDID test    

if (drm_rgb_quant_range_selectable(radeon_connector_edid(connector))) {
   if (radeon_encoder->output_csc == RADEON_OUTPUT_CSC_TVRGB)
      frame.quantization_range = HDMI_QUANTIZATION_RANGE_LIMITED;
   else
      frame.quantization_range = HDMI_QUANTIZATION_RANGE_FULL;                  
} else {
   frame.quantization_range = HDMI_QUANTIZATION_RANGE_DEFAULT;
}

and the monitor loses sync and displays a blank screen.

Should the code test both the EDID and output_csc != BYPASS before attempting
the range change?