drm/i915/dp: Make the RGB fallback for "4:2:0 only" modes the last resort

Currently we take the Hail Mary RGB fallback for "4:2:0 only" modes
already during the first pass when respect_downstream_limits==true.
It seems better to try everything else first (like ignoring TMDS
clock limits) while still preferring 4:2:0, and only if everything
else has failed fall back to RGB.

Cc: Nicolas Frattaroli <nicolas.frattaroli@collabora.com>
Reviewed-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patch.msgid.link/20260409101539.22032-10-ville.syrjala@linux.intel.com
Tested-by: Nicolas Frattaroli <nicolas.frattaroli@collabora.com>

diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
index 945994fe681ba3b0b533a4864a2e51d1e5978fc5..35b8fb5740aaac4b79d8ec6587f6bcd3f435c89c 100644 (file)
--- a/drivers/gpu/drm/i915/display/intel_dp.c
+++ b/drivers/gpu/drm/i915/display/intel_dp.c
@@ -3410,7 +3410,7 @@ intel_dp_compute_formats(struct intel_encoder *encoder,
                                                     respect_downstream_limits,
                                                     INTEL_OUTPUT_FORMAT_YCBCR420);
 
-               if (ret) {
+               if (ret && !respect_downstream_limits) {
                        drm_dbg_kms(display->drm,
                                    "YCbCr 4:2:0 mode but YCbCr 4:2:0 output not possible. Falling back to RGB.\n");