drm/i915/hdmi: 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/20260409101539.22032-9-ville.syrjala@linux.intel.com
Tested-by: Nicolas Frattaroli <nicolas.frattaroli@collabora.com>

diff --git a/drivers/gpu/drm/i915/display/intel_hdmi.c b/drivers/gpu/drm/i915/display/intel_hdmi.c
index 79093d8fc2e61daff29de6bfa573782846155bc4..874076a29da4e7a2f1b97684f3872440a03e50a2 100644 (file)
--- a/drivers/gpu/drm/i915/display/intel_hdmi.c
+++ b/drivers/gpu/drm/i915/display/intel_hdmi.c
@@ -2314,7 +2314,7 @@ static int intel_hdmi_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");