[PATCH] drm/i915/hdmi: Prune unsupported modes as per HDMI2.1 spec

[Ankit Nautiyal]

As per Sec 7.8.1 of HDMI2.1 spec, source tha support modes:
4K100, 4K120, 8K50, 8K60 must support these modes in atleast one of
the below formats:
i) uncompressed FRL, 420 format and min of 10 bpc, or
ii) compressed FRL, 444 format and min of 10 bpc.

Since FRL and DSC are not supported natively with HDMI, the above
modes must be pruned as per the spec, and is a requirement for the
HDMI2.1 compliance test.

This patch adds a condition to check for the modes with clock
requirement more than 2376 MHz (1188 MHz with 420 format),
and prune them if none of the above two formats are supported.

Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal at intel.com>
---
 drivers/gpu/drm/i915/display/intel_hdmi.c | 42 +++++++++++++++++++++++
 1 file changed, 42 insertions(+)

diff --git a/drivers/gpu/drm/i915/display/intel_hdmi.c b/drivers/gpu/drm/i915/display/intel_hdmi.c
index a4a6f8bd2841..ee3e98e515d7 100644
--- a/drivers/gpu/drm/i915/display/intel_hdmi.c
+++ b/drivers/gpu/drm/i915/display/intel_hdmi.c
@@ -1939,6 +1939,37 @@ static bool intel_hdmi_sink_bpc_possible(struct drm_connector *connector,
 	}
 }
 
+/*
+ * HDMI2.1 Sec7.8.1
+ * Support requirement for 4K100, 4K120, 8K50, and 8K60.
+ *
+ * The modes with timings same as above modes are supported only with min of 10 bpc
+ * along with:
+ *
+ * i) 444 format only with FRL mode support with DSC
+ * ii) 420 format only with FRL mode without DSC.
+ */
+static bool
+intel_hdmi21_bpc_possible(int clock, int bpc, bool ycbcr420_output,
+			  bool frl_supported, bool dsc_supported)
+{
+	int pixel_clock = ycbcr420_output ? clock * 2 : clock;
+
+	if (pixel_clock < 2376000)
+		return true;
+
+	if (!frl_supported)
+		return false;
+
+	if (!ycbcr420_output && !dsc_supported)
+		return false;
+
+	if (bpc < 10)
+		return false;
+
+	return true;
+}
+
 static enum drm_mode_status
 intel_hdmi_mode_clock_valid(struct drm_connector *connector, int clock,
 			    bool has_hdmi_sink, bool ycbcr420_output)
@@ -1947,6 +1978,14 @@ intel_hdmi_mode_clock_valid(struct drm_connector *connector, int clock,
 	struct intel_hdmi *hdmi = intel_attached_hdmi(to_intel_connector(connector));
 	enum drm_mode_status status = MODE_OK;
 	int bpc;
+	bool frl, dsc;
+
+	/*
+	 * FRL and DSC not supported for HDMI not supported from source
+	 * as of now.
+	 */
+	frl = false;
+	dsc = false;
 
 	/*
 	 * Try all color depths since valid port clock range
@@ -1962,6 +2001,9 @@ intel_hdmi_mode_clock_valid(struct drm_connector *connector, int clock,
 		if (!intel_hdmi_sink_bpc_possible(connector, bpc, has_hdmi_sink, ycbcr420_output))
 			continue;
 
+		if (!intel_hdmi21_bpc_possible(clock, bpc, ycbcr420_output, frl, dsc))
+			continue;
+
 		status = hdmi_port_clock_valid(hdmi, tmds_clock, true, has_hdmi_sink);
 		if (status == MODE_OK)
 			return MODE_OK;
-- 
2.25.1