drm/connector: hdmi: Calculate TMDS character rate

Most HDMI drivers have some code to calculate the TMDS character rate,
usually to adjust an internal clock to match what the mode requires.

Since the TMDS character rates mostly depends on the resolution, whether
we need to repeat pixels or not, the bpc count and the format, we can
now derive it from the HDMI connector state that stores all those infos
and remove the duplication from drivers.

Reviewed-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240527-kms-hdmi-connector-state-v15-11-c5af16c3aae2@kernel.org
Signed-off-by: Maxime Ripard <mripard@kernel.org>

drivers/gpu/drm/display/drm_hdmi_state_helper.c

@@ -3,6 +3,7 @@
 #include <drm/drm_atomic.h>
 #include <drm/drm_connector.h>
 
+#include <drm/display/drm_hdmi_helper.h>
 #include <drm/display/drm_hdmi_state_helper.h>
 
 /**
@@ -25,6 +26,63 @@ void __drm_atomic_helper_connector_hdmi_reset(struct drm_connector *connector,
 }
 EXPORT_SYMBOL(__drm_atomic_helper_connector_hdmi_reset);
 
+static const struct drm_display_mode *
+connector_state_get_mode(const struct drm_connector_state *conn_state)
+{
+	struct drm_atomic_state *state;
+	struct drm_crtc_state *crtc_state;
+	struct drm_crtc *crtc;
+
+	state = conn_state->state;
+	if (!state)
+		return NULL;
+
+	crtc = conn_state->crtc;
+	if (!crtc)
+		return NULL;
+
+	crtc_state = drm_atomic_get_new_crtc_state(state, crtc);
+	if (!crtc_state)
+		return NULL;
+
+	return &crtc_state->mode;
+}
+
+static enum drm_mode_status
+hdmi_clock_valid(const struct drm_connector *connector,
+		 const struct drm_display_mode *mode,
+		 unsigned long long clock)
+{
+	const struct drm_display_info *info = &connector->display_info;
+
+	if (info->max_tmds_clock && clock > info->max_tmds_clock * 1000)
+		return MODE_CLOCK_HIGH;
+
+	return MODE_OK;
+}
+
+static int
+hdmi_compute_clock(const struct drm_connector *connector,
+		   struct drm_connector_state *conn_state,
+		   const struct drm_display_mode *mode,
+		   unsigned int bpc, enum hdmi_colorspace fmt)
+{
+	enum drm_mode_status status;
+	unsigned long long clock;
+
+	clock = drm_hdmi_compute_mode_clock(mode, bpc, fmt);
+	if (!clock)
+		return -EINVAL;
+
+	status = hdmi_clock_valid(connector, mode, clock);
+	if (status != MODE_OK)
+		return -EINVAL;
+
+	conn_state->hdmi.tmds_char_rate = clock;
+
+	return 0;
+}
+
 /**
  * drm_atomic_helper_connector_hdmi_check() - Helper to check HDMI connector atomic state
  * @connector: DRM Connector
@@ -44,6 +102,15 @@ int drm_atomic_helper_connector_hdmi_check(struct drm_connector *connector,
 		drm_atomic_get_old_connector_state(state, connector);
 	struct drm_connector_state *new_conn_state =
 		drm_atomic_get_new_connector_state(state, connector);
+	const struct drm_display_mode *mode =
+		connector_state_get_mode(new_conn_state);
+	int ret;
+
+	ret = hdmi_compute_clock(connector, new_conn_state, mode,
+				 new_conn_state->hdmi.output_bpc,
+				 new_conn_state->hdmi.output_format);
+	if (ret)
+		return ret;
 
 	if (old_conn_state->hdmi.output_bpc != new_conn_state->hdmi.output_bpc ||
 	    old_conn_state->hdmi.output_format != new_conn_state->hdmi.output_format) {

drivers/gpu/drm/drm_atomic.c

@@ -1148,6 +1148,7 @@ static void drm_atomic_connector_print_state(struct drm_printer *p,
 		drm_printf(p, "\toutput_bpc=%u\n", state->hdmi.output_bpc);
 		drm_printf(p, "\toutput_format=%s\n",
 			   drm_hdmi_connector_get_output_format_name(state->hdmi.output_format));
+		drm_printf(p, "\ttmds_char_rate=%llu\n", state->hdmi.tmds_char_rate);
 	}
 
 	if (connector->connector_type == DRM_MODE_CONNECTOR_WRITEBACK)

drivers/gpu/drm/tests/drm_hdmi_state_helper_test.c

@@ -72,6 +72,9 @@ static int light_up_connector(struct kunit *test,
 	conn_state = drm_atomic_get_connector_state(state, connector);
 	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, conn_state);
 
+	conn_state->hdmi.output_bpc = connector->max_bpc;
+	conn_state->hdmi.output_format = HDMI_COLORSPACE_RGB;
+
 	ret = drm_atomic_set_crtc_for_connector(conn_state, crtc);
 	KUNIT_EXPECT_EQ(test, ret, 0);
 

include/drm/drm_connector.h

@@ -1049,6 +1049,11 @@ struct drm_connector_state {
 		 * @output_format: Pixel format to output in.
 		 */
 		enum hdmi_colorspace output_format;
+
+		/**
+		 * @tmds_char_rate: TMDS Character Rate, in Hz.
+		 */
+		unsigned long long tmds_char_rate;
 	} hdmi;
 };