drm/display: hdmi: Add HDMI 2.0 scrambling management helpers

Add helpers to manage the full lifecycle of HDMI 2.0 SCDC scrambling on both source and sink sides: - drm_hdmi_mode_needs_scrambling(): checks whether a mode, bits per component and output format combination requires scrambling, which is needed when the resulting TMDS character rate exceeds the HDMI 1.3 maximum of 340 MHz - drm_connector_hdmi_enable_scrambling(): configures SCDC scrambling and high TMDS clock ratio and starts a periodic work item that monitors the sink's SCDC scrambling status, retrying setup when the sink loses state - drm_connector_hdmi_disable_scrambling(): tears down scrambling on both sides and cancels the monitoring work - drm_connector_hdmi_sync_scdc(): triggers a CRTC reset on reconnection to restore SCDC state lost during sink disconnects within an active display pipeline Tested-by: Maud Spierings <maud_spierings@hotmail.com> Tested-by: Diederik de Haas <diederik@cknow-tech.com> # NanoPC-T6 LTS, Rock 5B Reviewed-by: Maxime Ripard <mripard@kernel.org> Tested-by: Igor Paunovic <royalnet026@gmail.com> # RK3588 Orange Pi 5 Plus, dual HDMI Tested-by: Robin Räber <robin.raebi@gmail.com> Link: https://patch.msgid.link/20260901-dw-hdmi-qp-scramb-v11-10-bc12954a0688@collabora.com Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@collabora.com>
2026-11-07 06:17:02 +01:00 · 2026-09-01 21:50:34 +03:00 · 2026-09-01 21:50:34 +03:00 · d653818324
commit d653818324
parent f57c219838
2 changed files with 312 additions and 0 deletions
--- a/drivers/gpu/drm/display/drm_hdmi_helper.c
+++ b/drivers/gpu/drm/display/drm_hdmi_helper.c
@ -4,12 +4,20 @@
 #include <linux/module.h>

 #include <drm/display/drm_hdmi_helper.h>
+#include <drm/display/drm_scdc_helper.h>
+
+#include <drm/drm_atomic.h>
+#include <drm/drm_atomic_helper.h>
 #include <drm/drm_connector.h>
+#include <drm/drm_crtc.h>
 #include <drm/drm_edid.h>
 #include <drm/drm_modes.h>
+#include <drm/drm_modeset_lock.h>
 #include <drm/drm_print.h>
 #include <drm/drm_property.h>

+#define DRM_HDMI_SCDC_POLL_DELAY_MS	1000
+
 static inline bool is_eotf_supported(u8 output_eotf, u8 sink_eotf)
 {
 	return sink_eotf & BIT(output_eotf);
@ -426,3 +434,292 @@ drm_hdmi_acr_get_n_cts(unsigned long long tmds_char_rate,
 	*out_cts = cts;
 }
 EXPORT_SYMBOL(drm_hdmi_acr_get_n_cts);
+
+/**
+ * drm_hdmi_mode_needs_scrambling() - Check if an HDMI mode requires scrambling
+ * @mode: Display mode to check
+ * @bpc: Bits per color component
+ * @fmt: Output pixel format
+ *
+ * Computes the TMDS character rate for the given mode, bits per component and
+ * output format, and checks whether it exceeds the HDMI 1.3 maximum TMDS
+ * character rate of 340 MHz.
+ *
+ * Returns:
+ * true if the mode requires scrambling, false otherwise.
+ */
+bool drm_hdmi_mode_needs_scrambling(const struct drm_display_mode *mode,
+				    unsigned int bpc,
+				    enum drm_output_color_format fmt)
+{
+	unsigned long long tmds_char_rate;
+
+	tmds_char_rate = drm_hdmi_compute_mode_clock(mode, bpc, fmt);
+
+	return tmds_char_rate > HDMI_1_3_TMDS_CHAR_RATE_MAX_HZ;
+}
+EXPORT_SYMBOL(drm_hdmi_mode_needs_scrambling);
+
+static bool drm_scdc_sink_supports_scrambling(struct drm_connector *connector)
+{
+	const struct drm_display_info *info = &connector->display_info;
+
+	return info->is_hdmi &&
+	       info->hdmi.scdc.supported &&
+	       info->hdmi.scdc.scrambling.supported;
+}
+
+static int drm_connector_hdmi_try_scrambling_setup(struct drm_connector *connector)
+{
+	bool done;
+
+	done = drm_scdc_set_high_tmds_clock_ratio(connector, true);
+	if (!done)
+		return -EIO;
+
+	done = drm_scdc_set_scrambling(connector, true);
+	if (!done)
+		return -EIO;
+
+	if (READ_ONCE(connector->hdmi.scrambler_enabled))
+		schedule_delayed_work(&connector->hdmi.scdc_work,
+				      msecs_to_jiffies(DRM_HDMI_SCDC_POLL_DELAY_MS));
+
+	return 0;
+}
+
+static void drm_connector_hdmi_scdc_work(struct work_struct *work)
+{
+	struct drm_connector *connector;
+	struct drm_connector_hdmi *hdmi;
+
+	hdmi = container_of(to_delayed_work(work), struct drm_connector_hdmi,
+			    scdc_work);
+	connector = container_of(hdmi, struct drm_connector, hdmi);
+
+	/*
+	 * The connector, and hence this work item, may outlive the source
+	 * driver, e.g. when userspace keeps a DRM file descriptor open past
+	 * unbind. Never poke the DDC bus after the connector got unregistered,
+	 * as the underlying I2C adapter may already be gone.
+	 */
+	if (drm_connector_is_unregistered(connector))
+		return;
+
+	if (READ_ONCE(connector->hdmi.scrambler_enabled) &&
+	    !drm_scdc_get_scrambling_status(connector))
+		drm_connector_hdmi_try_scrambling_setup(connector);
+}
+
+/**
+ * drm_connector_hdmi_enable_scrambling() - enable scrambling and monitor SCDC status
+ * @connector: connector
+ * @conn_state: connector state
+ *
+ * Enables scrambling and high TMDS clock ratio on both source and sink sides.
+ * Additionally, use a delayed work item to monitor the scrambling status on
+ * the sink side and retry the operation, as some displays refuse to set the
+ * scrambling bit right away.
+ *
+ * The work item is cancelled by drm_connector_hdmi_disable_scrambling(), hence
+ * source drivers must ensure the display pipeline is shut down on unbind, e.g.
+ * via drm_atomic_helper_shutdown(). Otherwise the work may outlive the driver's
+ * devres-managed resources, since the connector itself is only cleaned up when
+ * the last reference to the DRM device is dropped.
+ *
+ * Returns:
+ * Zero if scrambling is set successfully, an error code otherwise.
+ */
+int drm_connector_hdmi_enable_scrambling(struct drm_connector *connector,
+					 const struct drm_connector_state *conn_state)
+{
+	struct drm_connector_hdmi *hdmi = &connector->hdmi;
+	struct drm_device *dev = connector->dev;
+	int ret;
+
+	if (!conn_state)
+		return -EINVAL;
+
+	if (!conn_state->hdmi.scrambler_needed)
+		return 0;
+
+	if (!drm_connector_hdmi_scrambler_supported(connector)) {
+		drm_dbg_kms(dev, "Source doesn't support scrambling.\n");
+		return -EINVAL;
+	}
+
+	if (!drm_scdc_sink_supports_scrambling(connector)) {
+		drm_dbg_kms(dev, "Sink doesn't support scrambling.\n");
+		return -EINVAL;
+	}
+
+	if (!connector->ddc)
+		return -EINVAL;
+
+	drm_dbg_kms(dev, "Enabling scrambling\n");
+
+	if (!hdmi->scdc_work_initialized) {
+		INIT_DELAYED_WORK(&hdmi->scdc_work,
+				  drm_connector_hdmi_scdc_work);
+		hdmi->scdc_work_initialized = true;
+	}
+
+	WRITE_ONCE(hdmi->scrambler_enabled, true);
+
+	ret = drm_connector_hdmi_try_scrambling_setup(connector);
+	if (!ret)
+		ret = hdmi->funcs->scrambler_enable(connector);
+
+	if (ret) {
+		WRITE_ONCE(hdmi->scrambler_enabled, false);
+		cancel_delayed_work_sync(&hdmi->scdc_work);
+
+		drm_scdc_set_scrambling(connector, false);
+		drm_scdc_set_high_tmds_clock_ratio(connector, false);
+	}
+
+	return ret;
+}
+EXPORT_SYMBOL(drm_connector_hdmi_enable_scrambling);
+
+/**
+ * drm_connector_hdmi_disable_scrambling() - disable scrambling and SCDC monitoring
+ * @connector: connector
+ *
+ * Disables scrambling and high TMDS clock ratio on both source and sink sides.
+ * Also cancels the SCDC status monitoring work item, if it is still pending.
+ *
+ * Returns:
+ * Zero if scrambling is reset successfully, an error code otherwise.
+ */
+int drm_connector_hdmi_disable_scrambling(struct drm_connector *connector)
+{
+	struct drm_connector_hdmi *hdmi = &connector->hdmi;
+	struct drm_device *dev = connector->dev;
+
+	if (!READ_ONCE(hdmi->scrambler_enabled))
+		return 0;
+
+	drm_dbg_kms(dev, "Disabling scrambling\n");
+
+	WRITE_ONCE(hdmi->scrambler_enabled, false);
+
+	/*
+	 * A driver may force scrambler_enabled at init to trigger a disable
+	 * at boot (e.g. vc4), bypassing the enable path that sets up the work
+	 * item. Only cancel it once it has actually been initialized.
+	 */
+	if (hdmi->scdc_work_initialized)
+		cancel_delayed_work_sync(&hdmi->scdc_work);
+
+	if (connector->ddc &&
+	    connector->status == connector_status_connected &&
+	    drm_scdc_sink_supports_scrambling(connector)) {
+		drm_scdc_set_scrambling(connector, false);
+		drm_scdc_set_high_tmds_clock_ratio(connector, false);
+	}
+
+	return hdmi->funcs->scrambler_disable(connector);
+}
+EXPORT_SYMBOL(drm_connector_hdmi_disable_scrambling);
+
+/**
+ * drm_connector_hdmi_sync_scdc() - resync the sink-side SCDC upon reconnect
+ * @connector: connector
+ * @plugged: connector plugged status event
+ * @ctx: initialized lock acquisition context
+ *
+ * When receiving hotplug disconnect/reconnect event, while the display is
+ * still active (CRTC enabled), the SCDC status on the sink side is reset
+ * and must be explicitly restored.
+ *
+ * The typical solution for this is to trigger an empty modeset in
+ * drm_connector_helper_funcs.detect_ctx(), which is what this helper does
+ * by triggering a CRTC reset on reconnection.
+ *
+ * When making use of the HDMI connector framework, this is automatically
+ * triggered via drm_atomic_helper_connector_hdmi_hotplug().
+ *
+ * Returns:
+ * Zero on success, an error code otherwise, including -EDEADLK.
+ */
+int drm_connector_hdmi_sync_scdc(struct drm_connector *connector, bool plugged,
+				 struct drm_modeset_acquire_ctx *ctx)
+{
+	struct drm_connector_hdmi *hdmi = &connector->hdmi;
+	struct drm_device *dev = connector->dev;
+	struct drm_connector_state *conn_state;
+	struct drm_crtc *crtc;
+	u8 config;
+	int ret;
+
+	if (!connector || !plugged || !ctx)
+		return 0;
+
+	/*
+	 * This is normally part of .detect_ctx() call path, which already holds
+	 * connection_mutex through @ctx.  However, re-acquiring it with the
+	 * same context is a no-op and makes the helper safe under any caller.
+	 */
+	ret = drm_modeset_lock(&connector->dev->mode_config.connection_mutex, ctx);
+	if (ret)
+		return ret;
+
+	/* TODO: Also handle HDMI 2.1 FRL link training */
+
+	if (!drm_connector_hdmi_scrambler_supported(connector) ||
+	    !READ_ONCE(hdmi->scrambler_enabled))
+		return 0;
+
+	conn_state = connector->state;
+	if (!conn_state)
+		return 0;
+
+	crtc = conn_state->crtc;
+	if (!crtc)
+		return 0;
+
+	ret = drm_modeset_lock(&crtc->mutex, ctx);
+	if (ret)
+		return ret;
+
+	if (!crtc->state || !crtc->state->active)
+		return 0;
+
+	if (!connector->ddc || !drm_scdc_sink_supports_scrambling(connector))
+		return 0;
+
+	if (conn_state->commit &&
+	    !try_wait_for_completion(&conn_state->commit->hw_done))
+		return 0;
+
+	ret = drm_scdc_readb(connector->ddc, SCDC_TMDS_CONFIG, &config);
+	if (ret) {
+		drm_dbg_kms(dev, "Failed to read TMDS config: %d\n", ret);
+		return ret;
+	}
+
+	if (config & SCDC_SCRAMBLING_ENABLE)
+		return 0;
+
+	/*
+	 * HDMI 2.0 requires that one should not send scrambled data prior
+	 * to configuring the sink scrambling, and that TMDS clock/data
+	 * transmission should be suspended when changing the TMDS clock rate
+	 * in the sink.  So let's just do a full modeset here, even though some
+	 * sinks would be perfectly happy if were to just reconfigure the SCDC
+	 * settings on the fly.
+	 *
+	 * The disable/re-enable cycle triggered by the reset should call
+	 * drm_connector_hdmi_enable_scrambling() during re-enable, thus
+	 * properly configuring the sink before data transmission resumes.
+	 */
+	drm_dbg_kms(dev, "Resetting CRTC to restore SCDC status\n");
+
+	ret = drm_atomic_helper_reset_crtc(crtc, ctx);
+	if (ret && ret != -EDEADLK)
+		drm_dbg_kms(dev, "Failed to reset CRTC: %d\n", ret);
+
+	return ret;
+}
+EXPORT_SYMBOL(drm_connector_hdmi_sync_scdc);
--- a/include/drm/display/drm_hdmi_helper.h
+++ b/include/drm/display/drm_hdmi_helper.h
@ -8,6 +8,7 @@
 struct drm_connector;
 struct drm_connector_state;
 struct drm_display_mode;
+struct drm_modeset_acquire_ctx;
 enum drm_output_color_format;

 void
@ -35,4 +36,18 @@ drm_hdmi_acr_get_n_cts(unsigned long long tmds_char_rate,
 		       unsigned int *out_n,
 		       unsigned int *out_cts);

+bool
+drm_hdmi_mode_needs_scrambling(const struct drm_display_mode *mode,
+			       unsigned int bpc, enum drm_output_color_format fmt);
+
+int
+drm_connector_hdmi_enable_scrambling(struct drm_connector *connector,
+				     const struct drm_connector_state *conn_state);
+int
+drm_connector_hdmi_disable_scrambling(struct drm_connector *connector);
+
+int
+drm_connector_hdmi_sync_scdc(struct drm_connector *connector, bool plugged,
+			     struct drm_modeset_acquire_ctx *ctx);
+
 #endif