[PATCH v6 13/22] drm/bridge: dw-hdmi-qp: Add HDMI 2.0 SCDC scrambling support`

[Cristian Ciocaltea <cristian.ciocaltea@collabora.com>]

Enable HDMI 2.0 display modes (e.g. 4K@60Hz) by implementing SCDC
scrambling and high TMDS clock ratio management for TMDS character
rates exceeding the 340 MHz HDMI 1.4b limit.

Reject modes requiring TMDS rates above 600 MHz since those require
HDMI 2.1 FRL which is not yet supported.  In no_hpd configurations,
further restrict to 340 MHz because SCDC requires a connected sink.

Tested-by: Diederik de Haas <diederik@cknow-tech.com>
Tested-by: Maud Spierings <maud_spierings@hotmail.com>
Acked-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@collabora.com>
---
 drivers/gpu/drm/bridge/synopsys/dw-hdmi-qp.c | 76 ++++++++++++++++++++--------
 1 file changed, 56 insertions(+), 20 deletions(-)

diff --git a/drivers/gpu/drm/bridge/synopsys/dw-hdmi-qp.c b/drivers/gpu/drm/bridge/synopsys/dw-hdmi-qp.c
index efa798aa23ac..001916a98da8 100644
--- a/drivers/gpu/drm/bridge/synopsys/dw-hdmi-qp.c
+++ b/drivers/gpu/drm/bridge/synopsys/dw-hdmi-qp.c
@@ -2,6 +2,7 @@
 /*
  * Copyright (c) 2021-2022 Rockchip Electronics Co., Ltd.
  * Copyright (c) 2024 Collabora Ltd.
+ * Copyright (c) 2025 Amazon.com, Inc. or its affiliates.
  *
  * Author: Algea Cao <algea.cao@rock-chips.com>
  * Author: Cristian Ciocaltea <cristian.ciocaltea@collabora.com>
@@ -15,12 +16,12 @@
 #include <linux/module.h>
 #include <linux/mutex.h>
 #include <linux/of.h>
-#include <linux/workqueue.h>
 
 #include <drm/bridge/dw_hdmi_qp.h>
 #include <drm/display/drm_hdmi_helper.h>
 #include <drm/display/drm_hdmi_cec_helper.h>
 #include <drm/display/drm_hdmi_state_helper.h>
+#include <drm/display/drm_scdc_helper.h>
 #include <drm/drm_atomic.h>
 #include <drm/drm_atomic_helper.h>
 #include <drm/drm_bridge.h>
@@ -39,8 +40,7 @@
 #define DDC_SEGMENT_ADDR	0x30
 
 #define HDMI14_MAX_TMDSCLK	340000000
-
-#define SCRAMB_POLL_DELAY_MS	3000
+#define HDMI20_MAX_TMDSRATE	600000000
 
 /*
  * Unless otherwise noted, entries in this table are 100% optimization.
@@ -164,6 +164,7 @@ struct dw_hdmi_qp {
 	} phy;
 
 	unsigned long ref_clk_rate;
+	struct drm_connector *curr_conn;
 	struct regmap *regm;
 	int main_irq;
 
@@ -754,26 +755,35 @@ static void dw_hdmi_qp_bridge_atomic_enable(struct drm_bridge *bridge,
 {
 	struct dw_hdmi_qp *hdmi = bridge->driver_private;
 	struct drm_connector_state *conn_state;
-	struct drm_connector *connector;
 	unsigned int op_mode;
+	int ret;
 
-	connector = drm_atomic_get_new_connector_for_encoder(state, bridge->encoder);
-	if (WARN_ON(!connector))
+	hdmi->curr_conn = drm_atomic_get_new_connector_for_encoder(state,
+								   bridge->encoder);
+	if (WARN_ON(!hdmi->curr_conn))
 		return;
 
-	conn_state = drm_atomic_get_new_connector_state(state, connector);
+	conn_state = drm_atomic_get_new_connector_state(state, hdmi->curr_conn);
 	if (WARN_ON(!conn_state))
 		return;
 
-	if (connector->display_info.is_hdmi) {
-		dev_dbg(hdmi->dev, "%s mode=HDMI %s rate=%llu bpc=%u\n", __func__,
-			drm_hdmi_connector_get_output_format_name(conn_state->hdmi.output_format),
-			conn_state->hdmi.tmds_char_rate, conn_state->hdmi.output_bpc);
+	if (hdmi->curr_conn->display_info.is_hdmi) {
 		op_mode = 0;
 		hdmi->tmds_char_rate = conn_state->hdmi.tmds_char_rate;
+
+		if (hdmi->tmds_char_rate > HDMI14_MAX_TMDSCLK) {
+			ret = drm_scdc_start_scrambling(hdmi->curr_conn);
+			if (ret)
+				dev_warn(hdmi->dev, "Failed to setup SCDC: %d\n", ret);
+		}
+
+		dev_dbg(hdmi->dev, "%s mode=HDMI %s rate=%llu bpc=%u scramb=%d\n", __func__,
+			drm_hdmi_connector_get_output_format_name(conn_state->hdmi.output_format),
+			conn_state->hdmi.tmds_char_rate, conn_state->hdmi.output_bpc,
+			hdmi->curr_conn->hdmi.scrambler_enabled);
 	} else {
-		dev_dbg(hdmi->dev, "%s mode=DVI\n", __func__);
 		op_mode = OPMODE_DVI;
+		dev_dbg(hdmi->dev, "%s mode=DVI\n", __func__);
 	}
 
 	hdmi->phy.ops->init(hdmi, hdmi->phy.data);
@@ -781,7 +791,7 @@ static void dw_hdmi_qp_bridge_atomic_enable(struct drm_bridge *bridge,
 	dw_hdmi_qp_mod(hdmi, HDCP2_BYPASS, HDCP2_BYPASS, HDCP2LOGIC_CONFIG0);
 	dw_hdmi_qp_mod(hdmi, op_mode, OPMODE_DVI, LINK_CONFIG0);
 
-	drm_atomic_helper_connector_hdmi_update_infoframes(connector, state);
+	drm_atomic_helper_connector_hdmi_update_infoframes(hdmi->curr_conn, state);
 }
 
 static void dw_hdmi_qp_bridge_atomic_disable(struct drm_bridge *bridge,
@@ -791,6 +801,9 @@ static void dw_hdmi_qp_bridge_atomic_disable(struct drm_bridge *bridge,
 
 	hdmi->tmds_char_rate = 0;
 
+	drm_scdc_stop_scrambling(hdmi->curr_conn);
+
+	hdmi->curr_conn = NULL;
 	hdmi->phy.ops->disable(hdmi, hdmi->phy.data);
 }
 
@@ -832,12 +845,12 @@ dw_hdmi_qp_bridge_tmds_char_rate_valid(const struct drm_bridge *bridge,
 {
 	struct dw_hdmi_qp *hdmi = bridge->driver_private;
 
-	/*
-	 * TODO: when hdmi->no_hpd is 1 we must not support modes that
-	 * require scrambling, including every mode with a clock above
-	 * HDMI14_MAX_TMDSCLK.
-	 */
-	if (rate > HDMI14_MAX_TMDSCLK) {
+	if (hdmi->no_hpd && rate > HDMI14_MAX_TMDSCLK) {
+		dev_dbg(hdmi->dev, "Unsupported TMDS char rate in no_hpd mode: %lld\n", rate);
+		return MODE_CLOCK_HIGH;
+	}
+
+	if (rate > HDMI20_MAX_TMDSRATE) {
 		dev_dbg(hdmi->dev, "Unsupported TMDS char rate: %lld\n", rate);
 		return MODE_CLOCK_HIGH;
 	}
@@ -845,6 +858,26 @@ dw_hdmi_qp_bridge_tmds_char_rate_valid(const struct drm_bridge *bridge,
 	return MODE_OK;
 }
 
+static int dw_hdmi_qp_bridge_scrambler_enable(struct drm_bridge *bridge)
+{
+	struct dw_hdmi_qp *hdmi = bridge->driver_private;
+
+	dw_hdmi_qp_write(hdmi, 1, SCRAMB_CONFIG0);
+	dev_dbg(hdmi->dev, "scrambler enabled\n");
+
+	return 0;
+}
+
+static int dw_hdmi_qp_bridge_scrambler_disable(struct drm_bridge *bridge)
+{
+	struct dw_hdmi_qp *hdmi = bridge->driver_private;
+
+	dw_hdmi_qp_write(hdmi, 0, SCRAMB_CONFIG0);
+	dev_dbg(hdmi->dev, "scrambler disabled\n");
+
+	return 0;
+}
+
 static int dw_hdmi_qp_bridge_clear_avi_infoframe(struct drm_bridge *bridge)
 {
 	struct dw_hdmi_qp *hdmi = bridge->driver_private;
@@ -1218,6 +1251,8 @@ static const struct drm_bridge_funcs dw_hdmi_qp_bridge_funcs = {
 	.hpd_disable = dw_hdmi_qp_bridge_hpd_disable,
 	.edid_read = dw_hdmi_qp_bridge_edid_read,
 	.hdmi_tmds_char_rate_valid = dw_hdmi_qp_bridge_tmds_char_rate_valid,
+	.hdmi_scrambler_enable = dw_hdmi_qp_bridge_scrambler_enable,
+	.hdmi_scrambler_disable = dw_hdmi_qp_bridge_scrambler_disable,
 	.hdmi_clear_avi_infoframe = dw_hdmi_qp_bridge_clear_avi_infoframe,
 	.hdmi_write_avi_infoframe = dw_hdmi_qp_bridge_write_avi_infoframe,
 	.hdmi_clear_hdmi_infoframe = dw_hdmi_qp_bridge_clear_hdmi_infoframe,
@@ -1344,7 +1379,8 @@ struct dw_hdmi_qp *dw_hdmi_qp_bind(struct platform_device *pdev,
 			   DRM_BRIDGE_OP_HDMI |
 			   DRM_BRIDGE_OP_HDMI_AUDIO |
 			   DRM_BRIDGE_OP_HDMI_HDR_DRM_INFOFRAME |
-			   DRM_BRIDGE_OP_HDMI_SPD_INFOFRAME;
+			   DRM_BRIDGE_OP_HDMI_SPD_INFOFRAME |
+			   DRM_BRIDGE_OP_HDMI_SCRAMBLER;
 	if (!hdmi->no_hpd)
 		hdmi->bridge.ops |= DRM_BRIDGE_OP_HPD;
 	hdmi->bridge.of_node = pdev->dev.of_node;

-- 
2.53.0