phy: qcom-qmp-combo: Introduce drm_bridge

The QMP combo PHY sits in an of_graph connected between the DisplayPort
controller and a USB Type-C connector (or possibly a redriver).

The TCPM needs to be able to convey the HPD signal to the DisplayPort
controller, but no directly link is provided by DeviceTree so the signal
needs to "pass through" the QMP combo phy.

Handle this by introducing a drm_bridge which upon initialization finds
the next bridge (i.e. the usb-c-connector) and chain this together. This
way HPD changes in the connector will propagate to the DisplayPort
driver.

The connector bridge is resolved lazily, as the TCPM is expected to be
able to resolve the typec mux and switch at probe time, so the QMP combo
phy will probe before the TCPM.

Acked-by: Neil Armstrong <[e-mail]>
Tested-by: Bryan O'Donoghue <[e-mail]>
Reviewed-by: Bryan O'Donoghue <[e-mail]>
Tested-by: Abel Vesa <[e-mail]>
Tested-by: Steev Klimaszewski <[e-mail]>
Tested-by: Neil Armstrong <[e-mail]> # on HDK8450
Tested-by: Johan Hovold <[e-mail]> # X13s
Reviewed-by: Johan Hovold <[e-mail]>
Signed-off-by: Bjorn Andersson <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Vinod Koul <[e-mail]>

drivers/phy/qualcomm/Kconfig

···
 	tristate "Qualcomm QMP Combo PHY Driver"
 	default PHY_QCOM_QMP
 	depends on TYPEC || TYPEC=n
+	depends on DRM || DRM=n
 	select GENERIC_PHY
 	select MFD_SYSCON
+	select DRM_PANEL_BRIDGE if DRM
 	help
 	  Enable this to support the QMP Combo PHY transceiver that is used
 	  with USB3 and DisplayPort controllers on Qualcomm chips.

drivers/phy/qualcomm/phy-qcom-qmp-combo.c

···
 #include <linux/usb/typec.h>
 #include <linux/usb/typec_mux.h>
 
+#include <drm/drm_bridge.h>
+
 #include <dt-bindings/phy/phy-qcom-qmp.h>
 
 #include "phy-qcom-qmp.h"
···
 	struct clk_fixed_rate pipe_clk_fixed;
 	struct clk_hw dp_link_hw;
 	struct clk_hw dp_pixel_hw;
+
+	struct drm_bridge bridge;
 
 	struct typec_switch_dev *sw;
 	enum typec_orientation orientation;
···
 }
 #endif
 
+#if IS_ENABLED(CONFIG_DRM)
+static int qmp_combo_bridge_attach(struct drm_bridge *bridge,
+				   enum drm_bridge_attach_flags flags)
+{
+	struct qmp_combo *qmp = container_of(bridge, struct qmp_combo, bridge);
+	struct drm_bridge *next_bridge;
+
+	if (!(flags & DRM_BRIDGE_ATTACH_NO_CONNECTOR))
+		return -EINVAL;
+
+	next_bridge = devm_drm_of_get_bridge(qmp->dev, qmp->dev->of_node, 0, 0);
+	if (IS_ERR(next_bridge)) {
+		dev_err(qmp->dev, "failed to acquire drm_bridge: %pe\n", next_bridge);
+		return PTR_ERR(next_bridge);
+	}
+
+	return drm_bridge_attach(bridge->encoder, next_bridge, bridge,
+				 DRM_BRIDGE_ATTACH_NO_CONNECTOR);
+}
+
+static const struct drm_bridge_funcs qmp_combo_bridge_funcs = {
+	.attach	= qmp_combo_bridge_attach,
+};
+
+static int qmp_combo_dp_register_bridge(struct qmp_combo *qmp)
+{
+	qmp->bridge.funcs = &qmp_combo_bridge_funcs;
+	qmp->bridge.of_node = qmp->dev->of_node;
+
+	return devm_drm_bridge_add(qmp->dev, &qmp->bridge);
+}
+#else
+static int qmp_combo_dp_register_bridge(struct qmp_combo *qmp)
+{
+	return 0;
+}
+#endif
+
 static int qmp_combo_parse_dt_lecacy_dp(struct qmp_combo *qmp, struct device_node *np)
 {
 	struct device *dev = qmp->dev;
···
 		return ret;
 
 	ret = qmp_combo_typec_switch_register(qmp);
+	if (ret)
+		return ret;
+
+	ret = qmp_combo_dp_register_bridge(qmp);
 	if (ret)
 		return ret;