[PATCH v2 4/5] usb: typec: Implement alternate mode priority handling

[Andrei Kuchynski <akuchynski@xxxxxxxxxxxx>]

This patch introduces APIs to manage the priority of USB Type-C alternate
modes. These APIs allow for setting and retrieving a priority number for
each mode. If a new priority value conflicts with an existing mode's
priority, the priorities of the conflicting mode and all subsequent modes
are automatically incremented to ensure uniqueness.

Signed-off-by: Andrei Kuchynski <akuchynski@xxxxxxxxxxxx>
---
 drivers/usb/typec/Makefile         |  2 +-
 drivers/usb/typec/mode_selection.c | 38 ++++++++++++++++++++++++++++++
 drivers/usb/typec/mode_selection.h |  6 +++++
 include/linux/usb/typec_altmode.h  |  1 +
 4 files changed, 46 insertions(+), 1 deletion(-)
 create mode 100644 drivers/usb/typec/mode_selection.c
 create mode 100644 drivers/usb/typec/mode_selection.h

diff --git a/drivers/usb/typec/Makefile b/drivers/usb/typec/Makefile
index 7a368fea61bc..8a6a1c663eb6 100644
--- a/drivers/usb/typec/Makefile
+++ b/drivers/usb/typec/Makefile
@@ -1,6 +1,6 @@
 # SPDX-License-Identifier: GPL-2.0
 obj-$(CONFIG_TYPEC)		+= typec.o
-typec-y				:= class.o mux.o bus.o pd.o retimer.o
+typec-y				:= class.o mux.o bus.o pd.o retimer.o mode_selection.o
 typec-$(CONFIG_ACPI)		+= port-mapper.o
 obj-$(CONFIG_TYPEC)		+= altmodes/
 obj-$(CONFIG_TYPEC_TCPM)	+= tcpm/
diff --git a/drivers/usb/typec/mode_selection.c b/drivers/usb/typec/mode_selection.c
new file mode 100644
index 000000000000..2179bf25f5d4
--- /dev/null
+++ b/drivers/usb/typec/mode_selection.c
@@ -0,0 +1,38 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright 2025 Google LLC.
+ */
+
+#include "mode_selection.h"
+#include "class.h"
+#include "bus.h"
+
+static int increment_duplicated_priority(struct device *dev, void *data)
+{
+	struct typec_altmode **alt_target = (struct typec_altmode **)data;
+
+	if (is_typec_altmode(dev)) {
+		struct typec_altmode *alt = to_typec_altmode(dev);
+
+		if (alt != *alt_target && alt->priority == (*alt_target)->priority) {
+			alt->priority++;
+			*alt_target = alt;
+			return 1;
+		}
+	}
+
+	return 0;
+}
+
+void typec_mode_set_priority(struct typec_altmode *alt,
+		const unsigned int priority)
+{
+	struct typec_port *port = to_typec_port(alt->dev.parent);
+	int res = 1;
+
+	alt->priority = priority;
+
+	while (res)
+		res = device_for_each_child(&port->dev, &alt,
+				increment_duplicated_priority);
+}
diff --git a/drivers/usb/typec/mode_selection.h b/drivers/usb/typec/mode_selection.h
new file mode 100644
index 000000000000..cbf5a37e6404
--- /dev/null
+++ b/drivers/usb/typec/mode_selection.h
@@ -0,0 +1,6 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#include <linux/usb/typec_altmode.h>
+
+void typec_mode_set_priority(struct typec_altmode *alt,
+		const unsigned int priority);
diff --git a/include/linux/usb/typec_altmode.h b/include/linux/usb/typec_altmode.h
index b3c0866ea70f..571c6e00b54f 100644
--- a/include/linux/usb/typec_altmode.h
+++ b/include/linux/usb/typec_altmode.h
@@ -28,6 +28,7 @@ struct typec_altmode {
 	int				mode;
 	u32				vdo;
 	unsigned int			active:1;
+	unsigned int			priority;
 
 	char				*desc;
 	const struct typec_altmode_ops	*ops;
-- 
2.51.0.rc2.233.g662b1ed5c5-goog