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/class.h | 1 +
drivers/usb/typec/mode_selection.c | 127 +++++++++++++++++++++++++++++
drivers/usb/typec/mode_selection.h | 8 ++
include/linux/usb/typec_altmode.h | 9 ++
5 files changed, 146 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/class.h b/drivers/usb/typec/class.h
index f05d9201c233..c6467e576569 100644
--- a/drivers/usb/typec/class.h
+++ b/drivers/usb/typec/class.h
@@ -82,6 +82,7 @@ struct typec_port {
struct device *usb3_dev;
bool alt_mode_override;
+ struct list_head mode_list;
};
#define to_typec_port(_dev_) container_of(_dev_, struct typec_port, dev)
diff --git a/drivers/usb/typec/mode_selection.c b/drivers/usb/typec/mode_selection.c
new file mode 100644
index 000000000000..8a54639b86bf
--- /dev/null
+++ b/drivers/usb/typec/mode_selection.c
@@ -0,0 +1,127 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright 2025 Google LLC.
+ */
+
+#include <linux/usb/typec_altmode.h>
+#include <linux/slab.h>
+#include <linux/list.h>
+#include "mode_selection.h"
+#include "class.h"
+
+static const char * const mode_names[TYPEC_ALTMODE_MAX] = {
+ [TYPEC_ALTMODE_DP] = "DisplayPort",
+ [TYPEC_ALTMODE_TBT] = "Thunderbolt3",
+ [TYPEC_ALTMODE_USB4] = "USB4",
+};
+
+static const int default_priorities[TYPEC_ALTMODE_MAX] = {
+ [TYPEC_ALTMODE_DP] = 2,
+ [TYPEC_ALTMODE_TBT] = 1,
+ [TYPEC_ALTMODE_USB4] = 0,
+};
+
+static inline enum typec_mode_type typec_svid_to_altmode(const u16 svid)
+{
+ switch (svid) {
+ case USB_TYPEC_DP_SID:
+ return TYPEC_ALTMODE_DP;
+ case USB_TYPEC_TBT_SID:
+ return TYPEC_ALTMODE_TBT;
+ case USB_TYPEC_USB4_SID:
+ return TYPEC_ALTMODE_USB4;
+ }
+ return TYPEC_ALTMODE_MAX;
+}
+
+/**
+ * struct mode_selection_state - State tracking for a specific Type-C mode
+ * @mode: The type of mode this instance represents
+ * @priority: The mode priority. Lower values indicate a more preferred mode.
+ * @list: List head to link this mode state into a prioritized list.
+ */
+struct mode_selection_state {
+ enum typec_mode_type mode;
+ int priority;
+ struct list_head list;
+};
+
+/* -------------------------------------------------------------------------- */
+/* port 'mode_priorities' attribute */
+
+int typec_mode_set_priority(struct typec_altmode *adev, const int priority)
+{
+ struct typec_port *port = to_typec_port(adev->dev.parent);
+ const enum typec_mode_type mode = typec_svid_to_altmode(adev->svid);
+ struct mode_selection_state *ms_target = NULL;
+ struct mode_selection_state *ms, *tmp;
+
+ if (mode >= TYPEC_ALTMODE_MAX || !mode_names[mode])
+ return -EOPNOTSUPP;
+
+ list_for_each_entry_safe(ms, tmp, &port->mode_list, list) {
+ if (ms->mode == mode) {
+ ms_target = ms;
+ list_del(&ms->list);
+ break;
+ }
+ }
+
+ if (!ms_target) {
+ ms_target = kzalloc(sizeof(struct mode_selection_state), GFP_KERNEL);
+ if (!ms_target)
+ return -ENOMEM;
+ ms_target->mode = mode;
+ INIT_LIST_HEAD(&ms_target->list);
+ }
+
+ if (priority >= 0)
+ ms_target->priority = priority;
+ else
+ ms_target->priority = default_priorities[mode];
+
+ while (ms_target) {
+ struct mode_selection_state *ms_peer = NULL;
+
+ list_for_each_entry(ms, &port->mode_list, list)
+ if (ms->priority >= ms_target->priority) {
+ if (ms->priority == ms_target->priority)
+ ms_peer = ms;
+ break;
+ }
+
+ list_add_tail(&ms_target->list, &ms->list);
+ ms_target = ms_peer;
+ if (ms_target) {
+ ms_target->priority++;
+ list_del(&ms_target->list);
+ }
+ }
+
+ return 0;
+}
+
+int typec_mode_get_priority(struct typec_altmode *adev, int *priority)
+{
+ struct typec_port *port = to_typec_port(adev->dev.parent);
+ const enum typec_mode_type mode = typec_svid_to_altmode(adev->svid);
+ struct mode_selection_state *ms;
+
+ list_for_each_entry(ms, &port->mode_list, list)
+ if (ms->mode == mode) {
+ *priority = ms->priority;
+ return 0;
+ }
+
+ return -EOPNOTSUPP;
+}
+
+void typec_mode_selection_destroy(struct typec_port *port)
+{
+ struct mode_selection_state *ms, *tmp;
+
+ list_for_each_entry_safe(ms, tmp, &port->mode_list, list) {
+ list_del(&ms->list);
+ kfree(ms);
+ }
+}
diff --git a/drivers/usb/typec/mode_selection.h b/drivers/usb/typec/mode_selection.h
new file mode 100644
index 000000000000..69adfcf39d7c
--- /dev/null
+++ b/drivers/usb/typec/mode_selection.h
@@ -0,0 +1,8 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#include <linux/usb/typec_dp.h>
+#include <linux/usb/typec_tbt.h>
+
+int typec_mode_set_priority(struct typec_altmode *adev, const int priority);
+int typec_mode_get_priority(struct typec_altmode *adev, int *priority);
+void typec_mode_selection_destroy(struct typec_port *port);
diff --git a/include/linux/usb/typec_altmode.h b/include/linux/usb/typec_altmode.h
index b3c0866ea70f..318858fc7bec 100644
--- a/include/linux/usb/typec_altmode.h
+++ b/include/linux/usb/typec_altmode.h
@@ -145,6 +145,15 @@ enum {
#define TYPEC_MODAL_STATE(_state_) ((_state_) + TYPEC_STATE_MODAL)
+#define USB_TYPEC_USB4_SID 0xff00
+
+enum typec_mode_type {
+ TYPEC_ALTMODE_DP = 0,
+ TYPEC_ALTMODE_TBT,
+ TYPEC_ALTMODE_USB4,
+ TYPEC_ALTMODE_MAX,
+};
+
struct typec_altmode *typec_altmode_get_plug(struct typec_altmode *altmode,
enum typec_plug_index index);
void typec_altmode_put_plug(struct typec_altmode *plug);
--
2.51.0.rc0.215.g125493bb4a-goog
