Message-ID: <20250630141239.3174390-5-akuchynski@chromium.org>
Date: Mon, 30 Jun 2025 14:12:33 +0000
From: Andrei Kuchynski <akuchynski@...omium.org>
To: Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
	Abhishek Pandit-Subedi <abhishekpandit@...omium.org>,
	Benson Leung <bleung@...omium.org>,
	Jameson Thies <jthies@...gle.com>,
	Tzung-Bi Shih <tzungbi@...nel.org>,
	linux-usb@...r.kernel.org,
	chrome-platform@...ts.linux.dev
Cc: Guenter Roeck <groeck@...omium.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Dmitry Baryshkov <lumag@...nel.org>,
	"Christian A. Ehrhardt" <lk@...e.de>,
	linux-kernel@...r.kernel.org,
	Andrei Kuchynski <akuchynski@...omium.org>
Subject: [PATCH v2 04/10] usb: typec: Expose mode priorities via sysfs

This sysfs attribute specifies the preferred order for enabling
DisplayPort, Thunderbolt alternate modes, and USB4 mode.

Signed-off-by: Andrei Kuchynski <akuchynski@...omium.org>
---
 Documentation/ABI/testing/sysfs-class-typec |  16 +++
 drivers/usb/typec/Makefile                  |   2 +-
 drivers/usb/typec/class.c                   |  28 ++++-
 drivers/usb/typec/class.h                   |   4 +
 drivers/usb/typec/mode_selection.c          | 116 ++++++++++++++++++++
 drivers/usb/typec/mode_selection.h          |  19 ++++
 include/linux/usb/typec_altmode.h           |   7 ++
 7 files changed, 190 insertions(+), 2 deletions(-)
 create mode 100644 drivers/usb/typec/mode_selection.c
 create mode 100644 drivers/usb/typec/mode_selection.h

diff --git a/Documentation/ABI/testing/sysfs-class-typec b/Documentation/ABI/testing/sysfs-class-typec
index 38e101c17a00..ff3296ee8e1c 100644
--- a/Documentation/ABI/testing/sysfs-class-typec
+++ b/Documentation/ABI/testing/sysfs-class-typec
@@ -162,6 +162,22 @@ Description:	Lists the supported USB Modes. The default USB mode that is used
 		- usb3 (USB 3.2)
 		- usb4 (USB4)
 
+What:		/sys/class/typec/<port>/mode_priorities
+Date:		June 2025
+Contact:	Andrei Kuchynski <akuchynski@...omium.org>
+Description:	Lists the modes supported by the port, ordered by their
+		activation priority. It defines the preferred sequence for activating
+		modes such as Displayport alt-mode, Thunderbolt alt-mode and USB4 mode.
+		The default order can be modified by writing a new sequence to this
+		attribute. Any modes omitted from a user-provided list will be
+		automatically placed at the end of the list.
+
+		Example values:
+		- "USB4 TBT DP": default priority order
+		- "USB4 DP TBT": modified priority order after writing "USB4 DP TBT" or
+			"USB4 DP"
+		- "DP": the port only supports Displayport alt-mode
+
 USB Type-C partner devices (eg. /sys/class/typec/port0-partner/)
 
 What:		/sys/class/typec/<port>-partner/accessory_mode
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.c b/drivers/usb/typec/class.c
index a72325ff099a..93eadbcdd4c0 100644
--- a/drivers/usb/typec/class.c
+++ b/drivers/usb/typec/class.c
@@ -19,6 +19,7 @@
 #include "bus.h"
 #include "class.h"
 #include "pd.h"
+#include "mode_selection.h"
 
 static DEFINE_IDA(typec_index_ida);
 
@@ -540,7 +541,7 @@ static void typec_altmode_release(struct device *dev)
 }
 
 const struct device_type typec_altmode_dev_type = {
-	.name = "typec_alternate_mode",
+	.name = ALTERNATE_MODE_DEVICE_TYPE_NAME,
 	.groups = typec_altmode_groups,
 	.release = typec_altmode_release,
 };
@@ -1942,6 +1943,25 @@ static ssize_t orientation_show(struct device *dev,
 }
 static DEVICE_ATTR_RO(orientation);
 
+static ssize_t mode_priorities_store(struct device *dev,
+			       struct device_attribute *attr,
+			       const char *buf, size_t size)
+{
+	struct typec_port *port = to_typec_port(dev);
+	int ret = typec_mode_priorities_set(port, buf);
+
+	return ret ? : size;
+}
+
+static ssize_t mode_priorities_show(struct device *dev,
+			      struct device_attribute *attr, char *buf)
+{
+	struct typec_port *port = to_typec_port(dev);
+
+	return typec_mode_priorities_get(port, buf);
+}
+static DEVICE_ATTR_RW(mode_priorities);
+
 static struct attribute *typec_attrs[] = {
 	&dev_attr_data_role.attr,
 	&dev_attr_power_operation_mode.attr,
@@ -1954,6 +1974,7 @@ static struct attribute *typec_attrs[] = {
 	&dev_attr_port_type.attr,
 	&dev_attr_orientation.attr,
 	&dev_attr_usb_capability.attr,
+	&dev_attr_mode_priorities.attr,
 	NULL,
 };
 
@@ -1992,6 +2013,9 @@ static umode_t typec_attr_is_visible(struct kobject *kobj,
 			return 0;
 		if (!port->ops || !port->ops->default_usb_mode_set)
 			return 0444;
+	} else if (attr == &dev_attr_mode_priorities.attr) {
+		if (!port->alt_mode_override)
+			return 0;
 	}
 
 	return attr->mode;
@@ -2652,6 +2676,8 @@ struct typec_port *typec_register_port(struct device *parent,
 	else if (cap->usb_capability & USB_CAPABILITY_USB2)
 		port->usb_mode = USB_MODE_USB2;
 
+	typec_mode_priorities_set(port, "");
+
 	device_initialize(&port->dev);
 	port->dev.class = &typec_class;
 	port->dev.parent = parent;
diff --git a/drivers/usb/typec/class.h b/drivers/usb/typec/class.h
index f05d9201c233..28b3c19a0632 100644
--- a/drivers/usb/typec/class.h
+++ b/drivers/usb/typec/class.h
@@ -5,6 +5,7 @@
 
 #include <linux/device.h>
 #include <linux/usb/typec.h>
+#include <linux/usb/typec_altmode.h>
 
 struct typec_mux;
 struct typec_switch;
@@ -82,6 +83,7 @@ struct typec_port {
 	struct device			*usb3_dev;
 
 	bool				alt_mode_override;
+	int				mode_priority_list[TYPEC_MODE_MAX];
 };
 
 #define to_typec_port(_dev_) container_of(_dev_, struct typec_port, dev)
@@ -111,4 +113,6 @@ static inline int typec_link_ports(struct typec_port *connector) { return 0; }
 static inline void typec_unlink_ports(struct typec_port *connector) { }
 #endif
 
+#define ALTERNATE_MODE_DEVICE_TYPE_NAME "typec_alternate_mode"
+
 #endif /* __USB_TYPEC_CLASS__ */
diff --git a/drivers/usb/typec/mode_selection.c b/drivers/usb/typec/mode_selection.c
new file mode 100644
index 000000000000..cb7ddf679037
--- /dev/null
+++ b/drivers/usb/typec/mode_selection.c
@@ -0,0 +1,116 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright 2025 Google LLC.
+ */
+
+#include <linux/usb/typec_altmode.h>
+#include <linux/vmalloc.h>
+#include "mode_selection.h"
+#include "class.h"
+
+static const char * const mode_names[] = {
+	[TYPEC_DP_ALTMODE] = "DP",
+	[TYPEC_TBT_ALTMODE] = "TBT",
+	[TYPEC_USB4_MODE] = "USB4",
+};
+static const char * const default_priorities = "USB4 TBT DP";
+
+/* -------------------------------------------------------------------------- */
+/* port 'mode_priorities' attribute */
+static int typec_mode_parse_priority_string(const char *str, int *list)
+{
+	const bool user_settings = list[0] == TYPEC_MODE_MAX;
+	char *buf, *ptr;
+	char *token;
+	int ret = 0;
+
+	buf = vmalloc(strlen(str) + 1);
+	if (!buf)
+		return -ENOMEM;
+	for (int i = 0; i <= strlen(str); i++)
+		buf[i] = (str[i] == '\n') ? '\0' : str[i];
+	ptr = buf;
+
+	while ((token = strsep(&ptr, " ")) && !ret) {
+		if (strlen(token)) {
+			int mode = 0;
+
+			while ((mode < TYPEC_MODE_MAX) &&
+				strcmp(token, mode_names[mode]))
+				mode++;
+			if (mode == TYPEC_MODE_MAX) {
+				ret = -EINVAL;
+				continue;
+			}
+
+			for (int i = 0; i < TYPEC_MODE_MAX; i++) {
+				if (list[i] == TYPEC_MODE_MAX) {
+					list[i] = mode;
+					break;
+				}
+				if (list[i] == mode) {
+					if (user_settings)
+						ret = -EINVAL;
+					break;
+				}
+			}
+		}
+	}
+	vfree(buf);
+
+	return ret;
+}
+
+int typec_mode_priorities_set(struct typec_port *port,
+		const char *user_priorities)
+{
+	int list[TYPEC_MODE_MAX];
+	int ret;
+
+	for (int i = 0; i < TYPEC_MODE_MAX; i++)
+		list[i] = TYPEC_MODE_MAX;
+
+	ret = typec_mode_parse_priority_string(user_priorities, list);
+	if (!ret)
+		ret = typec_mode_parse_priority_string(default_priorities, list);
+
+	if (!ret)
+		for (int i = 0; i < TYPEC_MODE_MAX; i++)
+			port->mode_priority_list[i] = list[i];
+
+	return ret;
+}
+
+static int port_altmode_supported(struct device *dev, void *data)
+{
+	if (!strcmp(dev->type->name, ALTERNATE_MODE_DEVICE_TYPE_NAME)) {
+		struct typec_altmode *alt = to_typec_altmode(dev);
+
+		if (*(int *)data == typec_svid_to_altmode(alt->svid))
+			return 1;
+	}
+	return 0;
+}
+
+static bool port_mode_supported(struct typec_port *port, int mode)
+{
+	if (mode >= TYPEC_MODE_MAX)
+		return false;
+	if (mode == TYPEC_USB4_MODE)
+		return !!(port->cap->usb_capability & USB_CAPABILITY_USB4);
+	return device_for_each_child(&port->dev, &mode, port_altmode_supported);
+}
+
+int typec_mode_priorities_get(struct typec_port *port, char *buf)
+{
+	ssize_t count = 0;
+
+	for (int i = 0; i < TYPEC_MODE_MAX; i++) {
+		int mode = port->mode_priority_list[i];
+
+		if (port_mode_supported(port, mode))
+			count += sysfs_emit_at(buf, count, "%s ", mode_names[mode]);
+	}
+
+	return count + sysfs_emit_at(buf, count, "\n");
+}
diff --git a/drivers/usb/typec/mode_selection.h b/drivers/usb/typec/mode_selection.h
new file mode 100644
index 000000000000..c595c84e26a4
--- /dev/null
+++ b/drivers/usb/typec/mode_selection.h
@@ -0,0 +1,19 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#include <linux/usb/typec_dp.h>
+#include <linux/usb/typec_tbt.h>
+
+static inline int typec_svid_to_altmode(const u16 svid)
+{
+	switch (svid) {
+	case USB_TYPEC_DP_SID:
+		return TYPEC_DP_ALTMODE;
+	case USB_TYPEC_TBT_SID:
+		return TYPEC_TBT_ALTMODE;
+	}
+	return TYPEC_MODE_MAX;
+}
+
+int typec_mode_priorities_set(struct typec_port *port,
+		const char *user_priorities);
+int typec_mode_priorities_get(struct typec_port *port, char *buf);
diff --git a/include/linux/usb/typec_altmode.h b/include/linux/usb/typec_altmode.h
index b3c0866ea70f..4f05c5f5c91d 100644
--- a/include/linux/usb/typec_altmode.h
+++ b/include/linux/usb/typec_altmode.h
@@ -145,6 +145,13 @@ enum {
 
 #define TYPEC_MODAL_STATE(_state_)	((_state_) + TYPEC_STATE_MODAL)
 
+enum {
+	TYPEC_DP_ALTMODE = 0,
+	TYPEC_TBT_ALTMODE,
+	TYPEC_USB4_MODE,
+	TYPEC_MODE_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);
-- 
2.50.0.727.gbf7dc18ff4-goog

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