[PATCH v2 02/22] usb: typec: Represent USB4 on the Type-C bus
Sven Peter
sven at kernel.org
Sun Sep 6 11:36:25 PDT 2026
USB4 technically isn't alternate mode and entered using the EUDO and has
no SVID or Discover Modes Response. We can still represent it like an
altmode on the Type-C bus though by adding a mode kind. Exclude the USB4
modes from any SVID-specific operations and driver binding, but allow
consumers to observe their state through notifications.
Like for other altmodes, expose the USB4 mode to sysfs: Add a mode_kind
to be able to differentiate and then expose the EUDO, make the USB4
active state read-only since we only represent firmware-negotiated USB4
modes and omit anything that only applies to SVID-specific altmodes.
Signed-off-by: Sven Peter <sven at kernel.org>
---
Hope it's fine to add you as the contact for the sysfs documentation,
happy to add myself otherwise though.
---
Documentation/ABI/testing/sysfs-bus-typec | 36 ++++++++++++++
drivers/usb/typec/bus.c | 67 ++++++++++++++++++++-----
drivers/usb/typec/class.c | 83 +++++++++++++++++++++++++++----
drivers/usb/typec/mode_selection.c | 6 ++-
include/linux/usb/typec.h | 20 +++++++-
include/linux/usb/typec_altmode.h | 10 +++-
6 files changed, 193 insertions(+), 29 deletions(-)
diff --git a/Documentation/ABI/testing/sysfs-bus-typec b/Documentation/ABI/testing/sysfs-bus-typec
index 205d9c91e2e1..524bbcbadf64 100644
--- a/Documentation/ABI/testing/sysfs-bus-typec
+++ b/Documentation/ABI/testing/sysfs-bus-typec
@@ -12,6 +12,35 @@ Description:
Valid values are boolean.
+ For USB4 mode devices this attribute is read-only. On a port it
+ indicates whether USB4 support is enabled; on a partner it reports
+ whether USB4 is active. USB4 entry and exit are controlled by the
+ port controller. Partner state changes notify this attribute and
+ generate KOBJ_CHANGE uevents.
+
+What: /sys/bus/typec/devices/.../mode_kind
+Date: September 2026
+Contact: Heikki Krogerus <heikki.krogerus at linux.intel.com>
+Description:
+ Read-only protocol kind represented by this mode device:
+ "altmode" for an SVID-specific alternate mode, or "usb4" for
+ USB4 negotiated using Enter_USB.
+
+ USB4 devices do not expose svid, mode, vdo, or priority
+ attributes, or the legacy modeN attribute group. USB4 partner
+ uevents contain MODE_KIND=usb4 instead of SVID, MODE, and
+ MODALIAS variables.
+
+What: /sys/bus/typec/devices/.../eudo
+Date: September 2026
+Contact: Heikki Krogerus <heikki.krogerus at linux.intel.com>
+Description:
+ Read-only Enter_USB Data Object (EUDO), formatted as
+ 0x followed by eight hexadecimal digits. Present only on USB4
+ partner mode devices, not on ports or SVID-specific alternate
+ modes. USB4 cable information is encoded in the EUDO; there are
+ no USB4 cable plug mode devices.
+
What: /sys/bus/typec/devices/.../description
Date: July 2018
Contact: Heikki Krogerus <heikki.krogerus at linux.intel.com>
@@ -36,6 +65,8 @@ Description:
the mode index is not assigned, identifying the alternate mode
must be done with either mode VDO or the description.
+ This attribute is not present on USB4 mode devices.
+
What: /sys/bus/typec/devices/.../svid
Date: July 2018
Contact: Heikki Krogerus <heikki.krogerus at linux.intel.com>
@@ -43,9 +74,14 @@ Description:
The Standard or Vendor ID (SVID) assigned by USB-IF for this
alternate mode.
+ This attribute is not present on USB4 mode devices.
+
What: /sys/bus/typec/devices/.../vdo
Date: July 2018
Contact: Heikki Krogerus <heikki.krogerus at linux.intel.com>
Description:
Shows the VDO in hexadecimal returned by Discover Modes command
for this mode.
+
+ This attribute is not present on USB4 mode devices. USB4 partner
+ mode devices expose the EUDO in the eudo attribute.
diff --git a/drivers/usb/typec/bus.c b/drivers/usb/typec/bus.c
index e84b134a3381..8e6d7769fac3 100644
--- a/drivers/usb/typec/bus.c
+++ b/drivers/usb/typec/bus.c
@@ -93,6 +93,8 @@ int typec_altmode_notify(struct typec_altmode *adev,
if (!adev)
return 0;
+ if (adev->mode_kind != TYPEC_MODE_KIND_ALTMODE)
+ return -EOPNOTSUPP;
altmode = to_altmode(adev);
@@ -125,12 +127,19 @@ EXPORT_SYMBOL_GPL(typec_altmode_notify);
*/
int typec_altmode_enter(struct typec_altmode *adev, u32 *vdo)
{
- struct altmode *partner = to_altmode(adev)->partner;
- struct typec_altmode *pdev = &partner->adev;
+ struct typec_altmode *pdev;
+ struct altmode *partner;
int ret;
- if (!adev || adev->active)
+ if (!adev)
return 0;
+ if (adev->mode_kind != TYPEC_MODE_KIND_ALTMODE)
+ return -EOPNOTSUPP;
+ if (adev->active)
+ return 0;
+
+ partner = to_altmode(adev)->partner;
+ pdev = &partner->adev;
if (!pdev->ops || !pdev->ops->enter)
return -EOPNOTSUPP;
@@ -156,12 +165,19 @@ EXPORT_SYMBOL_GPL(typec_altmode_enter);
*/
int typec_altmode_exit(struct typec_altmode *adev)
{
- struct altmode *partner = to_altmode(adev)->partner;
- struct typec_altmode *pdev = &partner->adev;
+ struct typec_altmode *pdev;
+ struct altmode *partner;
int ret;
- if (!adev || !adev->active)
+ if (!adev)
return 0;
+ if (adev->mode_kind != TYPEC_MODE_KIND_ALTMODE)
+ return -EOPNOTSUPP;
+ if (!adev->active)
+ return 0;
+
+ partner = to_altmode(adev)->partner;
+ pdev = &partner->adev;
if (!pdev->ops || !pdev->ops->exit)
return -EOPNOTSUPP;
@@ -185,8 +201,13 @@ EXPORT_SYMBOL_GPL(typec_altmode_exit);
*/
int typec_altmode_attention(struct typec_altmode *adev, u32 vdo)
{
- struct altmode *partner = to_altmode(adev)->partner;
struct typec_altmode *pdev;
+ struct altmode *partner;
+
+ if (adev->mode_kind != TYPEC_MODE_KIND_ALTMODE)
+ return -EOPNOTSUPP;
+
+ partner = to_altmode(adev)->partner;
if (!partner)
return -ENODEV;
@@ -219,6 +240,8 @@ int typec_altmode_vdm(struct typec_altmode *adev,
if (!adev)
return 0;
+ if (adev->mode_kind != TYPEC_MODE_KIND_ALTMODE)
+ return -EOPNOTSUPP;
altmode = to_altmode(adev);
@@ -258,12 +281,17 @@ EXPORT_SYMBOL_GPL(typec_altmode_get_partner);
*/
int typec_cable_altmode_enter(struct typec_altmode *adev, enum typec_plug_index sop, u32 *vdo)
{
- struct altmode *partner = to_altmode(adev)->partner;
struct typec_altmode *pdev;
+ struct altmode *partner;
- if (!adev || adev->active)
+ if (!adev)
+ return 0;
+ if (adev->mode_kind != TYPEC_MODE_KIND_ALTMODE)
+ return -EOPNOTSUPP;
+ if (adev->active)
return 0;
+ partner = to_altmode(adev)->partner;
if (!partner)
return -ENODEV;
@@ -288,12 +316,17 @@ EXPORT_SYMBOL_GPL(typec_cable_altmode_enter);
*/
int typec_cable_altmode_exit(struct typec_altmode *adev, enum typec_plug_index sop)
{
- struct altmode *partner = to_altmode(adev)->partner;
struct typec_altmode *pdev;
+ struct altmode *partner;
- if (!adev || !adev->active)
+ if (!adev)
+ return 0;
+ if (adev->mode_kind != TYPEC_MODE_KIND_ALTMODE)
+ return -EOPNOTSUPP;
+ if (!adev->active)
return 0;
+ partner = to_altmode(adev)->partner;
if (!partner)
return -ENODEV;
@@ -326,6 +359,8 @@ int typec_cable_altmode_vdm(struct typec_altmode *adev, enum typec_plug_index so
if (!adev)
return 0;
+ if (adev->mode_kind != TYPEC_MODE_KIND_ALTMODE)
+ return -EOPNOTSUPP;
altmode = to_altmode(adev);
@@ -422,7 +457,8 @@ struct typec_altmode *typec_match_altmode(struct typec_altmode **altmodes,
for (i = 0; i < n; i++) {
if (!altmodes[i])
break;
- if (altmodes[i]->svid == svid && altmodes[i]->mode == mode)
+ if (altmodes[i]->mode_kind == TYPEC_MODE_KIND_ALTMODE &&
+ altmodes[i]->svid == svid && altmodes[i]->mode == mode)
return altmodes[i];
}
@@ -472,6 +508,10 @@ static int typec_match(struct device *dev, const struct device_driver *driver)
if (!is_typec_partner_altmode(dev))
return 0;
+ /* USB4 mode devices report firmware state through notifiers only. */
+ if (altmode->mode_kind != TYPEC_MODE_KIND_ALTMODE)
+ return 0;
+
for (id = drv->id_table; id->svid; id++)
if (id->svid == altmode->svid)
return 1;
@@ -485,6 +525,9 @@ static int typec_uevent(const struct device *dev, struct kobj_uevent_env *env)
if (!is_typec_partner_altmode(dev))
return 0;
+ if (altmode->mode_kind == TYPEC_MODE_KIND_USB4)
+ return add_uevent_var(env, "MODE_KIND=usb4");
+
if (add_uevent_var(env, "SVID=%04X", altmode->svid))
return -ENOMEM;
diff --git a/drivers/usb/typec/class.c b/drivers/usb/typec/class.c
index 5808a3ef0d6c..869d6857c0dc 100644
--- a/drivers/usb/typec/class.c
+++ b/drivers/usb/typec/class.c
@@ -233,23 +233,24 @@ static const char * const usb_modes[] = {
static int altmode_match(struct device *dev, const void *data)
{
struct typec_altmode *adev = to_typec_altmode(dev);
- const struct typec_device_id *id = data;
+ const struct typec_altmode *match = data;
if (!is_typec_port_altmode(dev))
return 0;
- return (adev->svid == id->svid);
+ if (adev->mode_kind != match->mode_kind)
+ return 0;
+ return adev->mode_kind == TYPEC_MODE_KIND_USB4 || adev->svid == match->svid;
}
static void typec_altmode_set_partner(struct altmode *altmode)
{
struct typec_altmode *adev = &altmode->adev;
- struct typec_device_id id = { adev->svid };
struct typec_port *port = typec_altmode2port(adev);
struct altmode *partner;
struct device *dev;
- dev = device_find_child(&port->dev, &id, altmode_match);
+ dev = device_find_child(&port->dev, adev, altmode_match);
if (!dev)
return;
@@ -296,6 +297,8 @@ static void typec_altmode_put_partner(struct altmode *altmode)
*
* If a partner or cable plug executes Enter/Exit Mode command successfully, the
* drivers use this routine to report the updated state of the mode.
+ * For USB4 partner modes, drivers use this routine to report entry through
+ * Enter_USB and exit from USB4.
*/
void typec_altmode_update_active(struct typec_altmode *adev, bool active)
{
@@ -319,8 +322,10 @@ void typec_altmode_update_active(struct typec_altmode *adev, bool active)
active ? TYPEC_ALTMODE_ENTERED :
TYPEC_ALTMODE_EXITED,
adev);
- snprintf(dir, sizeof(dir), "mode%d", adev->mode);
- sysfs_notify(&adev->dev.kobj, dir, "active");
+ if (adev->mode_kind == TYPEC_MODE_KIND_ALTMODE) {
+ snprintf(dir, sizeof(dir), "mode%d", adev->mode);
+ sysfs_notify(&adev->dev.kobj, dir, "active");
+ }
sysfs_notify(&adev->dev.kobj, NULL, "active");
kobject_uevent(&adev->dev.kobj, KOBJ_CHANGE);
}
@@ -502,13 +507,30 @@ svid_show(struct device *dev, struct device_attribute *attr, char *buf)
}
static DEVICE_ATTR_RO(svid);
+static ssize_t mode_kind_show(struct device *dev, struct device_attribute *attr,
+ char *buf)
+{
+ struct typec_altmode *adev = to_typec_altmode(dev);
+
+ return sysfs_emit(buf, "%s\n",
+ adev->mode_kind == TYPEC_MODE_KIND_USB4 ? "usb4" : "altmode");
+}
+static DEVICE_ATTR_RO(mode_kind);
+
+static ssize_t eudo_show(struct device *dev, struct device_attribute *attr, char *buf)
+{
+ return sysfs_emit(buf, "0x%08x\n", to_typec_altmode(dev)->eudo);
+}
+static DEVICE_ATTR_RO(eudo);
+
static int increment_duplicated_priority(struct device *dev, void *data)
{
if (is_typec_port_altmode(dev)) {
struct typec_altmode **alt_target = (struct typec_altmode **)data;
struct typec_altmode *alt = to_typec_altmode(dev);
- if (alt != *alt_target && alt->priority == (*alt_target)->priority) {
+ if (alt->mode_kind == TYPEC_MODE_KIND_ALTMODE &&
+ alt != *alt_target && alt->priority == (*alt_target)->priority) {
alt->priority++;
*alt_target = alt;
return 1;
@@ -523,7 +545,8 @@ static int find_duplicated_priority(struct device *dev, void *data)
struct typec_altmode **alt_target = (struct typec_altmode **)data;
struct typec_altmode *alt = to_typec_altmode(dev);
- if (alt != *alt_target && alt->priority == (*alt_target)->priority)
+ if (alt->mode_kind == TYPEC_MODE_KIND_ALTMODE &&
+ alt != *alt_target && alt->priority == (*alt_target)->priority)
return 1;
}
return 0;
@@ -579,6 +602,8 @@ static ssize_t priority_show(struct device *dev,
static DEVICE_ATTR_RW(priority);
static struct attribute *typec_altmode_attrs[] = {
+ &dev_attr_mode_kind.attr,
+ &dev_attr_eudo.attr,
&dev_attr_active.attr,
&dev_attr_mode.attr,
&dev_attr_svid.attr,
@@ -593,6 +618,18 @@ static umode_t typec_altmode_attr_is_visible(struct kobject *kobj,
struct typec_altmode *adev = to_typec_altmode(kobj_to_dev(kobj));
struct typec_port *port = typec_altmode2port(adev);
+ if (adev->mode_kind == TYPEC_MODE_KIND_USB4) {
+ if (attr == &dev_attr_svid.attr || attr == &dev_attr_mode.attr ||
+ attr == &dev_attr_vdo.attr || attr == &dev_attr_priority.attr)
+ return 0;
+ if (attr == &dev_attr_eudo.attr && !is_typec_partner(adev->dev.parent))
+ return 0;
+ if (attr == &dev_attr_active.attr)
+ return 0444;
+ } else if (attr == &dev_attr_eudo.attr) {
+ return 0;
+ }
+
if (attr == &dev_attr_active.attr) {
if (!is_typec_port(adev->dev.parent)) {
if (!port->mode_control || !adev->ops || !adev->ops->activate)
@@ -698,20 +735,33 @@ typec_register_altmode(struct device *parent,
const struct typec_altmode_desc *desc,
const struct device_type *type)
{
- unsigned int id = altmode_id_get(parent);
bool is_port = is_typec_port(parent);
struct altmode *alt;
+ unsigned int id;
int ret;
+ if (desc->mode_kind != TYPEC_MODE_KIND_ALTMODE &&
+ desc->mode_kind != TYPEC_MODE_KIND_USB4)
+ return ERR_PTR(-EINVAL);
+ if (desc->mode_kind == TYPEC_MODE_KIND_USB4 &&
+ (desc->svid || desc->mode || is_typec_plug(parent)))
+ return ERR_PTR(-EINVAL);
+
+ id = altmode_id_get(parent);
+
alt = kzalloc_obj(*alt);
if (!alt) {
altmode_id_remove(parent, id);
return ERR_PTR(-ENOMEM);
}
+ alt->adev.mode_kind = desc->mode_kind;
alt->adev.svid = desc->svid;
alt->adev.mode = desc->mode;
- alt->adev.vdo = desc->vdo;
+ if (desc->mode_kind == TYPEC_MODE_KIND_USB4)
+ alt->adev.eudo = desc->eudo;
+ else
+ alt->adev.vdo = desc->vdo;
alt->adev.mode_selection = desc->mode_selection;
alt->roles = desc->roles;
alt->id = id;
@@ -730,7 +780,8 @@ typec_register_altmode(struct device *parent,
sprintf(alt->group_name, "mode%d", desc->mode);
alt->group.name = alt->group_name;
alt->group.attrs = alt->attrs;
- alt->groups[0] = &alt->group;
+ if (desc->mode_kind == TYPEC_MODE_KIND_ALTMODE)
+ alt->groups[0] = &alt->group;
alt->adev.dev.parent = parent;
alt->adev.dev.groups = alt->groups;
@@ -1110,6 +1161,10 @@ EXPORT_SYMBOL_GPL(typec_partner_set_num_altmodes);
* SVID listed in response to Discover Modes command need to be listed in an
* array in @desc.
*
+ * For USB4, set @desc->mode_kind to %TYPEC_MODE_KIND_USB4 and @desc->eudo to the
+ * EUDO and leave SVID and mode zero. USB4 devices expose firmware state
+ * through notifications and do not bind alternate-mode drivers.
+ *
* Returns handle to the alternate mode on success or ERR_PTR on failure.
*/
struct typec_altmode *
@@ -2698,6 +2753,9 @@ EXPORT_SYMBOL_GPL(typec_get_fw_cap);
* This routine is used to register an alternate mode that @port is capable of
* supporting.
*
+ * For USB4, set @desc->mode_kind to %TYPEC_MODE_KIND_USB4 and leave SVID and
+ * mode zero. Register it before the USB4 partner mode, which carries the EUDO.
+ *
* Returns handle to the alternate mode on success or ERR_PTR on failure.
*/
struct typec_altmode *
@@ -2727,6 +2785,9 @@ typec_port_register_altmode(struct typec_port *port,
to_altmode(adev)->mux = mux;
to_altmode(adev)->retimer = retimer;
+ if (adev->mode_kind == TYPEC_MODE_KIND_USB4)
+ return adev;
+
ret = typec_mode_set_priority(adev, 0);
if (ret) {
typec_unregister_altmode(adev);
diff --git a/drivers/usb/typec/mode_selection.c b/drivers/usb/typec/mode_selection.c
index cd376f67e445..5e378deed5c2 100644
--- a/drivers/usb/typec/mode_selection.c
+++ b/drivers/usb/typec/mode_selection.c
@@ -66,7 +66,8 @@ static int activate_altmode(struct device *dev, void *data)
struct typec_altmode *alt = to_typec_altmode(dev);
struct mode_order *order = (struct mode_order *)data;
- if (order->svid == alt->svid) {
+ if (alt->mode_kind == TYPEC_MODE_KIND_ALTMODE &&
+ order->svid == alt->svid) {
if (alt->ops && alt->ops->activate)
order->result = alt->ops->activate(alt, order->enter);
else
@@ -215,7 +216,8 @@ static int altmode_add_to_list(struct device *dev, void *data)
const struct typec_altmode *pdev = typec_altmode_get_partner(altmode);
struct mode_state *ms;
- if (pdev && altmode->ops && altmode->ops->activate) {
+ if (altmode->mode_kind == TYPEC_MODE_KIND_ALTMODE &&
+ pdev && altmode->ops && altmode->ops->activate) {
ms = kzalloc_obj(*ms);
if (!ms)
return -ENOMEM;
diff --git a/include/linux/usb/typec.h b/include/linux/usb/typec.h
index 914a6f0844c5..add2c1368774 100644
--- a/include/linux/usb/typec.h
+++ b/include/linux/usb/typec.h
@@ -138,11 +138,23 @@ struct usb_pd_identity {
int typec_partner_set_identity(struct typec_partner *partner);
int typec_cable_set_identity(struct typec_cable *cable);
+/**
+ * enum typec_mode_kind - Protocol represented by a Type-C mode device
+ * @TYPEC_MODE_KIND_ALTMODE: SVID-specific alternate mode (the default)
+ * @TYPEC_MODE_KIND_USB4: USB4, negotiated using Enter_USB
+ */
+enum typec_mode_kind {
+ TYPEC_MODE_KIND_ALTMODE,
+ TYPEC_MODE_KIND_USB4,
+};
+
/*
* struct typec_altmode_desc - USB Type-C Alternate Mode Descriptor
* @svid: Standard or Vendor ID
* @mode: Index of the Mode
- * @vdo: VDO returned by Discover Modes USB PD command
+ * @vdo: Discover Modes VDO for SVID-specific alternate modes
+ * @eudo: Enter_USB Data Object for USB4 partner modes
+ * @mode_kind: Protocol kind; SVID and mode are unused for USB4
* @roles: Only for ports. DRP if the mode is available in both roles
* @inactive: Only for ports. Make this port inactive (default is active).
*
@@ -152,11 +164,15 @@ int typec_cable_set_identity(struct typec_cable *cable);
struct typec_altmode_desc {
u16 svid;
u8 mode;
- u32 vdo;
+ union {
+ u32 vdo;
+ u32 eudo;
+ };
/* Only used with ports */
enum typec_port_data roles;
bool inactive;
bool mode_selection;
+ enum typec_mode_kind mode_kind;
};
void typec_partner_set_pd_revision(struct typec_partner *partner, u16 pd_revision);
diff --git a/include/linux/usb/typec_altmode.h b/include/linux/usb/typec_altmode.h
index ef21ead551be..8d31e35e9320 100644
--- a/include/linux/usb/typec_altmode.h
+++ b/include/linux/usb/typec_altmode.h
@@ -24,7 +24,9 @@ struct typec_altmode_ops;
* @dev: Driver model's view of this device
* @svid: Standard or Vendor ID (SVID) of the alternate mode
* @mode: Index of the Mode
- * @vdo: VDO returned by Discover Modes USB PD command
+ * @vdo: Discover Modes VDO for SVID-specific alternate modes
+ * @eudo: Enter_USB Data Object for USB4 partner modes
+ * @mode_kind: Protocol kind; SVID and mode are unused for USB4
* @active: Tells has the mode been entered or not
* @priority: Priority used by the automatic alternate mode selection process
* @mode_selection: Whether entry to this alternate mode is managed by the
@@ -37,7 +39,11 @@ struct typec_altmode {
struct device dev;
u16 svid;
int mode;
- u32 vdo;
+ union {
+ u32 vdo;
+ u32 eudo;
+ };
+ enum typec_mode_kind mode_kind;
unsigned int active:1;
u8 priority;
bool mode_selection;
--
2.55.0
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