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@chromium.org>
---
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-googHi Andrei,
On Thu, Aug 14, 2025 at 06:44:54PM +0000, Andrei Kuchynski wrote:
> 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.
I think this needs to be simplified. You don't need this elaborate
implementation in the beginning.
I'm going to do some suggestions. I don't know if all of them work,
but hopefully you get the idea how I would like to see the initial
support to be implemented.
> Signed-off-by: Andrei Kuchynski <akuchynski@chromium.org>
> ---
> 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;
I'm not sure we need this.
> };
>
> #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",
> +};
You only need string for USB4. The altmode names come from the drivers.
> +static const int default_priorities[TYPEC_ALTMODE_MAX] = {
> + [TYPEC_ALTMODE_DP] = 2,
> + [TYPEC_ALTMODE_TBT] = 1,
> + [TYPEC_ALTMODE_USB4] = 0,
> +};
The default priorities is an array of svids. And I really think that
the highest priority should be 1 not 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;
> +}
Get rid of this.
> +/**
> + * 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;
> +};
Get rid of this. I don't see why you would need to separate the
priority handling at this point. Keep it as simply as possible first.
Just place the priority member to struct typec_altmode. 0 should
indicate that there is no specific priority set, or default order
should be used IMO.
> +/* -------------------------------------------------------------------------- */
> +/* 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;
Just support every altmode bind to a driver and USB4. USB4 you
identify with a specific usb4 device type.
> + 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
I would suggest that you create a separate patch or patches for the
USB4 mode registration.
> +enum typec_mode_type {
> + TYPEC_ALTMODE_DP = 0,
> + TYPEC_ALTMODE_TBT,
> + TYPEC_ALTMODE_USB4,
> + TYPEC_ALTMODE_MAX,
> +};
Drop this completely.
thanks,
--
heikki
Hi again,
On Thu, Aug 21, 2025 at 01:09:57PM +0300, Heikki Krogerus wrote:
> > 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",
> > +};
>
> You only need string for USB4. The altmode names come from the drivers.
Sorry, that won't work with port altmode. But you can still do the
lookup with just the sid.
<snip>
> > +/* -------------------------------------------------------------------------- */
> > +/* 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;
>
> Just support every altmode bind to a driver and USB4. USB4 you
> identify with a specific usb4 device type.
No driver so you would need to use the mode_names, but instead of
doing that, just don't limit this at all.
If there is no name for the mode, use the svid.
thanks,
--
heikki
On Thu, Aug 21, 2025 at 1:15 PM Heikki Krogerus
<heikki.krogerus@linux.intel.com> wrote:
>
> Hi again,
>
> On Thu, Aug 21, 2025 at 01:09:57PM +0300, Heikki Krogerus wrote:
> > > 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",
> > > +};
> >
> > You only need string for USB4. The altmode names come from the drivers.
>
> Sorry, that won't work with port altmode. But you can still do the
> lookup with just the sid.
>
Hi Heikki,
I can get names from altmode partner. Names are only needed to
provide results of entering the mode. No partner - no results.
>
> I think this needs to be simplified. You don't need this elaborate
> implementation in the beginning.
>
> I'm going to do some suggestions. I don't know if all of them work,
> but hopefully you get the idea how I would like to see the initial
> support to be implemented.
>
I checked your suggestions. It looks like all of them should
work. Thank you!
- priority is a member to struct typec_altmode
- use svid instead of enum typec_mode_type
- no list or other variables in struct typec_port.
- struct mode_selection_state will be introduced in other series
>
> The default priorities is an array of svids. And I really think that
> the highest priority should be 1 not 0.
>
I think your idea of setting priorities based on the order of
port altmod registrations is better. We don't really need default
priorities in this case.
>
> No driver so you would need to use the mode_names, but instead of
> doing that, just don't limit this at all.
>
> If there is no name for the mode, use the svid.
>
> thanks,
>
> --
> heikki
What if we later create typec_USB4 driver, similar to the
existing typec_displayport and typec_thunderbolt?
This approach could unify how various modes are handled,
eliminating exceptions for USB4 or any other mode.
The port altmode would contain priority and support "enter" and
"exit" operations, while partner altmode would handle "activate"
and name field. I've explored this approach with cros_ec_typec
driver, and it appears to be a promising way to manage USB4 as
alternate mode.
Thanks,
Andrei
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