[00/10] USB Type-C mode selection

This patch series introduces a flexible mechanism for USB Type-C mode
selection, enabling into USB4 mode, Thunderbolt alternate mode, or
DisplayPort alternate mode.
Two new sysfs attributes are exposed to provide user control over mode
selection:
`altmode_priorities`: Allows users to define their preferred order for
attempting mode entry.
`mode_selection`: Initiates an automatic mode entry process based on the
configured priorities and reports the outcome.
The mode selection logic attempts to enter prioritized modes sequentially.
A mode is considered successfully negotiated only when its alternate mode
driver explicitly reports a positive status. Alternate mode drivers are
required to report their mode entry status (either successful or failed).
If an alt-mode driver does not report its status within a defined timeout
period, the system automatically proceeds to attempt entry into the next
preferred mode.

This series was tested on a ChromeOS Brya device running kernel 6.6, and on
an Android OS device with kernel 6.12.

Andrei Kuchynski (10):
  usb: typec: Add alt_mode_override field to port property
  platform/chrome: cros_ec_typec: Set alt_mode_override flag
  usb: typec: ucsi: Set alt_mode_override flag
  usb: typec: Expose alternate mode priorities via sysfs
  usb: typec: Implement automated alternate mode selection
  Revert "usb: typec: displayport: Receive DP Status Update NAK request
    exit dp altmode"
  usb: typec: Report altmode entry status via callback
  usb: typec: ucsi: displayport: Propagate DP altmode entry result
  platform/chrome: cros_ec_typec: Propagate altmode entry result
  platform/chrome: cros_ec_typec: Report USB4 mode entry status via
    callback

 Documentation/ABI/testing/sysfs-class-typec  |  34 ++
 drivers/platform/chrome/cros_ec_typec.c      |  11 +
 drivers/platform/chrome/cros_typec_altmode.c |  32 +-
 drivers/platform/chrome/cros_typec_altmode.h |   6 +
 drivers/usb/typec/Makefile                   |   2 +-
 drivers/usb/typec/altmodes/displayport.c     |  17 +-
 drivers/usb/typec/altmodes/thunderbolt.c     |   6 +
 drivers/usb/typec/class.c                    |  95 +++-
 drivers/usb/typec/class.h                    |  16 +
 drivers/usb/typec/mode_selection.c           | 505 +++++++++++++++++++
 drivers/usb/typec/mode_selection.h           |  42 ++
 drivers/usb/typec/ucsi/displayport.c         |   4 +-
 drivers/usb/typec/ucsi/ucsi.c                |   2 +
 include/linux/usb/pd_vdo.h                   |   2 +
 include/linux/usb/typec.h                    |   1 +
 include/linux/usb/typec_altmode.h            |  12 +
 include/linux/usb/typec_dp.h                 |   2 +
 include/linux/usb/typec_tbt.h                |   3 +
 18 files changed, 775 insertions(+), 17 deletions(-)
 create mode 100644 drivers/usb/typec/mode_selection.c
 create mode 100644 drivers/usb/typec/mode_selection.h

On Tue, Jun 17, 2025 at 10:54 AM Heikki Krogerus
<heikki.krogerus@linux.intel.com> wrote:
>
> Hi Andrei,
>
> On Mon, Jun 16, 2025 at 01:31:43PM +0000, Andrei Kuchynski wrote:
> > This reverts commit b4b38ffb38c91afd4dc387608db26f6fc34ed40b.
> >
> > The commit introduced a deadlock with the cros_ec_typec driver.
> > The deadlock occurs due to a recursive lock acquisition of
> > `cros_typec_altmode_work::mutex`.
> > The call chain is as follows:
> > 1. cros_typec_altmode_work() acquires the mutex
> > 2. typec_altmode_vdm() -> dp_altmode_vdm() ->
> > 3. typec_altmode_exit() -> cros_typec_altmode_exit()
> > 4. cros_typec_altmode_exit() attempts to acquire the mutex again
> >
> > This revert is considered safe as no other known driver sends back
> > DP_CMD_STATUS_UPDATE command with the NAK flag.
> >
> > Signed-off-by: Andrei Kuchynski <akuchynski@chromium.org>
> > ---
> >  drivers/usb/typec/altmodes/displayport.c | 4 ----
> >  1 file changed, 4 deletions(-)
> >
> > diff --git a/drivers/usb/typec/altmodes/displayport.c b/drivers/usb/typec/altmodes/displayport.c
> > index b09b58d7311d..ac84a6d64c2f 100644
> > --- a/drivers/usb/typec/altmodes/displayport.c
> > +++ b/drivers/usb/typec/altmodes/displayport.c
> > @@ -393,10 +393,6 @@ static int dp_altmode_vdm(struct typec_altmode *alt,
> >               break;
> >       case CMDT_RSP_NAK:
> >               switch (cmd) {
> > -             case DP_CMD_STATUS_UPDATE:
> > -                     if (typec_altmode_exit(alt))
> > -                             dev_err(&dp->alt->dev, "Exit Mode Failed!\n");
> > -                     break;
>
> Commit b4b38ffb38c9 ("usb: typec: displayport: Receive DP Status
> Update NAK request exit dp altmode") addressed a very real problem
> with failure to execute data role swap. You are not really offering
> anything else for that issue here.

Thanks, I see the problem now. Reverting the patch is not feasible.

>
> Is it not an option to just schedule the mode exit here instead to
> solve the problem?

Of course, that's an option. Alternatively, maybe I could resolve the
deadlock within the `cros_ec_typec` driver. Regardless, this seems like
a separate patch.

>
> diff --git a/drivers/usb/typec/altmodes/displayport.c b/drivers/usb/typec/altmodes/displayport.c
> index b09b58d7311d..2abbe4de3216 100644
> --- a/drivers/usb/typec/altmodes/displayport.c
> +++ b/drivers/usb/typec/altmodes/displayport.c
> @@ -394,8 +394,7 @@ static int dp_altmode_vdm(struct typec_altmode *alt,
>         case CMDT_RSP_NAK:
>                 switch (cmd) {
>                 case DP_CMD_STATUS_UPDATE:
> -                       if (typec_altmode_exit(alt))
> -                               dev_err(&dp->alt->dev, "Exit Mode Failed!\n");
> +                       dp->state = DP_STATE_EXIT;
>                         break;
>                 case DP_CMD_CONFIGURE:
>                         dp->data.conf = 0;
>
>
> --
> heikki