Hi Jani
The auto check bot told me the alignment is wrong. So I fixed the
alignment.
```
-:77: CHECK:PARENTHESIS_ALIGNMENT: Alignment should match open parenthesis
#77: FILE: drivers/gpu/drm/i915/display/intel_dp_aux.c:545:
+ ret = intel_dp_aux_xfer_with_recovery(intel_dp, txbuf,
txsize,
+ rxbuf, rxsize,
flags);
-:88: CHECK:PARENTHESIS_ALIGNMENT: Alignment should match open parenthesis
#88: FILE: drivers/gpu/drm/i915/display/intel_dp_aux.c:568:
+ ret = intel_dp_aux_xfer_with_recovery(intel_dp, txbuf,
txsize,
+ rxbuf, rxsize,
flags);
```
BR
An
On Tue, May 5, 2026 at 4:02 PM Jani Nikula <[email protected]>
wrote:
> On Tue, 05 May 2026, ChunAn Wu <[email protected]> wrote:
> > When Fn+F4 triggers mirror mode, the BIOS/EC reconfigures a TC port
> > mode (e.g. DP-Alt to TBT-Alt via UCSI) without generating HPD. The
> > driver's cached TC mode becomes stale, so intel_dp_aux_xfer() uses
> > the wrong power domain and IO routing, and AUX transactions fail.
> >
> > This occurs when the USB-C-to-HDMI dongle does not support TBT, so
> > the mode switch creates a mismatch. It also occurs with slow monitors
> > whose delayed HPD/DDC/EDID recovery causes the Type-C layer to settle
> > on a stale tbt-alt state before the dongle finishes re-negotiation.
> >
> > Add intel_tc_port_aux_recover() to detect hardware/cached TC mode
> > divergence and reset the PHY. Wrap it with
> > intel_dp_aux_xfer_with_recovery() to retry with corrected settings.
> >
> > Tested on Panther Lake and Lunar Lake with a BenQ HDMI monitor via
> > USB-C-to-HDMI dongle.
>
> What are the changes between v1 and v2?
>
> >
> > Signed-off-by: ChunAn Wu <[email protected]>
> > ---
> > drivers/gpu/drm/i915/display/intel_dp_aux.c | 41 +++++++++--
> > drivers/gpu/drm/i915/display/intel_tc.c | 75 +++++++++++++++++++++
> > drivers/gpu/drm/i915/display/intel_tc.h | 1 +
> > 3 files changed, 113 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/display/intel_dp_aux.c
> b/drivers/gpu/drm/i915/display/intel_dp_aux.c
> > index b20ec3e589fa..d496b2231656 100644
> > --- a/drivers/gpu/drm/i915/display/intel_dp_aux.c
> > +++ b/drivers/gpu/drm/i915/display/intel_dp_aux.c
> > @@ -481,6 +481,39 @@ static u32 intel_dp_aux_xfer_flags(const struct
> drm_dp_aux_msg *msg)
> > return 0;
> > }
> >
> > +/**
> > + * intel_dp_aux_xfer_with_recovery - AUX transfer with TC port recovery
> > + * @intel_dp: the DP port
> > + * @send: buffer of bytes to send
> > + * @send_bytes: number of bytes to send
> > + * @recv: buffer to store received reply
> > + * @recv_size: maximum number of bytes to receive
> > + * @aux_send_ctl_flags: extra flags for the AUX send control register
> > + *
> > + * Wrapper around intel_dp_aux_xfer() that attempts to recover from an
> > + * external TC port mode change (e.g., dp-alt -> tbt-alt via hotkey BIOS
> > + * action) when the initial AUX transfer fails. On failure, recovery is
> > + * attempted once via intel_tc_port_aux_recover() before retrying.
> > + *
> > + * Returns: number of received bytes on success, negative error code on
> failure.
> > + */
> > +static int
> > +intel_dp_aux_xfer_with_recovery(struct intel_dp *intel_dp,
> > + const u8 *send, int send_bytes,
> > + u8 *recv, int recv_size,
> > + u32 aux_send_ctl_flags)
> > +{
> > + struct intel_digital_port *dig_port = dp_to_dig_port(intel_dp);
> > + int ret;
> > +
> > + ret = intel_dp_aux_xfer(intel_dp, send, send_bytes, recv,
> recv_size,
> > + aux_send_ctl_flags);
> > + if (ret < 0 && intel_tc_port_aux_recover(dig_port))
> > + ret = intel_dp_aux_xfer(intel_dp, send, send_bytes, recv,
> > + recv_size, aux_send_ctl_flags);
> > + return ret;
> > +}
> > +
> > static ssize_t
> > intel_dp_aux_transfer(struct drm_dp_aux *aux, struct drm_dp_aux_msg
> *msg)
> > {
> > @@ -508,8 +541,8 @@ intel_dp_aux_transfer(struct drm_dp_aux *aux, struct
> drm_dp_aux_msg *msg)
> > if (msg->buffer)
> > memcpy(txbuf + HEADER_SIZE, msg->buffer,
> msg->size);
> >
> > - ret = intel_dp_aux_xfer(intel_dp, txbuf, txsize,
> > - rxbuf, rxsize, flags);
> > + ret = intel_dp_aux_xfer_with_recovery(intel_dp, txbuf,
> txsize,
> > + rxbuf, rxsize,
> flags);
> > if (ret > 0) {
> > msg->reply = rxbuf[0] >> 4;
> >
> > @@ -531,8 +564,8 @@ intel_dp_aux_transfer(struct drm_dp_aux *aux, struct
> drm_dp_aux_msg *msg)
> > if (drm_WARN_ON(display->drm, rxsize > 20))
> > return -E2BIG;
> >
> > - ret = intel_dp_aux_xfer(intel_dp, txbuf, txsize,
> > - rxbuf, rxsize, flags);
> > + ret = intel_dp_aux_xfer_with_recovery(intel_dp, txbuf,
> txsize,
> > + rxbuf, rxsize,
> flags);
> > if (ret > 0) {
> > msg->reply = rxbuf[0] >> 4;
> > /*
> > diff --git a/drivers/gpu/drm/i915/display/intel_tc.c
> b/drivers/gpu/drm/i915/display/intel_tc.c
> > index a21dd4e3fe4c..1b23161e4eea 100644
> > --- a/drivers/gpu/drm/i915/display/intel_tc.c
> > +++ b/drivers/gpu/drm/i915/display/intel_tc.c
> > @@ -1861,6 +1861,81 @@ void intel_tc_port_link_cancel_reset_work(struct
> intel_digital_port *dig_port)
> > cancel_delayed_work(&tc->link_reset_work);
> > }
> >
> > +/**
> > + * intel_tc_port_aux_recover - Recover AUX channel after external TC
> mode change
> > + * @dig_port: digital port
> > + *
> > + * When firmware causes a TC port mode change (e.g., dp-alt ->
> disconnect ->
> > + * tbt-alt) during a hotkey-triggered display mode switch, AUX
> transactions
> > + * using the stale power domain and IO flags will fail with timeouts or
> errors.
> > + * This happens because:
> > + *
> > + * 1. The display driver holds the TC link in dp-alt mode
> (link_refcount > 0)
> > + * 2. Firmware (e.g., via HP WMI hotkey BIOS action) reconfigures the
> TC port
> > + * mode externally without notifying the display driver
> > + * 3. tc->mode stays as TC_PORT_DP_ALT while HW transitions to a
> different
> > + * mode, invalidating the AUX power domain and IO flags used by
> > + * intel_dp_aux_xfer()
> > + *
> > + * This function detects the discrepancy between tc->mode and actual HW
> state,
> > + * and re-synchronizes them via a TC PHY reset. After recovery, AUX
> retries
> > + * will use the correct power domain and control flags.
> > + *
> > + * The link_refcount is temporarily cleared to allow
> intel_tc_port_reset_mode()
> > + * to proceed without the PHY-ownership assertion that fires when
> link_refcount
> > + * is non-zero and firmware has already released PHY ownership.
> > + *
> > + * Must be called outside the TC port lock (tc->lock).
> > + *
> > + * Returns: %true if recovery was performed and AUX can be retried,
> > + * %false if recovery was not needed or not possible.
> > + */
> > +bool intel_tc_port_aux_recover(struct intel_digital_port *dig_port)
> > +{
> > + struct intel_tc_port *tc;
> > + struct intel_display *display;
> > + bool recovered = false;
> > +
> > + if (!intel_encoder_is_tc(&dig_port->base))
> > + return false;
> > +
> > + tc = to_tc_port(dig_port);
> > + display = to_intel_display(dig_port);
> > +
> > + mutex_lock(&tc->lock);
> > +
> > + /*
> > + * Recovery is only needed when the link is actively held AND the
> HW
> > + * TC mode has diverged from the driver's cached state.
> > + */
> > + if (!tc->link_refcount || !intel_tc_port_needs_reset(tc))
> > + goto out;
> > +
> > + drm_dbg_kms(display->drm,
> > + "Port %s: AUX recover: external TC mode change
> detected (%s -> HW), reconnecting TC PHY\n",
> > + tc->port_name, tc_port_mode_name(tc->mode));
> > +
> > + /*
> > + * Temporarily clear link_refcount so intel_tc_port_reset_mode()
> can
> > + * run the PHY disconnect/connect cycle without the ownership
> assertion
> > + * that fires when link_refcount > 0 and firmware has already
> released
> > + * PHY ownership externally.
> > + */
> > + tc->link_refcount = 0;
> > + intel_tc_port_reset_mode(tc, 1, false);
> > + tc->link_refcount = 1;
> > +
> > + recovered = tc->mode != TC_PORT_DISCONNECTED;
> > + if (!recovered)
> > + drm_warn(display->drm,
> > + "Port %s: AUX recover: failed to restore TC port
> mode\n",
> > + tc->port_name);
> > +
> > +out:
> > + mutex_unlock(&tc->lock);
> > + return recovered;
> > +}
> > +
> > static void __intel_tc_port_lock(struct intel_tc_port *tc,
> > int required_lanes)
> > {
> > diff --git a/drivers/gpu/drm/i915/display/intel_tc.h
> b/drivers/gpu/drm/i915/display/intel_tc.h
> > index 6719aea5bd58..d44998a3081a 100644
> > --- a/drivers/gpu/drm/i915/display/intel_tc.h
> > +++ b/drivers/gpu/drm/i915/display/intel_tc.h
> > @@ -108,6 +108,7 @@ bool intel_tc_port_ref_held(struct
> intel_digital_port *dig_port);
> > bool intel_tc_port_link_needs_reset(struct intel_digital_port
> *dig_port);
> > bool intel_tc_port_link_reset(struct intel_digital_port *dig_port);
> > void intel_tc_port_link_cancel_reset_work(struct intel_digital_port
> *dig_port);
> > +bool intel_tc_port_aux_recover(struct intel_digital_port *dig_port);
> >
> > int intel_tc_port_init(struct intel_digital_port *dig_port, bool
> is_legacy);
> > void intel_tc_port_cleanup(struct intel_digital_port *dig_port);
>
> --
> Jani Nikula, Intel
>
