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
