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[2001:b011:2008:6553:c5e9:d4dc:67fd:a915]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2b9cae16a9esm114405985ad.50.2026.05.04.20.35.59 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 04 May 2026 20:36:01 -0700 (PDT) From: ChunAn Wu To: Jani Nikula , Rodrigo Vivi , Joonas Lahtinen , Tvrtko Ursulin , David Airlie , Simona Vetter Cc: intel-gfx@lists.freedesktop.org, intel-xe@lists.freedesktop.org, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org Subject: [PATCH v2] drm/i915/tc: Recover AUX channel after external TC port mode change Date: Tue, 5 May 2026 11:35:57 +0800 Message-Id: <20260505033558.157604-1-an.wu@canonical.com> X-Mailer: git-send-email 2.34.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 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. Signed-off-by: ChunAn Wu --- 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); -- 2.34.1