[PATCH] soc: qcom: pmic_glink_altmode: Fix SVID=DP && unconnected edge case

[Konrad Dybcio <konradybcio@kernel.org>]

From: Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>

The commit referenced in Fixes started evaluating the value of
alt_port->mux_ctrl before checking the active SVID. This led to
drm_aux_hpd_bridge_notify() no longer being called for the 'DP unplug'
case.

Perhaps somewhat interestingly, the firmware sends a notification with
SVID=DP, mux_ctrl=MUX_CTRL_STATE_NO_CONN and pin_assignment=0 on
unplug. 'pin_assignment' was previously interpreted as a bitfield
excerpt from the second byte of the DP pg_altmode payload (and stored
as an u8).

That value is used in pmic_glink_altmode_sc8280xp_notify(), decremented
by 1 (DPAM_HPD_A). Previously, this would result in an u8 underflow
that would rollover to 0xff (which prior to the Fixes patch would have
caused a pmic_glink_altmode_safe() and 'disconnected' bridge
notification). That check was removed, without a replacement.

Resolve this issue by making sure the SID=DP && mux_ctrl=NO_CONN combo
once again results in a HPD bridge notification.

Fixes: 0539c5a6fdef ("soc: qcom: pmic_glink_altmode: Consume TBT3/USB4 mode notifications")
Reported-by: Abel Vesa <abel.vesa@oss.qualcomm.com>
Tested-by: Abel Vesa <abel.vesa@oss.qualcomm.com>
Signed-off-by: Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>
---
 drivers/soc/qcom/pmic_glink_altmode.c | 18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/drivers/soc/qcom/pmic_glink_altmode.c b/drivers/soc/qcom/pmic_glink_altmode.c
index d0afdcb96ee1..b496b88842a2 100644
--- a/drivers/soc/qcom/pmic_glink_altmode.c
+++ b/drivers/soc/qcom/pmic_glink_altmode.c
@@ -350,15 +350,17 @@ static void pmic_glink_altmode_worker(struct work_struct *work)
 
 	typec_switch_set(alt_port->typec_switch, alt_port->orientation);
 
-	if (alt_port->mux_ctrl == MUX_CTRL_STATE_NO_CONN) {
-		pmic_glink_altmode_safe(altmode, alt_port);
-	} else if (alt_port->svid == USB_TYPEC_TBT_SID) {
+	if (alt_port->svid == USB_TYPEC_TBT_SID) {
 		pmic_glink_altmode_enable_tbt(altmode, alt_port);
 	} else if (alt_port->svid == USB_TYPEC_DP_SID) {
-		pmic_glink_altmode_enable_dp(altmode, alt_port,
-					     alt_port->mode,
-					     alt_port->hpd_state,
-					     alt_port->hpd_irq);
+		if (alt_port->mux_ctrl == MUX_CTRL_STATE_NO_CONN) {
+			pmic_glink_altmode_safe(altmode, alt_port);
+		} else {
+			pmic_glink_altmode_enable_dp(altmode, alt_port,
+						     alt_port->mode,
+						     alt_port->hpd_state,
+						     alt_port->hpd_irq);
+		}
 
 		if (alt_port->hpd_state)
 			conn_status = connector_status_connected;
@@ -368,6 +370,8 @@ static void pmic_glink_altmode_worker(struct work_struct *work)
 		drm_aux_hpd_bridge_notify(&alt_port->bridge->dev, conn_status);
 	} else if (alt_port->mux_ctrl == MUX_CTRL_STATE_TUNNELING) {
 		pmic_glink_altmode_enable_usb4(altmode, alt_port);
+	} else if (alt_port->mux_ctrl == MUX_CTRL_STATE_NO_CONN) {
+		pmic_glink_altmode_safe(altmode, alt_port);
 	} else {
 		pmic_glink_altmode_enable_usb(altmode, alt_port);
 	}

---
base-commit: fc7b1a72c6cd5cbbd989c6c32a6486e3e4e3594d
change-id: 20260306-topic-pgaltmode_fixup-6b488960e355

Best regards,
-- 
Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>