linux-kernel - Re: [PATCH v2 2/2] usb: typec: altmodes/displayport: do not enter mode if port is the UFP

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Message-ID: <20260110075345.238333-1-andyshrk@163.com>
Date: Sat, 10 Jan 2026 15:53:42 +0800
From: Andy Yan <andyshrk@....com>
To: rdbabiera@...gle.com
Cc: badhri@...gle.com,
	gregkh@...uxfoundation.org,
	heikki.krogerus@...ux.intel.com,
	linux-kernel@...r.kernel.org,
	linux-usb@...r.kernel.org,
	andyshrk@....com,
	sebastian.reichel@...labora.com
Subject: Re: [PATCH v2 2/2] usb: typec: altmodes/displayport: do not enter mode if port is the UFP

>Nothing currently stops the DisplayPort Alt Mode driver from sending
>Enter Mode if the port is the Data Device. Utilize
>typec_altmode_get_data_role to prevent mode entry.

>---
> drivers/usb/typec/altmodes/displayport.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)

>diff --git a/drivers/usb/typec/altmodes/displayport.c b/drivers/usb/typec/altmodes/displayport.c
>index 1dcb77faf85d..8d111ad3b71b 100644
>--- a/drivers/usb/typec/altmodes/displayport.c
>+++ b/drivers/usb/typec/altmodes/displayport.c
>@@ -758,7 +758,9 @@ int dp_altmode_probe(struct typec_altmode *alt)
> 	struct fwnode_handle *fwnode;
> 	struct dp_altmode *dp;
> 
>-	/* FIXME: Port can only be DFP_U. */
>+	/* Port can only be DFP_U. */
>+	if (typec_altmode_get_data_role(alt) != TYPEC_HOST)
>+		return -EPROTO;
> 
> 	/* Make sure we have compatible pin configurations */
> 	if (!(DP_CAP_PIN_ASSIGN_DFP_D(port->vdo) &
>
I found that after applying this patch, the Rock 5B SBC can no longer
enter alt mode when connected to a DP monitor via a Type-C hub, the following
error dmesg can be seen:
typec_displayport port0-partner.0: probe with driver typec_displayport failed with error -71

The TypeC Port on rock5b drive via the PD chip FUSB302
# cat /sys/kernel/debug/usb/tcpm-4-0022/log 
[    1.561397] Unable to find pd-revision property or incorrect array size
[    1.590115] Setting usb_comm capable false
[    1.590123] Setting voltage/current limit 0 mV 0 mA
[    1.590129] polarity 0
[    1.590198] Requesting mux state 0, usb-role 0, orientation 0
[    1.631710] state change INVALID_STATE -> SNK_UNATTACHED [rev1 NONE_AMS]
[    1.633129] CC1: 0 -> 0, CC2: 0 -> 0 [state SNK_UNATTACHED, polarity 0, disconnected]
[    1.645221] 4-0022: registered
[    1.646189] Setting usb_comm capable false
[    1.646215] Setting voltage/current limit 0 mV 0 mA
[    1.646231] polarity 0
[    1.646237] Requesting mux state 0, usb-role 0, orientation 0
[    1.662091] cc:=2
[    1.668000] pending state change PORT_RESET -> PORT_RESET_WAIT_OFF @ 100 ms [rev1 NONE_AMS]
[    1.671183] state change PORT_RESET -> PORT_RESET_WAIT_OFF [delayed 100 ms]
[    1.672491] pending state change PORT_RESET_WAIT_OFF -> SNK_UNATTACHED @ 920 ms [rev1 NONE_AMS]
[    2.601879] state change PORT_RESET_WAIT_OFF -> SNK_UNATTACHED [delayed 920 ms]
[    2.602431] Start toggling
[    2.624387] CC1: 0 -> 0, CC2: 0 -> 5 [state TOGGLING, polarity 0, connected]
[    2.626056] state change TOGGLING -> SNK_ATTACH_WAIT [rev1 NONE_AMS]
[    2.629010] pending state change SNK_ATTACH_WAIT -> SNK_DEBOUNCED @ 200 ms [rev1 NONE_AMS]
[    2.830604] state change SNK_ATTACH_WAIT -> SNK_DEBOUNCED [delayed 200 ms]
[    2.831984] state change SNK_DEBOUNCED -> SNK_ATTACHED [rev1 NONE_AMS]
[    2.832941] polarity 1
[    2.832945] Requesting mux state 1, usb-role 2, orientation 2
[    2.860029] state change SNK_ATTACHED -> SNK_STARTUP [rev1 NONE_AMS]
[    2.861402] state change SNK_STARTUP -> SNK_DISCOVERY [rev3 NONE_AMS]
[    2.861945] Setting voltage/current limit 5000 mV 3000 mA
[    2.861950] vbus=0 charge:=1
[    2.862859] state change SNK_DISCOVERY -> SNK_WAIT_CAPABILITIES [rev3 NONE_AMS]
[    2.869362] pending state change SNK_WAIT_CAPABILITIES -> SNK_SOFT_RESET @ 310 ms [rev3 NONE_AMS]
[    3.181014] state change SNK_WAIT_CAPABILITIES -> SNK_SOFT_RESET [delayed 310 ms]
[    3.181580] AMS SOFT_RESET_AMS start
[    3.183145] state change SNK_SOFT_RESET -> AMS_START [rev3 SOFT_RESET_AMS]
[    3.184513] state change AMS_START -> SOFT_RESET_SEND [rev3 SOFT_RESET_AMS]
[    3.185066] PD TX, header: 0x8d
[    3.193733] PD TX complete, status: 0
[    3.196440] pending state change SOFT_RESET_SEND -> HARD_RESET_SEND @ 60 ms [rev3 SOFT_RESET_AMS]
[    3.198922] PD RX, header: 0x1a3 [1]
[    3.200603] AMS SOFT_RESET_AMS finished
[    3.202836] state change SOFT_RESET_SEND -> SNK_WAIT_CAPABILITIES [rev3 NONE_AMS]
[    3.207907] pending state change SNK_WAIT_CAPABILITIES -> SNK_WAIT_CAPABILITIES_TIMEOUT @ 310 ms [rev3 NONE_AMS]
[    3.208976] PD RX, header: 0x43a1 [1]
[    3.210464]  PDO 0: type 0, 5000 mV, 2000 mA [RUDE]
[    3.210467]  PDO 1: type 0, 9000 mV, 2450 mA []
[    3.210469]  PDO 2: type 0, 15000 mV, 2670 mA []
[    3.210472]  PDO 3: type 0, 20000 mV, 3000 mA []
[    3.211607] state change SNK_WAIT_CAPABILITIES -> SNK_NEGOTIATE_CAPABILITIES [rev3 POWER_NEGOTIATION]
[    3.213865] Setting usb_comm capable true
[    3.213871] cc=2 cc1=0 cc2=5 vbus=0 vconn=sink polarity=1
[    3.213877] Requesting PDO 3: 20000 mV, 3000 mA
[    3.213880] PD TX, header: 0x1282
[    3.222930] PD TX complete, status: 0
[    3.225674] pending state change SNK_NEGOTIATE_CAPABILITIES -> HARD_RESET_SEND @ 60 ms [rev3 POWER_NEGOTIATION]
[    3.229457] PD RX, header: 0x5a3 [1]
[    3.232125] state change SNK_NEGOTIATE_CAPABILITIES -> SNK_TRANSITION_SINK [rev3 POWER_NEGOTIATION]
[    3.234275] Setting standby current 5000 mV @ 500 mA
[    3.234278] Setting voltage/current limit 5000 mV 500 mA
[    3.235158] pending state change SNK_TRANSITION_SINK -> HARD_RESET_SEND @ 500 ms [rev3 POWER_NEGOTIATION]
[    3.339971] PD RX, header: 0x7a6 [1]
[    3.341738] Setting voltage/current limit 20000 mV 3000 mA
[    3.342566] state change SNK_TRANSITION_SINK -> SNK_READY [rev3 POWER_NEGOTIATION]
[    3.346462] AMS POWER_NEGOTIATION finished
[    3.352068] AMS DISCOVER_IDENTITY start
[    3.354952] PD TX, header: 0x148f
[    3.363951] PD TX complete, status: 0
[    3.372273] PD RX, header: 0x59af [1]
[    3.375213] Rx VDM cmd 0xff00a041 type 1 cmd 1 len 5
[    3.376489] AMS DISCOVER_IDENTITY finished
[    3.378482] Identity: 1d5c:7102.070a
[    3.381145] AMS DISCOVER_SVIDS start
[    3.384002] PD TX, header: 0x168f
[    3.393019] PD TX complete, status: 0
[    3.400228] PD RX, header: 0x2baf [1]
[    3.403143] Rx VDM cmd 0xff00a042 type 1 cmd 2 len 2
[    3.404418] AMS DISCOVER_SVIDS finished
[    3.405753] SVID 1: 0xff01
[    3.408814] AMS DISCOVER_MODES start
[    3.411666] PD TX, header: 0x188f
[    3.420681] PD TX complete, status: 0
[    3.427868] PD RX, header: 0x2daf [1]
[    3.430784] Rx VDM cmd 0xff01a043 type 1 cmd 3 len 2
[    3.432193] AMS DISCOVER_MODES finished
[    3.433811]  Alternate mode 0: SVID 0xff01, VDO 1: 0x00040045
[    3.468873] AMS DFP_TO_UFP_ENTER_MODE start
[    3.473347] PD TX, header: 0x1a8f
[    3.483714] PD TX complete, status: 0
[    3.490564] PD RX, header: 0x1faf [1]
[    3.493540] Rx VDM cmd 0xff01a144 type 1 cmd 4 len 1
[    3.495653] AMS DFP_TO_UFP_ENTER_MODE finished
[    3.501550] AMS STRUCTURED_VDMS start
[    3.504410] PD TX, header: 0x2c8f
[    3.513803] PD TX complete, status: 0
[    3.520991] PD RX, header: 0x21af [1]
[    3.523920] Rx VDM cmd 0xff01a150 type 1 cmd 16 len 2
[    3.526044] AMS STRUCTURED_VDMS finished
[    3.544870] AMS STRUCTURED_VDMS start
[    3.547736] PD TX, header: 0x2e8f
[    3.557132] PD TX complete, status: 0
[    3.564509] PD RX, header: 0x13af [1]
[    3.567452] Rx VDM cmd 0xff01a151 type 1 cmd 17 len 1
[    3.569581] AMS STRUCTURED_VDMS finished
[    6.927982] PD RX, header: 0x25af [1]
[    6.931501] Rx VDM cmd 0xff01a106 type 0 cmd 6 len 2

The flow terminates at this point without continuing into alt mode.

After reverting this patch, the process can continue and successfully enter alt mode:

[    3.159202] AMS DFP_TO_UFP_ENTER_MODE start
[    3.159207] PD TX, header: 0x1a8f
[    3.167022] PD TX complete, status: 0
[    3.171317] PD RX, header: 0x1faf [1]
[    3.171322] Rx VDM cmd 0xff01a144 type 1 cmd 4 len 1
[    3.171327] AMS DFP_TO_UFP_ENTER_MODE finished
[    3.171402] AMS STRUCTURED_VDMS start
[    3.171406] PD TX, header: 0x2c8f
[    3.179592] PD TX complete, status: 0
[    3.184266] PD RX, header: 0x21af [1]
[    3.184271] Rx VDM cmd 0xff01a150 type 1 cmd 16 len 2
[    3.184277] AMS STRUCTURED_VDMS finished
[    3.184315] AMS STRUCTURED_VDMS start
[    3.184319] PD TX, header: 0x2e8f
[    3.192595] PD TX complete, status: 0
[    3.196953] PD RX, header: 0x13af [1]
[    3.196959] Rx VDM cmd 0xff01a151 type 1 cmd 17 len 1
[    3.196966] AMS STRUCTURED_VDMS finished
[    6.562035] PD RX, header: 0x25af [1]
[    6.562044] Rx VDM cmd 0xff01a106 type 0 cmd 6 len 2
-- 
2.43.0