From c0ae54724ebd989cc7313e9bd13d23118c509197 Mon Sep 17 00:00:00 2001 From: Madhu M Date: Tue, 23 Jun 2026 06:02:15 +0530 Subject: [PATCH] usb: typec: displayport: Reject DP Alt Mode VDO with no pin assignment for its capability Some docks/Type-C dongles expose a malformed DP Capabilities VDO: they claim a DFP_D (source) or UFP_D (sink) capability but leave the corresponding pin assignment field empty. Such a device can never have Alt Mode configured. Currently the driver still proceeds, which is misleading and offers no diagnostic. Per VESA DPAM v2.1a Section 5.4.1 (Table 5-6): Case 1 (receptacle): A DP Source device receptacle (DFP_D) declares its lane routing in the DP Source Pin field (Bits 15:8); a DP Sink device receptacle (UFP_D) declares its lanes in the DP Sink Pin field (Bits 23:16). Case 2 (direct-attach plug): A DP Sink device plug (UFP_D) declares its lane routing in the DP Source Pin field (Bits 15:8), and a DP Source device plug (DFP_D) declares its lanes in the DP Sink Pin field (Bits 23:16). In either case the field holds the supported pin assignment values (e.g. C/D/E); 00000000b means no pin assignment is supported for that capability. Reject such a DP Alt Mode VDO in dp_altmode_probe(): if the claimed capability has no matching pin assignments, fail probe with -ENODEV, releasing the SOP' plug reference on the error path. Signed-off-by: Madhu M Reviewed-by: Andrei Kuchynski Reviewed-by: Heikki Krogerus Link: https://patch.msgid.link/20260623003215.4077711-1-madhu.m@intel.com Signed-off-by: Greg Kroah-Hartman --- drivers/usb/typec/altmodes/displayport.c | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/drivers/usb/typec/altmodes/displayport.c b/drivers/usb/typec/altmodes/displayport.c index 263a89c5f324..2a553cfcf61d 100644 --- a/drivers/usb/typec/altmodes/displayport.c +++ b/drivers/usb/typec/altmodes/displayport.c @@ -764,6 +764,7 @@ int dp_altmode_probe(struct typec_altmode *alt) struct typec_altmode *plug = typec_altmode_get_plug(alt, TYPEC_PLUG_SOP_P); struct fwnode_handle *fwnode; struct dp_altmode *dp; + u32 cap = DP_CAP_CAPABILITY(alt->vdo); /* Port can only be DFP_U. */ if (typec_altmode_get_data_role(alt) != TYPEC_HOST) @@ -778,6 +779,18 @@ int dp_altmode_probe(struct typec_altmode *alt) return -ENODEV; } + /* + * Make sure the DisplayPort VDO is valid (VESA DPAM v2.1a, Section + * 5.4.1, Table 5-6, DP Capabilities VDO). A device exposing DP on a + * USB-C receptacle must advertise at least one pin assignment for the + * capability it claims, otherwise Alt Mode can never be configured. + */ + if ((cap == DP_CAP_DFP_D && !DP_CAP_PIN_ASSIGN_DFP_D(alt->vdo)) || + (cap == DP_CAP_UFP_D && !DP_CAP_PIN_ASSIGN_UFP_D(alt->vdo))) { + typec_altmode_put_plug(plug); + return -ENODEV; + } + dp = devm_kzalloc(&alt->dev, sizeof(*dp), GFP_KERNEL); if (!dp) { typec_altmode_put_plug(plug);