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usb: typec: displayport: Reject DP Alt Mode VDO with no pin assignment for its capability

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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 <madhu.m@intel.com>
Reviewed-by: Andrei Kuchynski <akuchynski@chromium.org>
Reviewed-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Link: https://patch.msgid.link/20260623003215.4077711-1-madhu.m@intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Madhu M 2026-06-23 06:02:15 +05:30 committed by Greg Kroah-Hartman
parent 8c4871a4fa
commit c0ae54724e
1 changed files with 13 additions and 0 deletions
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13
drivers/usb/typec/altmodes/displayport.c
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@ -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);