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>

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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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drivers/usb/typec/altmodes/displayport.c

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