Commit a20dcf53ea98 ("usb: typec: tcpm: Respond Not_Supported if no
snk_vdo"), stops tcpm_pd_data_request() calling tcpm_handle_vdm_request()
when port->nr_snk_vdo is not set. But the VDM might be intended for an
altmode-driver, in which case nr_snk_vdo does not matter.

This change breaks the forwarding of connector hotplug (HPD) events
for displayport altmode on devices which don't set nr_snk_vdo.

tcpm_pd_data_request() is the only caller of tcpm_handle_vdm_request(),
so we can move the nr_snk_vdo check to inside it, at which point we
have already looked up the altmode device so we can check for this too.

Doing this check here also ensures that vdm_state gets set to
VDM_STATE_DONE if it was VDM_STATE_BUSY, even if we end up with
responding with PD_MSG_CTRL_NOT_SUPP later.

Note that tcpm_handle_vdm_request() was already sending
PD_MSG_CTRL_NOT_SUPP in some circumstances, after moving the nr_snk_vdo
check the same error-path is now taken when that check fails. So that
we have only one error-path for this and not two. Replace the
tcpm_queue_message(PD_MSG_CTRL_NOT_SUPP) used by the existing error-path
with the more robust tcpm_pd_handle_msg() from the (now removed) second
error-path.

Fixes: a20dcf53ea98 ("usb: typec: tcpm: Respond Not_Supported if no snk_vdo")
Cc: stable <stable@vger.kernel.org>
Cc: Kyle Tso <kyletso@google.com>
Acked-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Acked-by: Kyle Tso <kyletso@google.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Link: https://lore.kernel.org/r/20210816154632.381968-1-hdegoede@redhat.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>