[PATCH v2] usb: typec: altmodes/displayport: verify compatible source/sink role combination

[RD Babiera]

DisplayPort Alt Mode CTS test 10.3.8 states that both sides of the
connection shall be compatible with one another such that the connection
is not Source to Source or Sink to Sink.

The DisplayPort driver currently checks for a compatible pin configuration
that resolves into a source and sink combination. The CTS test is designed
to send a Discover Modes message that has a compatible pin configuration
but advertises the same port capability as the device; the current check
fails this.

Verify that the port and port partner resolve into a valid source and sink
combination before checking for a compatible pin configuration.

---
Changes since v1:
* Fixed styling errors
* Added DP_CAP_IS_UFP_D and DP_CAP_IS_DFP_D as macros to typec_dp.h
---

Fixes: 0e3bb7d6894d ("usb: typec: Add driver for DisplayPort alternate mode")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: RD Babiera <rdbabiera@xxxxxxxxxx>
---
 drivers/usb/typec/altmodes/displayport.c | 5 +++++
 include/linux/usb/typec_dp.h             | 2 ++
 2 files changed, 7 insertions(+)

diff --git a/drivers/usb/typec/altmodes/displayport.c b/drivers/usb/typec/altmodes/displayport.c
index 718da02036d8..9c17955da570 100644
--- a/drivers/usb/typec/altmodes/displayport.c
+++ b/drivers/usb/typec/altmodes/displayport.c
@@ -578,6 +578,11 @@ int dp_altmode_probe(struct typec_altmode *alt)
 
 	/* FIXME: Port can only be DFP_U. */
 
+	/* Make sure that the port and partner can resolve into source and sink */
+	if (!(DP_CAP_IS_DFP_D(port->vdo) && DP_CAP_IS_UFP_D(alt->vdo)) &&
+	    !(DP_CAP_IS_UFP_D(port->vdo) && DP_CAP_IS_DFP_D(alt->vdo)))
+		return -ENODEV;
+
 	/* Make sure we have compatiple pin configurations */
 	if (!(DP_CAP_PIN_ASSIGN_DFP_D(port->vdo) &
 	      DP_CAP_PIN_ASSIGN_UFP_D(alt->vdo)) &&
diff --git a/include/linux/usb/typec_dp.h b/include/linux/usb/typec_dp.h
index 1f358098522d..4e6c0479307f 100644
--- a/include/linux/usb/typec_dp.h
+++ b/include/linux/usb/typec_dp.h
@@ -67,6 +67,8 @@ enum {
 #define   DP_CAP_UFP_D			1
 #define   DP_CAP_DFP_D			2
 #define   DP_CAP_DFP_D_AND_UFP_D	3
+#define DP_CAP_IS_UFP_D(_cap_)		(!!(DP_CAP_CAPABILITY(_cap_) & DP_CAP_UFP_D))
+#define DP_CAP_IS_DFP_D(_cap_)		(!!(DP_CAP_CAPABILITY(_cap_) & DP_CAP_DFP_D))
 #define DP_CAP_DP_SIGNALLING(_cap_)	(((_cap_) & GENMASK(5, 2)) >> 2)
 #define   DP_CAP_SIGNALLING_HBR3	1
 #define   DP_CAP_SIGNALLING_UHBR10	2

base-commit: 5220d8b04a840fa09434072c866d032b163419e3
-- 
2.42.0.655.g421f12c284-goog