usb: typec: altmodes/displayport: Fix configure initial pin assignment

While determining the initial pin assignment to be sent in the configure
message, using the DP_PIN_ASSIGN_DP_ONLY_MASK mask causes the DFP_U to
send both Pin Assignment C and E when both are supported by the DFP_U and
UFP_U. The spec (Table 5-7 DFP_U Pin Assignment Selection Mandates,
VESA DisplayPort Alt Mode Standard v2.0) indicates that the DFP_U never
selects Pin Assignment E when Pin Assignment C is offered.

Update the DP_PIN_ASSIGN_DP_ONLY_MASK conditional to intially select only
Pin Assignment C if it is available.

Fixes: 0e3bb7d ("usb: typec: Add driver for DisplayPort alternate mode")
Cc: [email protected]
Signed-off-by: RD Babiera <[email protected]>
Reviewed-by: Heikki Krogerus <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: RD Babiera

drivers/usb/typec/altmodes/displayport.c

@@ -112,8 +112,12 @@ static int dp_altmode_configure(struct dp_altmode *dp, u8 con)
 		if (dp->data.status & DP_STATUS_PREFER_MULTI_FUNC &&
 		    pin_assign & DP_PIN_ASSIGN_MULTI_FUNC_MASK)
 			pin_assign &= DP_PIN_ASSIGN_MULTI_FUNC_MASK;
-		else if (pin_assign & DP_PIN_ASSIGN_DP_ONLY_MASK)
+		else if (pin_assign & DP_PIN_ASSIGN_DP_ONLY_MASK) {
 			pin_assign &= DP_PIN_ASSIGN_DP_ONLY_MASK;
+			/* Default to pin assign C if available */
+			if (pin_assign & BIT(DP_PIN_ASSIGN_C))
+				pin_assign = BIT(DP_PIN_ASSIGN_C);
+		}
 
 		if (!pin_assign)
 			return -EINVAL;