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: 0e3bb7d6894d ("usb: typec: Add driver for DisplayPort alternate mode")
Cc: stable@vger.kernel.org
Signed-off-by: RD Babiera <rdbabiera@google.com>
Reviewed-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Link: https://lore.kernel.org/r/20230329215159.2046932-1-rdbabiera@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/usb/typec/altmodes/displayport.c b/drivers/usb/typec/altmodes/displayport.c
index 662cd04..8f3e884 100644 (file)
--- a/drivers/usb/typec/altmodes/displayport.c
+++ b/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;