linux-kernel - [PATCH v1] usb: typec: altmodes/displayport: Fix configure initial pin assignment

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Date:   Wed, 29 Mar 2023 21:51:59 +0000
From:   RD Babiera <rdbabiera@...gle.com>
To:     unlisted-recipients:; (no To-header on input)
Cc:     heikki.krogerus@...ux.intel.com, gregkh@...uxfoundation.org,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        RD Babiera <rdbabiera@...gle.com>, stable@...r.kernel.org
Subject: [PATCH v1] 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@...r.kernel.org
Signed-off-by: RD Babiera <rdbabiera@...gle.com>
---
 drivers/usb/typec/altmodes/displayport.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/typec/altmodes/displayport.c b/drivers/usb/typec/altmodes/displayport.c
index 662cd043b50e..8f3e884222ad 100644
--- 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;

base-commit: 97318d6427f62b723c89f4150f8f48126ef74961
-- 
2.40.0.348.gf938b09366-goog