linux-kernel - [PATCH 06/10] Revert "usb: typec: displayport: Receive DP Status Update NAK request exit dp altmode"

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Message-ID: <20250616133147.1835939-7-akuchynski@chromium.org>
Date: Mon, 16 Jun 2025 13:31:43 +0000
From: Andrei Kuchynski <akuchynski@...omium.org>
To: Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
	Dmitry Baryshkov <lumag@...nel.org>,
	Abhishek Pandit-Subedi <abhishekpandit@...omium.org>,
	Jameson Thies <jthies@...gle.com>,
	Benson Leung <bleung@...omium.org>,
	Tzung-Bi Shih <tzungbi@...nel.org>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Guenter Roeck <groeck@...omium.org>,
	Pooja Katiyar <pooja.katiyar@...el.com>,
	Badhri Jagan Sridharan <badhri@...gle.com>,
	RD Babiera <rdbabiera@...gle.com>,
	linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	chrome-platform@...ts.linux.dev,
	Andrei Kuchynski <akuchynski@...omium.org>
Subject: [PATCH 06/10] Revert "usb: typec: displayport: Receive DP Status Update NAK request exit dp altmode"

This reverts commit b4b38ffb38c91afd4dc387608db26f6fc34ed40b.

The commit introduced a deadlock with the cros_ec_typec driver.
The deadlock occurs due to a recursive lock acquisition of
`cros_typec_altmode_work::mutex`.
The call chain is as follows: 
1. cros_typec_altmode_work() acquires the mutex
2. typec_altmode_vdm() -> dp_altmode_vdm() ->
3. typec_altmode_exit() -> cros_typec_altmode_exit()
4. cros_typec_altmode_exit() attempts to acquire the mutex again

This revert is considered safe as no other known driver sends back
DP_CMD_STATUS_UPDATE command with the NAK flag.

Signed-off-by: Andrei Kuchynski <akuchynski@...omium.org>
---
 drivers/usb/typec/altmodes/displayport.c | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/drivers/usb/typec/altmodes/displayport.c b/drivers/usb/typec/altmodes/displayport.c
index b09b58d7311d..ac84a6d64c2f 100644
--- a/drivers/usb/typec/altmodes/displayport.c
+++ b/drivers/usb/typec/altmodes/displayport.c
@@ -393,10 +393,6 @@ static int dp_altmode_vdm(struct typec_altmode *alt,
 		break;
 	case CMDT_RSP_NAK:
 		switch (cmd) {
-		case DP_CMD_STATUS_UPDATE:
-			if (typec_altmode_exit(alt))
-				dev_err(&dp->alt->dev, "Exit Mode Failed!\n");
-			break;
 		case DP_CMD_CONFIGURE:
 			dp->data.conf = 0;
 			ret = dp_altmode_configured(dp);
-- 
2.50.0.rc1.591.g9c95f17f64-goog