[PATCH 7.1 181/271] serial: amba-pl011: fix indefinite RS485 post-send delay

7.1-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Fan Wu <[email protected]>

commit dcb2f7576ce460eb4f6b9048b7c266c8da5848a8 upstream.

The RS485 stop hrtimer is used both to drain the transmitter and to wait
out delay_rts_after_send. The callback cannot tell the two apart, so it
restarts the post-send delay on every expiry and the timer never stops.

Add a WAIT_AFTER_SEND_DELAY state so its expiry ends the stop sequence
instead of restarting the delay.

Fixes: 2c1fd53af21b ("serial: amba-pl011: Fix RTS handling in RS485 mode")
Cc: stable <[email protected]>
Assisted-by: Codex:gpt-5.6
Signed-off-by: Fan Wu <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
 drivers/tty/serial/amba-pl011.c |    8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

--- a/drivers/tty/serial/amba-pl011.c
+++ b/drivers/tty/serial/amba-pl011.c
@@ -277,6 +277,7 @@ enum pl011_rs485_tx_state {
 	WAIT_AFTER_RTS,
 	SEND,
 	WAIT_AFTER_SEND,
+	WAIT_AFTER_SEND_DELAY,
 };
 
 /*
@@ -1318,6 +1319,7 @@ static void pl011_rs485_tx_stop(struct u
 			return;
 		}
 		if (port->rs485.delay_rts_after_send > 0) {
+			uap->rs485_tx_state = WAIT_AFTER_SEND_DELAY;
 			hrtimer_start(&uap->trigger_stop_tx,
 				      ms_to_ktime(port->rs485.delay_rts_after_send),
 				      HRTIMER_MODE_REL);
@@ -1383,7 +1385,8 @@ static void pl011_rs485_tx_start(struct
 		uap->rs485_tx_state = SEND;
 		return;
 	}
-	if (uap->rs485_tx_state == WAIT_AFTER_SEND) {
+	if (uap->rs485_tx_state == WAIT_AFTER_SEND ||
+	    uap->rs485_tx_state == WAIT_AFTER_SEND_DELAY) {
 		hrtimer_try_to_cancel(&uap->trigger_stop_tx);
 		uap->rs485_tx_state = SEND;
 		return;
@@ -1450,7 +1453,8 @@ static enum hrtimer_restart pl011_trigge
 	unsigned long flags;
 
 	uart_port_lock_irqsave(&uap->port, &flags);
-	if (uap->rs485_tx_state == WAIT_AFTER_SEND)
+	if (uap->rs485_tx_state == WAIT_AFTER_SEND ||
+	    uap->rs485_tx_state == WAIT_AFTER_SEND_DELAY)
 		pl011_rs485_tx_stop(uap);
 	uart_port_unlock_irqrestore(&uap->port, flags);