serial: 8250: Use frame time to determine timeout

Rather than using a hard-coded per-character Tx-timeout of 10ms,
use the frame time to determine a timeout value. The value is
doubled to ensure that a timeout is only hit during unexpected
circumstances.

Since the frame time may not be available during early printing,
the previous 10ms value is kept as a fallback.

Signed-off-by: John Ogness <[email protected]>
Reviewed-by: Petr Mladek <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: jogness

drivers/tty/serial/8250/8250_port.c

@@ -2081,9 +2081,17 @@ static void serial8250_break_ctl(struct uart_port *port, int break_state)
 /* Returns true if @bits were set, false on timeout */
 static bool wait_for_lsr(struct uart_8250_port *up, int bits)
 {
-	unsigned int status, tmout = 10000;
+	unsigned int status, tmout;
+
+	/*
+	 * Wait for a character to be sent. Fallback to a safe default
+	 * timeout value if @frame_time is not available.
+	 */
+	if (up->port.frame_time)
+		tmout = up->port.frame_time * 2 / NSEC_PER_USEC;
+	else
+		tmout = 10000;
 
-	/* Wait up to 10ms for the character(s) to be sent. */
 	for (;;) {
 		status = serial_lsr_in(up);