diff mbox series

[tty-next,v5,2/6] serial: 8250: Use frame time to determine timeout

Message ID 20250107212702.169493-3-john.ogness@linutronix.de
State New
Headers show
Series convert 8250 to nbcon | expand

Commit Message

John Ogness Jan. 7, 2025, 9:26 p.m. UTC 
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 <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
---
 drivers/tty/serial/8250/8250_port.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

Comments

Andy Shevchenko Jan. 13, 2025, 9:54 a.m. UTC | #1 
On Tue, Jan 07, 2025 at 10:32:58PM +0106, John Ogness wrote:
> 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.

...

> +	/*
> +	 * 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;

I would use it in a form of

		tmout = 10 * USEC_PER_MSEC;

This will give a hint of the real unit (10 ms in us).
diff mbox series

Patch

diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index 3a946ebe9139..ca8f6f3855eb 100644
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/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);