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[PATCH] xen/uart: set a default baudrate if non specified neither found
- To: xen-devel@xxxxxxxxxxxxxxxxxxxx
- From: Roger Pau Monne <roger.pau@xxxxxxxxxx>
- Date: Mon, 30 Mar 2026 17:03:50 +0200
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- Cc: Roger Pau Monne <roger.pau@xxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>, Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>
- Delivery-date: Mon, 30 Mar 2026 15:04:13 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
If the user has set baudrate as "auto" (use whatever was configured) but
Xen cannot find any set baudrate use a default fallback baudrate of
115200.
Otherwise the console will very likely end up being non-functional, as
further values are derived from the baudrate (like the transmit timeout),
and using -1 will result in screwed parameters being derived from the
baudrate.
Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
xen/drivers/char/ns16550.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/xen/drivers/char/ns16550.c b/xen/drivers/char/ns16550.c
index b23e85a3c68b..130e292f057d 100644
--- a/xen/drivers/char/ns16550.c
+++ b/xen/drivers/char/ns16550.c
@@ -346,9 +346,16 @@ static void ns16550_setup_preirq(struct ns16550 *uart)
if ( divisor )
uart->baud = uart->clock_hz / (divisor << 4);
else
+ {
+ uart->baud = 115200;
printk(XENLOG_ERR
"Automatic baud rate determination was requested,"
- " but a baud rate was not set up\n");
+ " but a baud rate was not set up\n"
+ "Setting baudrate to %u\n", uart->baud);
+ divisor = uart->clock_hz / (uart->baud << 4);
+ ns_write_reg(uart, UART_DLL, (uint8_t)divisor);
+ ns_write_reg(uart, UART_DLM, (uint8_t)(divisor >> 8));
+ }
}
ns_write_reg(uart, UART_LCR, lcr);
--
2.51.0
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