[PATCH] 8250: Allow user to force 16550A UART and avoid probing.
From: Richard W.M. Jones
Date: Thu Apr 28 2016 - 18:08:54 EST
Currently autoconf spends 25ms (on my laptop) testing the UART.
Allow the user to avoid this delay if they know that all serial ports
(eg on a virtual machine) are ordinary 16550A. The user does this by
passing '8250_base.really_16550a' on the command line.
Signed-off-by: Richard W.M. Jones <rjones@xxxxxxxxxx>
---
drivers/tty/serial/8250/8250_port.c | 10 ++++++++++
1 file changed, 10 insertions(+)
diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index 00ad2637..ac92f55 100644
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -53,6 +53,10 @@
#define DEBUG_AUTOCONF(fmt...) do { } while (0)
#endif
+static bool really_16550a;
+module_param(really_16550a, bool, 0644);
+MODULE_PARM_DESC(really_16550a, "Don't probe, assume 16550A");
+
#define BOTH_EMPTY (UART_LSR_TEMT | UART_LSR_THRE)
/*
@@ -1171,6 +1175,12 @@ static void autoconfig(struct uart_8250_port *up)
if (!port->iobase && !port->mapbase && !port->membase)
return;
+ if (really_16550a) {
+ up->port.type = PORT_16550A;
+ up->capabilities |= UART_CAP_FIFO;
+ return;
+ }
+
DEBUG_AUTOCONF("ttyS%d: autoconf (0x%04lx, 0x%p): ",
serial_index(port), port->iobase, port->membase);
--
2.7.4
--
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
virt-p2v converts physical machines to virtual machines. Boot with a
live CD or over the network (PXE) and turn machines into KVM guests.
http://libguestfs.org/virt-v2v