The patch 92d7223a74235054f2aa7227d207d9c57f84dca0 ("alpha: io: reorder
barriers to guarantee writeX() and iowriteX() ordering #2") broke boot on
the Alpha Avanti platform.
The patch changes timing between accesses to the ISA bus, in particular,
it reduces the time between "write" access and a subsequent "read" access.
This causes lock-up when accessing the real time clock and serial ports.
This patch fixes the serial ports by adding a small delay before the "inb"
instruction.
Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
Fixes: 92d7223a7423 ("alpha: io: reorder barriers to guarantee writeX() and iowriteX() ordering #2")
Cc: stable@xxxxxxxxxxxxxxx # v4.17+
---
drivers/tty/serial/8250/8250_port.c | 4 ++++
1 file changed, 4 insertions(+)
Index: linux-stable/drivers/tty/serial/8250/8250_port.c
===================================================================
--- linux-stable.orig/drivers/tty/serial/8250/8250_port.c 2020-05-06 08:25:19.000000000 +0200
+++ linux-stable/drivers/tty/serial/8250/8250_port.c 2020-05-06 09:04:17.000000000 +0200
@@ -442,6 +442,10 @@ static unsigned int mem32be_serial_in(st
static unsigned int io_serial_in(struct uart_port *p, int offset)
{
+#ifdef CONFIG_ALPHA
+/* we need a small delay, the Alpha Avanti chipset locks up with back-to-back accesses */
+ ndelay(300);
+#endif
offset = offset << p->regshift;
return inb(p->iobase + offset);
}
