[PATCH] serial: 8250: Reinit port_id when adding back serial8250_isa_devs

[Tony Lindgren <tony@atomide.com>]

After fixing the serial core port device to use port->port_id instead of
port->line, unloading a hardware specific 8250 port driver started
producing an error for "sysfs: cannot create duplicate filename".

This is happening as we are wrongly initializing port->port_id to zero
when adding back serial8250_isa_devs instances, and the serial8250:0.0
sysfs entry may already exist. For serial8250 devices, we typically have
multiple devices mapped to a single driver instance. For the
serial8250_isa_devs instances, the port->port_id is the same as port->line.

Let's fix the issue by re-initializing port_id when adding back the
serial8250_isa_devs instances in serial8250_unregister_port().

Fixes: d962de6ae51f ("serial: core: Fix serial core port id to not use port->line")
Signed-off-by: Tony Lindgren <tony@atomide.com>
---
 drivers/tty/serial/8250/8250_core.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c
--- a/drivers/tty/serial/8250/8250_core.c
+++ b/drivers/tty/serial/8250/8250_core.c
@@ -1204,6 +1204,7 @@ void serial8250_unregister_port(int line)
 		uart->port.flags &= ~UPF_BOOT_AUTOCONF;
 		uart->port.type = PORT_UNKNOWN;
 		uart->port.dev = &serial8250_isa_devs->dev;
+		uart->port.port_id = line;
 		uart->capabilities = 0;
 		serial8250_init_port(uart);
 		serial8250_apply_quirks(uart);
-- 
2.41.0