Re: [PATCH] serial: 8250_hub6: Fix double definition for hub6_match_port()

Hi Uwe,

On Mon, 20 Jul 2026 12:31:31 +0200
Uwe Kleine-König (The Capable Hub) <[email protected]> wrote:

> On Mon, Jul 20, 2026 at 10:08:12AM +0200, Uwe Kleine-König (The Capable Hub) wrote:
> > With CONFIG_SERIAL_8250_HUB6 configured as module
> > (CONFIG_SERIAL_8250_HUB6=m) the cpp symbol CONFIG_SERIAL_8250_HUB6 isn't
> > defined (only CONFIG_SERIAL_8250_HUB6_MODULE is). In this case
> > hub6_match_port() is defined in drivers/tty/serial/8250/8250.h as static
> > inline and in drivers/tty/serial/8250/8250_hub6.c as normal function.
> > 
> > Use IS_ENABLED() to also handle the modular case correctly.
> > 
> > Fixes: 3d406299d882 ("serial: 8250_hub6: add hub6_match_port()")
> > Signed-off-by: Uwe Kleine-König (The Capable Hub) <[email protected]>
> > ---
> >  drivers/tty/serial/8250/8250.h | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/tty/serial/8250/8250.h b/drivers/tty/serial/8250/8250.h
> > index 9d1068d0489d..fb9a7117d145 100644
> > --- a/drivers/tty/serial/8250/8250.h
> > +++ b/drivers/tty/serial/8250/8250.h
> > @@ -334,7 +334,7 @@ int fintek_8250_probe(struct uart_8250_port *uart);
> >  static inline int fintek_8250_probe(struct uart_8250_port *uart) { return 0; }
> >  #endif
> >  
> > -#ifdef CONFIG_SERIAL_8250_HUB6
> > +#if IS_ENABLED(CONFIG_SERIAL_8250_HUB6)
> >  bool hub6_match_port(const struct uart_port *port1, const struct uart_port *port2);
> >  #else
> >  static inline bool hub6_match_port(const struct uart_port *port1, const struct uart_port *port2)
> > 
> > base-commit: 0718283ab28bc3907e10b61a6b4be6fefa1cbb2f
> 
> There is an earlier fix already at
> https://lore.kernel.org/linux-serial/[email protected]/
> 
> It's a bit different, but essentially equivalent. So please stick to
> that older patch.

They are not essentially equivalent. If 
CONFIG_SERIAL_8250=y and CONFIG_SERIAL_8250_HUB6=m, and using
IS_ENABLED() gives this linker error:

ld: vmlinux.o: in function `uart_match_port':
(.text+0x723aac): undefined reference to `hub6_match_port'

Using IS_REACHABLE() fixes this.

-- 
Hugo Villeneuve