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

["Uwe Kleine-König" <u.kleine-koenig@baylibre.com>]

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On Mon, Jul 20, 2026 at 10:07:08AM -0400, Hugo Villeneuve wrote:
> Hi Uwe,
> 
> On Mon, 20 Jul 2026 12:31:31 +0200
> Uwe Kleine-König (The Capable Hub) <u.kleine-koenig@baylibre.com> 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) <u.kleine-koenig@baylibre.com>
> > > ---
> > >  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/20260715153707.4181828-1-hugo@hugovil.com/
> > 
> > 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.

Oh, I read too quickly over the dependencies, I thought
SERIAL_8250_HUB6's

	depends on SERIAL_8250 != n && ISA && SERIAL_8250_MANY_PORTS

would prevent that. With this configuration and IS_REACHABLE I wonder if
it's an issue that hub6_match_port() returns false in
drivers/tty/serial/serial_core.c.

Best regards
Uwe

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