On Wed, Jul 15, 2026 at 11:37:05AM -0400, Hugo Villeneuve wrote:
> From: Hugo Villeneuve <hvilleneuve@dimonoff.com>
> 
> With CONFIG_SERIAL_8250_HUB6=m, we have the following compile error:
> 
>   ../drivers/tty/serial/8250/8250_hub6.c:46:6: error: redefinition of
>        'hub6_match_port'
> 
> Fix hub6_match_port() prototype definition by using IS_REACHABLE() to
> support both built-in and module values, and substitute empty prototype
> otherwise.
> 
> Fixes: 3d406299d8829 ("serial: 8250_hub6: add hub6_match_port()")
> Reported-by: kernel test robot <lkp@intel.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202607150717.2YxVdWpX-lkp@intel.com/
> Signed-off-by: Hugo Villeneuve <hvilleneuve@dimonoff.com>

I hit the same problem and fixed it similarly[1] before spotting this
patch.

> ---
>  drivers/tty/serial/8250/8250.h | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/tty/serial/8250/8250.h b/drivers/tty/serial/8250/8250.h
> index 9d1068d0489dc..b62f88eec881f 100644
> --- a/drivers/tty/serial/8250/8250.h
> +++ b/drivers/tty/serial/8250/8250.h
> @@ -8,6 +8,7 @@
>   */
>  
>  #include <linux/bits.h>
> +#include <linux/kconfig.h>

This isn't really needed, because the compiler is called with

	-include $(srctree)/include/linux/kconfig.h

which I think you can rely on. But it also doesn't hurt.

>  #include <linux/serial_8250.h>
>  #include <linux/serial_core.h>
>  #include <linux/dmaengine.h>
> @@ -334,7 +335,7 @@ 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_REACHABLE(CONFIG_SERIAL_8250_HUB6)

I picked IS_ENABLED(). Both work fine here. (IS_ENABLED() has the slight
(maybe subjective) advantage to break if CONFIG_SERIAL_8250_HUB6 is
enabled but not reachabe (which currently cannot happen).

Anyhow:

Reviewed-by: Uwe Kleine-König <u.kleine-koenig@baylibre.com>
Tested-by: Uwe Kleine-König <u.kleine-koenig@baylibre.com>

Best regards
Uwe