Why flush cache in insw/outsw ?

[<tak...@op...>]

Currently, shmin can't compiled because of flush_dcache_all() in io_generic.c.
SH3 doesn't have flush_"d"cache_all().
Could you please tell me why the flush operations has come here?
Adding dummy flush_dcache_all() in cache_flush.h is easy, though.
/yoshii

cg-diff -pr 9c57548f17806ffd8e4dc4f7973ce78bbfbc2079 arch/sh/kernel/io_generic.c
...
> @@ -96,6 +96,7 @@ void generic_insw(unsigned long port, vo
>         while (count--)
>                 *buf++ = *port_addr;
>  
> +       flush_dcache_all();
>         dummy_read();
>  }
>  
> @@ -170,6 +171,7 @@ void generic_outsw(unsigned long port, c
>         while (count--)
>                 *port_addr = *buf++;
>  
> +       flush_dcache_all();
>         dummy_read();
>  }